The Top 10 of Physics

The Top 10 Uses of Physics During the Summer

1)             Let’s say it’s a regular summer day and you are planning to go to the beach (and you live near the beach).  So, you wake up and make a smoothie for breakfast. This smoothie would not be a possibility without physics! There is a motor in the blender, which allows the blender to work. How does this motor work?

Electrical energy is converted to mechanical energy. A current carrying wire feels a fore in a magnetic field. That is the underlying principle. Then, the force the loop feels will cause a torque. This torque will cause a spin and will cause the blender to rotate.

           

2)             While drinking your smoothie, you turn on the television.  Even this simple gesture involves physics. All houses are wired in a parallel circuit. A parallel circuit has electrical devices connected to the same two points. The pathway for current from one end of the battery to the other is completed if only one device is running rather than all the devices in the circuit.  The more appliances added to the circuit the resistance decreases, the current increases, the brightness remains constant and when one device isn’t working or being the used the rest are not affected. Households use parallel circuits because it is more efficient. Parallel circuits allow households to run multiple devices without running other devices unlike series where it is all or nothing. This is why you can turn the television on without turning on the rest of the devices in the house. The only major disadvantage to parallel circuits is the heat factor. The more current and less resistance there is (which happens the more devices are on), there is high heat, which could potentially turn into a fire. A fuse/circuit breaker prevents this from happening. A fuse is used to prevent the current from getting to this dangerous level. The fuse melts and snaps turning the circuit off. A fuse is used in parallel circuits but it is set up in series.

3)             If you are planning on going to the beach, it would be wise to check the tides before you went. Tides are caused by the difference in force felt by the opposite sides of the earth. Whichever side is closer to the moon will feel the greater force. There are two high tides and two low tides each day (4 tides per day total). High to low tide has a time span of 6 hours and from high tide to high tide and low tide to low tide there is a time span of twelve hours. There is not a specific time each day at which these tides occur. It’s constantly changing because the moon is constantly orbiting the earth. It takes about 27 days for the moon to complete a full orbit. There is a tidal bulge that forms around the earth.

There are two tides we learned about called neap tides and spring tides. During spring tides the moon is either a full moon or a new moon and the tides are at its highest highs and lowest lows. Hurricane Sandy was so destructive because it came at a full moon therefore it was a spring tide so the tides were at its most extreme. If Hurricane Sandy had come during a neap tide or a half moon, the damage would have been much less severe. This is because during neap tides, the high tides aren’t as high as usual and they aren’t as low as usual. Here are images of each to show the position of the earth, moon, and sun during each of these tides.

To the left is an image of spring tides. There are two moons in this picture two show that the moon can either be to the left or right of the earth during spring tides. Also notice the tidal bulge is directed towards wherever the moon is.  The high tides will be where you see the tidal bulge and the low tides will be above and below the earth.

To the right is an image of neap tides. Again there are TWO moons in this picture to show that the moon can either be directly above or below the earth during neap tides. Also notice the tidal bulge is directed towards wherever the moon is.  The high tides will be where you see the tidal bulge and the low tides will be to the left and right of the earth. (High tides and low tides occur on opposite sides of the earth.)

An important note to keep in mind when thinking about tides is that lakes don’t experience tides. Lakes don’t experience tides like the ocean does because the mass of the lake is not nearly big enough to be affected by the pull of the moon.  

So, before going to the beach, it is key to know whether it will be high tide or low tide because it is constantly changing.

4)              You decide to pack a lunch for the beach. So, you cut up watermelon to put in a ceramic bowl and put plastic wrap to cover the watermelon. This plastic wrap doesn’t just magically stick to the bowl.  Thanks to physics we know why exactly, the plastic wrap sticks to the bowl. The plastic wrap is charged by friction and when brought near the bowl, the bowl polarizes. The positive charges in the bowl move close to the negative plastic wrap and the negative charges in the bowl move away from the plastic wrap. The distance between the opposite attractive chargers is smaller than the distance between the like repelling charges. Coulomb’s law states that the force between any two charges are inversely proportional to the distance. F=kq1q2/d^2. Because there is a greater distance between the repulsive forces, the forces between them will be less than closer attractive forces. Therefore, the plastic sticks to the ceramic bowl. [INSERT IMAGE]

5)              Finally you’re on the road to the beach. You are talking to your friend and realize there is a stop sign. You stop suddenly because you weren’t paying close enough attention. Luckily, all cars have headrests and seatbelts. When the car is moving, everything else in the car is also moving. If the car comes to an abrupt stop, everything keeps moving that is not attached to the car. We know this because according to Newton’s First Law, when an object is in motion it will want to stay in motion unless a force is acted upon it. Therefore, your head and your body will want to keep moving forward. The seatbelt prevents your body from continuing forward through the car. Your head pulls backward naturally and would continue moving backwards, however the headrest acts as a force to prevent your head from continuing backwards. Thanks to car designers knowledge on physics and Newton’s First Law of Motion, you’re safe and are able to continue on to the beach.

6)              You continue on your way and approach a stoplight. How does this stoplight work? Well, physics makes this answer simple. In the pavement, there is a loop of wire. When the car, which is magnetic, moves over the wire, it changes the magnetic field of the loop. This change induces voltage, which causes a current. [Mechanical energy is converted to electrical energy.]This current is a signal to the stoplight to change allowing you to continue on to the beach.

7)              Finally you get to the beach, you carry the lunch cooler to the beach. Although this may feel challenging and it may feel like you are doing a lot of work, however, in physics terms, you are actually doing NO work. The force, which is the cooler, being pulled down by gravity is not parallel to the horizontal distance the cooler is moving. Work is the effort exerted on something that will change its energy. Work equals force times distance. [Work=Force X Distance] Work is measured in Joules. The force and distance must be parallel to one another in order for there to be work done.

8)              You and your friends decide to race on the beach. The fundamentals of running comes from physics too. All runners bend their legs when they run because they are moving their legs closer to their axis of rotation (their hips). We know this is important from the property of rotational inertia. Rotational inertia is the property of an object to resist changes in spin or rotation. It is not based upon the mass of an object, rather where that mass is located or how it is distributed (how far it is from the axis of rotation). Therefore, runners bring their mass closer to the axis of rotation to lower their rotational inertia. The farther away from the axis of rotation, the higher rotational inertia an object has.

9)              After a long day at the beach, the typical summer afternoon storms rolls in. What causes lightning? Lightning is a good example of induction. Charging by induction takes place during thunderstorms. The clouds are negatively charged by friction and the clouds positively induce the ground.  The attractive forces eventually become strong enough to produce lightning. Therefore lightning starts from the ground, travels upward and then recedes toward the ground. (Click on image for a closer view.)

10)           On your way back into town, you decide to drive through downtown (Beaufort), the storm hasn’t reached downtown yet and people are walking on the streets and horses are pulling buggies filled with tourists. How can a horse possibly do this? The reason the horse pulls a buggy is because of a few things. We know the horse exerts the same force on the buggy that the buggy exerts on the horse because of Newton’s Third Law which states that every action has an equal and opposite reaction. But the reason the horse and the buggy move forward is because the horse pushes on the ground with a greater force than the buggy pushes on the ground. A key part of this drawing is that the pink arrows are larger than the grey arrows to show that the horse has a greater force than the buggy. So here are the action reaction pairs; the grey would be buggy pushes on earth forward and earth pushes on buggy backward. The orange would be, the horse pulls buggy forward and the buggy pulls the horse backward. Lastly, the pink would be the horse pushes on the earth forward and the earth pushes on the horse backward. Therefore, the horse is able to pull the buggy forward. 

Unit 7 Blog Post

Unit 7 Blog Post

            This was our LAST unit. This unit we learned all about magnetism; magnetic poles, electromagnetism, forces on charged particles in the electric field, motors, generators, energy production, transformers and energy transfer from a power company to a household.

            We began the unit by learning the basics of magnets. Moving charges are the source of all magnetism. All magnets have a north and south pole. The Earth has geographic poles (north and south) as well as a magnetic field with north and south poles. Domains are clusters of elections spinning in random directions. Domains that are aligned have a north and South Pole where as unaligned domains do not have north and south poles. If you cut a magnet in half it will have north and south poles on each half. The field lines inside of a magnet run north to south and the field lines outside of a magnet run south to north. Like poles of magnets repel and opposite poles attract. Like poles repel because the field lines are running in opposite directions where as opposites attracts because the field lines are running in the same direction.

            An example that explains many of these magnetism concepts, it explains why a paperclip sticks to a magnet. A paper clip is not always magnetized. Domains in a paper clip are random [domain is a cluster of electrons that are spinning in the same direction]. All magnets have a magnetic field. When the magnet is close to the paper clip, the domains of the paper clip align to match the magnetic field of the magnet. The paper clip now has a north pole and a south pole and the north pole of the paperclip is attracted to the south pole of the magnet and thus the paper clip sticks to the magnet.

            When learning about magnetic poles we also learned about how a compass works and we learned about cosmic rays, which cause the northern lights. Northern lights are caused by cosmic rays. Cosmic rays that try to enter at the equator are deflected because they are perpendicular to the Earth’s magnetic field whereas at the poles, cosmic rays are parallel to the magnetic field, therefore they can enter the Earth. Cosmic rays are extremely dangerous to humans however because they shoot through human DNA causing serious health issues.

            Next we learned about electromagnetism. A current carrying coil of wire is an electromagnet. The number of turns in the coil increases the voltage of the wire which increases the current therefore strengthening the magnet.

            Following electromagnets, we learned about electromagnetic induction, which is the phenomenon of inducing voltage by changing the magnetic field in loops wire. The changing motion between a wire and a magnetic field induces voltage. The more loops moving in the magnetic field, the more voltage there will be making it more difficult to push the magnet into a coil (a greater resistance). It is a loop of wire in a complete circuit, a magnet is inserted through or around the loop of wire and that changes the magnetic field of the loops.  The induced voltage makes a current. This change in magnetic field induces a current. The amount of current produced by electromagnetic induction depends on induced voltage, the resistance of the coil and the circuit, and changing a current in a nearby loop. The current will be a signal. If we continuously change the magnetic field, that is how a generator works. Electromagnetic induction and generators turn mechanical energy into electrical energy and motors turn electrical energy into mechanical energy. [Mechanical energy is a magnet physically moving whereas electrical energy is current in the wire.] Electromagnetic induction is a part of our daily lives. It can be found in various devices such as metal detectors, traffic lights, credit cards, etc.

            In the pavement, there is a loop of wire. When the car, which is magnetic, moves over the wire, it changes the magnetic field of the loop. This change in the magnetic field induces voltage, which causes a current. This current is a signal to the stoplight to change. Metal detectors and credit card machines undergo a similar process.

Next, we also learned about how a motor works. This explanation can be found in my previous blog post.

We learned about both motors and generators. Motors and generators have almost identical construction but opposite roles. Motors turn electrical energy into mechanical energy, whereas generators turn mechanical energy into electrical energy. A key note to remember about motors is that moving charged particles feel a force when moving perpendicular to a magnetic field. The force felt by the wire causes a torque. Motors work from the force of the magnetic field. Motors can be used for cars, fans, blenders, etc. Generators use resources such as wind, water, steam, etc and turn loops of wire inside of a magnet. It relies on the change in the magnetic field rather than the force of the magnetic field. This change in the magnetic field induces voltage which causes current, which is the current we tend to use in our households.

We concluded our unit with transformers. Have you ever wondered about the little box in your computer charger? This little box is actually a transformer and is used to connect your computer to a wall socket allowing it to charge. We learned that transformer is a device used for increasing or decreasing voltage or transferring electric power from one coil of wire to another through electromagnetic induction. A transformer is simply two coils of wire. There is a primary coil and a secondary coil. The primary coil is connected to the power source so it is the input and the secondary coil is the output. Whenever the primary switch is opened or closed, voltage is induced in the secondary current. AC current is running through the primary, which causes change in the magnetic field. This changes the magnetic field of the secondary at the same rate. DC current cannot be used for a transformer because the current it produces only moves in one direction whereas the AC current continuously changes the direction of the current, which causes the change in the magnetic field. The number of turns in the wire is directly proportional to the voltage induced. The more turns in the wire, the more voltage there will be. The less turns the less voltage there will be. If the secondary has more turns the primary it will produce more voltage than the primary and the voltage will said to be stepped up. If the secondary has less turns than the primary it will produce less voltage than the primary and the voltage will said to be stepped down.

This formula shows the relationship between the primary and secondary:

[# of Primary Turns/Primary Voltage = /# of Secondary Turns/Secondary Voltage]

-The power in the primary is equal to the power in secondary.

[Power Primary=Power Secondary]

Note that [Power=CurrentXVoltage]

So [IV=IV] and the proportions change based on the levels of current and voltage

[Iv=IV]

*An Important Note: keep in mind is that the energy always remains constant due to the conservation of energy, it never changes.

This unit I particularly struggled with transformers. I was confused between the primary and the secondary and which one was the input and which one was the output. I overcame this by re reading my notes as well as further explanations in the book. Although we had to read those pages for homework, I was confused when I read them the first time. However, the second time I read about transformers, I was writing my podcast script so I was paying close attention to detail and was able to record all of it. I also realized it helped me to draw a picture of a transformer rather than to remember different variables in my head when solving a problem.

Although some of the quizzes I did not do as well on as I would have liked, I felt like this unit I clarified most concepts as I learned them. In other words, I understood concepts more easily in this unit than I have in previous units in part due to my persistence in fully learning each concept along the way. I think a part of this unit that really helped with my problem solving skills was the motor project. I had to understand how motors worked in detail, in order for my own motor to work. It was really cool to put my physics knowledge into action. Although I struggled with quizzes this unit, the quizzes helped me a lot. Most answers that I missed I got partial credit because I answered part of the question but not the other parts fully. I corrected these quizzes whenever I got them back and it helped me pay closer attention to the details that I was overlooking.

Podcast Video will be posted Wednesday, May 1. 

Motor Blog

Motor Blog:

There are a few key parts to the creation of the motor made in class; a battery, a coil of wire, a paperclip, and a magnet. The battery provides the current allowing the motor to function. It uses electrical energy to become mechanical energy. The coil of the wire or the motor loop carries the current. The coil of the wire feels the force causing torque. [A current carrying wire feels a force in a magnetic field and force can cause torque]. The paperclip completes the circuit; it carries the current to the wire (which is a part of the motor loop).  The magnet provides the magnetic field.

A motor is a current carrying wire that feels a force in a magnetic field. The more wire and the stronger the magnet, the stronger the force. This force comes from the motor loop deflecting the magnetic field. The coil of the wire has been shaved on one side on both ends so that the current in the coil of the wire flips the direction with each half turn in a continuous direction creating a motor.

You could potentially put small wheels on either side of the motor loop and the simple motor I made could be used as a miniature car. It could be a new type of mouse car project, where you create a miniature car to show your understanding of multiple physics concepts such as torque and magnetism. The motor would function identically to the paragraph described above. I would use more wire and a stronger magnet however, so that the car could experience a greater force therefore move at a faster speed.

To the right is a picture of a simple electric motor similar to the one I made in class. It has the labeled parts as well as the direction of the current.

Magnetism Source

http://www.youtube.com/watch?v=ak8Bh9Zka50

            This source was particularly useful in explaining the basics of magnets. I liked how it explained that the Earth has a magnetic field and that all magnets have a north and south pole no matter what. One interesting part of the video was when the boy was pretending to take away the paper clips with magic when really he was using a magnet to pull the paper clips away. A paper clip is not always magnetized. Domains in a paper clip are random [domain is a cluster of electrons that are spinning in the same direction]. All magnets have a magnetic field. When the magnet is close to the paper clip, the domains of the paper clip align to match the magnetic field of the magnet. The paper clip now has a north pole and a south pole and the north pole of the paperclip is attracted to the south pole of the magnet and thus the paper clip sticks to the magnet.

Unit 6 Blog Reflection

Physics Unit 6 Blog Reflection

            This unit we learned about major physics concepts involving electricity and more specifically; charges, charge transfer, polarization, electric fields, Coulomb’s Law, electric potential difference (voltage), current, types of current, source of electrons, Ohm’s Law, power, parallel circuits, and series circuits.

             Electricity a term used to represent a wide range of electrical phenomena that underlies everything around us. In order to understand a small portion of this huge part of life, we dissected it into different concepts. We began with electric charges. A charge can either be positive or negative. Protons have a positive charge and electrons have a negative charge, neutrons do not have a charge. Like charges repel; opposite charges attract. The transfer of electrons from one place to another causes charge. There are three ways for this transfer to happen; direct contact, friction or induction.  Direct contact and friction are self-explanatory for the most part. However, induction is a little bit more complex.  Induction happens when you bring a charged object near a conducting surface.

            Lightning is a good example of induction. Charging by induction takes place during thunderstorms. The clouds are negatively charged by friction and the clouds positively induce the ground.  The attractive forces eventually become strong enough to produce lightning. Therefore lightning starts from the ground, travels upward and then recedes toward the ground. This example also includes the idea of conductors versus insulators. Lightning rods are conductors. The main purpose of a lightning rod is to prevent a fire caused by lightning. Lightning rods are sharp, tall, and filled with positive charges. It will direct the lightning to the rod and to the ground rather than to the structure. The lightning is conducted into the ground rather than the house. Conductors allow the flow of electrical charge and insulators prevent the electrical charge. 

            Then, we learned about polarization. Induction can be found with conductors as well as insulators. Polarization is the separation of charges. A polarized object is still neutral because the charges are only separating; the electrons are not increasing or decreasing. An example we learned about that explains this as well as Coulomb’s Law is the reasoning behind why plastic wrap sticks to a ceramic bowl. The plastic wrap is charged by friction and when brought near the bowl, the bowl polarizes. The positive charges in the bowl move close to the negative plastic wrap and the negative charges in the bowl move away from the plastic wrap. The distance between the opposite attractive chargers is smaller than the distance between the like repelling charges. Coulomb’s law states that the force between any two charges are inversely proportional to the distance. F=kq1q2/d^2 Because there is a greater distance between the repulsive forces, the forces between them will be less than closer attractive forces. Therefore, the plastic sticks to the ceramic bowl. 

            Electric field is the area around the charge that can influence another charge. We draw electric fields in which direction a positive charge would pull. The closer the lines are together the stronger the electric field. The farther away you are from an electric field, the weaker it is. It is important to remember the difference between electric fields and gravitational fields is that various materials can shield electric fields, whereas gravitational fields cannot be shielded. Metal can completely shield an electric field. The electric field inside the metal encasing will feel no force by any charges outside of the shield. The filed inside will field no force no matter what. This is often why electronics are encased in a metal shield, so that the device inside of the metal case will feel no force outside of it, therefore it can function. 

            Next, we learned about the importance to know the difference between electric potential and electric potential energy. A charged object has potential energy through its location in an electric field. Electric potential energy is the energy a charge has due to its location in an electric field whereas electric potential, otherwise known as voltage and measured in volts, is equal to electric potential energy (in joules) over the charge (in coulombs). V=PE/Q.

            Following this we learned about electric energy storage. A capacitor is a common device where electric energy can be stored.

            The difference in potential energy is when the ends of an electrical conductor are at different electric potentials, charge flows(charge flowsàwhich is current) from one end to the other. The flow of the charge continues, as along as there is potential difference. When there is no potential difference, no charge flows. Charge flows when there is a high voltage and a low voltage and will stop when they are both an equal voltage. The rate of electrical flow, current, is measured in amps. Current will only work if there is a difference in electric potential. A key note to remember is that voltage causes current. Current does not cause voltage.

Take batteries for example. Batteries are able to have current because they have a difference in electric potential or a difference in voltage. Overtime, the difference decreases and eventually there is no longer an electric potential difference. When there is not an electric potential difference, there is no current, which is why batteries stop working.

Another example explains why flashlights get dimmer as the battery becomes weaker. A flashlight gets dimmer as the battery becomes weaker because the difference in voltage decreases, voltage causes current and the less current there is to light the bulb, the dimmer it will be.

Also, the idea that to complete a circuit, there must be current. This current comes from the potential difference from the high voltage to the low voltage. This is why birds aren’t harmed when sitting on a power line wire. If birds are standing on only one wire, they are not completing the circuit because they aren’t touching the ground (which would conduct electricity through their bodies and into the ground) and they aren’t touching the two wires at the same time. This means there’s no current meaning that there is no electric potential difference.

The amount of current that exists depends on the voltage as well as the electrical resistance, the conductor, which offers the flow of charge. The resistance of a wire depends on the thickness, length, and material. The thicker, the shorter, and the better conductor material, and the colder the wire is, the wire is the less resistance there will be meaning there will be more current. Electrical resistance is measured in ohms. 

Ohm’s law states that current in a circuit is directly proportional to the voltage and is inversely proportional to the resistance of the circuit. Current(amps)=voltage(Volts)/resistance(ohms)

Electric shock can be damaging from the current passing through the body. This current that runs through your body depends on both the voltage used and the electrical resistance of the body. To receive a shock, requires a difference in electric potential from one part of your body to another part. As long as you are wearing some sort of insulator or you are standing on an insulator, or you are not completing the circuit, you will not feel any shock not allowing the current to run through your body.

Another key factor to keep in mind is that “high voltage” does not necessarily mean high danger; the danger factor rests upon the amount of stored energy there is.

Look at this plug, the round prong connects the rest of the appliance directly to the ground. Any charge built up on the appliance is then conducted to the ground, which prevents accidental shock. We briefly discussed direct current and alternating current. Electric current can come in two forms; dc or ac. DC is direct current, which refers to the flowing of charges in ONE direction. A battery uses direct current. AC is alternating current, which moves in one direction and then the opposite direction and moves in this path continuously. Households use AC current.

            Think about flipping on a switch to a light in a room. The lights work immediately when the circuit is completed. Current is established through the wires at nearly the speed of light. It is not the electrons that are moving quickly, in fact the electrons are moving very slowly but the electric signal moves nearly at the speed of light. Another misconception about electrons is the idea that electrons flow from the outlet into a lamp but it is actually, when you plug a lamp into an outlet, energy flows from the outlet into the lamp.

            Moving onto electric power, electric power is equal to current times voltage. P=IV and the relationship between energy and power is simply. Power=Energy/Time

            The last concept we covered was electric circuits. A circuit is any path along which electrons can flow. There are two types of circuits; series and parallel. A series circuit has all devices connected end-to-end, which forms one path for electrons to flow. The more appliances added the more resistance increases, current decreases, brightness (power output) decreases, and when one light bulb stops working or is removed, they all stop working. A parallel circuit has electrical devices connected to the same two points. The pathway for current from one end of the battery to other is completed if only one light bulb is lit rather than all light bulbs in the circuit.  The more appliances or light bulbs added to the circuit the resistance decreases, the current increases, the brightness remains constant and when one light bulb stops working, the rest are not affected. Households use parallel circuits because it is more efficient. Parallel circuits allow households to run multiple devices without running other devices unlike series where it is all or nothing. The only major disadvantage to parallel circuits is the heat factor. The more current and less resistance there is (which happens the more devices are on), there is high heat, which could potentially turn into a fire. A fuse/circuit breaker prevents this from happening. A fuse is used to prevent the current from getting to this dangerous level. The fuse melts and snaps turning the circuit off. A fuse is used in parallel circuits but it is set up in series. 

            This unit has been particularly challenging for me. I struggled with understanding each and every concept we learned to its fullest because there were so many concepts to go over. I became frustrated with learning the process of lightning, capacitors, and the difference between electric potential and electric potential energy. The confusion with these concepts lead me to not do as well on quizzes that I would have liked. 

             However, I overcame these struggles by taking each concept step by step. I went through the book and looked the examples used and compared them to my notes. I was able to use more detail with the examples and have a better understanding of each one. Also, I went through each quiz and corrected what I got wrong so that I could understand it more clearly and not mess up on the test. 

             My problem solving skills this unit were slow but comprehensive. I tried my best to understand the material I was unclear about. I went in for help various mornings, usually before quizzes. I always completed my homework in detail and corrected my answers in class if I got questions wrong. I think labs were particularly useful for me as well as group work because our groups could bounce information and answers off one another without a group shutting down the other group. 

            

Unit 6 Photo

            Have you ever taken a balloon, rubbed it on your head and put it on the wall and it stuck to the wall? Well, this unit, I learned the physics behind this. Notice in the picture the balloons are sticking to the wall. The balloons were charged with friction when they were rubbed on people’s hair and were given a negative charge. When one of these balloons is brought near the wall, the wall polarizes, meaning the positive charges in the wall move close to the negatively charged balloon and the negative charges in the wall move away from the balloon. The attractive charges will be closer together and the repulsive charges will be farther apart. Coulomb’s Law, F=kq1q2/d^2, states that force is inversely proportional to the distance and directly proportional to charges. Therefore, the attractive charges have a greater  force because their distance is smaller which is why the balloon sticks to the wall.

Although the picture above demonstrates a real life situation when the balloon sticks to the wall, here is an animated version that can show the explanation of polarization and the difference forces.  

Mousetrap Car Blog Reflection

Newton’s first law of motion states, “Every object continues in a state of rest or uniform speed in a straight line unless acted on by a nonzero net force.” In other words, an object will stay at rest until a force is acted upon it and an object will stay in motion unless a force is acted upon it.”  Theoretically, the construction of our mousetrap car seemed pretty simple because the force of the mousetrap would cause our car to move forward and according Newton’s first law to continue moving forward. However, we had to keep in mind the FORCES that would act on our car to prevent it from continuing in motion such as friction. We had to create a force that was larger than the other forces acting on the car.

Newton’s second law of motion states that force causes acceleration therefore force is directly proportional to acceleration and acceleration is inversely proportional to mass. (a=fnet/m). This law was key in our construction of the car. If the force was larger then the acceleration would be larger too. The more acceleration the car has the better chance of the car going the distance of 5 meters and going faster than other cars in the project. Also, we needed to keep a lighter frame and lighter axels for the car so its mass would be less and it would have a greater acceleration.

Newton’s Third Law states that every action has an equal and opposite reaction. Newton’s second law can be explained in the formula  (a=Fnet/m)which explains that acceleration is directly proportional to force and indirectly proportional to mass. Newton’s Third Law can use this same formula but you can write it in a different way: (F=ma). The fact that every action has an equal and opposite reaction was important for our car because we needed keep in mind that no matter what the ground would pull down on the car and the car would pull up the ground with an equal and opposite force, so the car needed to be strong.  For example if this was our mouse trap car; Car F (10N) =mA the force would be the same either way, but to control the distance and speed the car went we would need to increase the acceleration rather than its mass.

The two frictions present in this project were static and kinetic friction. Friction played a big role in a project with its advantages as well as its disadvantages. When constructing the car, we had to take into account the level of friction we wanted the car to have on its wheels. At first, I thought it would make more sense to have the least amount of friction on the wheels as possible because according to Newton’s first law an object will stay in motion until a force is acted upon it. (I thought friction would only be a disadvantage.) So, I thought if there was no friction on the wheels there would be no force acting on our car and it would keep moving. However, I soon realized that friction on the wheels would be vital for our car to move. We put friction on the back wheels so the car would be able to have traction to move across the floor. Otherwise the wheels would just have been spinning without going anywhere. However, we did not put any type of friction on the front wheels to allow the wheels to spin freely and quickly. In this way friction was used to our advantage. Finding the materials to use to create enough friction on the back wheels but not too much was also a challenge. But after doing some research, wrapping cut up balloons around the back wheels seemed to be the best solution.

We chose to do four wheels for our mousetrap car because we thought four wheels would give our car the best stability. At first, we planned to make the back wheels larger than the front wheels, however, in the end we decided to use four discs. The back wheels were CDs and the front wheels were DVDs. This was because the DVDs were significantly lighter than CDs, so we wanted to have less mass on the front axel so the wheels could move more quickly with a lighter mass whereas the back wheels (attached to the back axel) needed to be heavier for the level of friction and mass. Extremely large wheels seemed like a good idea because they could cover a greater distance in a shorter amount of time and the small wheels seemed like a good idea because they could move faster in a shorter amount of time. This is why we originally had our car designed this way. However, we found a moderate balance with the CDs and DVDs and decided to focus more on the mass rather than the size. We wanted to keep the design simple and the equal sized wheels made it easier to do so.

The conservation of energy states that energy cannot be created or destroyed; it may be transformed from one form into another; but the total amount of energy never changes. When you think of a system, like a swinging pendulum, there is one thing that is neither created nor destroyed, and that would be energy. The energy may change form, for example, it may turn into heat, however, that does not mean the energy is lost. Take a water dam for instance. The water behind a dam has energy that may be used to power a generating plant below, where it will be transformed to electric energy. The energy will then travel through wires to homes where it can be used for everyday uses. Because we know energy does not disappear or appear, it transforms, we can assume that kinetic and potential energy can transform into one another. This is similar to our mousetrap car. After considering this concept, we knew that the energy in the mousetrap car would be the energy we would be working with no matter what. We could not increase the energy or decrease the energy of the system. However, we could use it more efficiently by storing enough potential energy in the car for the car to transform into the kinetic energy allowing it to go the full 5m. The whole system would have the same amount of energy in the beginning and in the end.

The length of our level arm was a HUGE obstacle in the construction of our car. At first, we started out with no level arm besides string, which we made twice the length of our car. However, our car didn’t move. So a student at UNCA explained to us that the longer the lever arm, the farther our car would go. So, we used a plastic stick (part of a hanger) and attached it to our car. The first run with this lever arm our car went 5m! After trying it again though, the car struggled to go half the distance. It was frustrating and we thought maybe if we made the lever arm longer it would help, but this just made the car topple over and it even did a complete flip in one test run. Then we tried to balance our lever arm so it was more centered. But again the lever arm was just not working for us so we took it off and just used the string; this time the string was much shorter. We also made our axels thinner. If we had constructed the lever arm in a different way, the car may have gone 5m, however, it just did not work for us. So our pulling force was simply the string coming forward with the mousetrap device and pulling the back axel forward causing the back wheels to spin forward.

Rotational velocity is the number of complete rotations per time unit. We wanted our front wheels to have a high rotational velocity meaning it would have more rotations per time unit whereas the back wheels could have a greater tangential velocity. Tangential velocity can also be called linear speed because it is something moving along a circular path. The direction of motion is tangent to the circumference. Tangential speed depends on the distance from the axis of rotation. Inertia is the property of an object to resist change in motion dependant upon the mass. This was important in the construction of our wheels because the larger the wheels the greater distance these wheels would cover in a shorter amount of time even though they would have a smaller rotational velocity.  Rotational inertia is the property of an object to resist changes in the spin of an object. It is dependant upon, not the mass of each object, but where the mass is located on that object, how it is distributed.  It involves the distribution of mass and how far away it is from the axis of rotation. If an object has a small amount of rotational inertia, it is easier to spin compared to an object with a large amount of rotational inertia, which is very difficult to spin. We set up the wheels pretty close together because the less distance the faster the wheels would go.  We also had to make sure we didn’t have the a lot of weight spread out on the car, this is why we used the frame of the car to simply be the mousetrap because it would create a smaller mass that was together creating less rotational inertia on the car. The less rotational inertia our car had the better.

Work is the effort exerted on something that will change its energy. Work equals force times distance. [Work=Force X Distance] Work is measured in Joules. The force and distance must be parallel to one another in order for there to be work done. We cannot calculate the work being done on the spring because the spring is not parallel to the distance the car travels. Potential energy is energy that is stored and held in a stored state that has POTENTIAL of doing work. Potential energy is equal to the combination (multiplied) of mass, gravity, and height.[Potential Energy= Mass X Gravity X Height] We cannot calculate the amount of potential energy being done on the spring because we don’t know it’s mass or its height. Also, we can’t measure don’t know the total energy of the system so it’s not possible to calculate the potential energy. Kinetic energy is the energy of motion. Potential energy can change into kinetic energy. The change in kinetic energy of a moving object depends on the mass of the object as well as its speed. [Change in Kinetic Energy=1/2mass X velocity^2] Anything in motion has kinetic energy. According to the work energy theorem, work equals change in kinetic energy. The change in kinetic energy can’t be measure on the spring because we don’t have enough evidence of the velocity of the spring itself. Acceleration is equal to speed times distance, although we can measure the acceleration of the car, we cannot measure the acceleration of the spring because we don’t know the distance it traveled nor do we know the speed it traveled.  

Our final design was much different compared to our original design. Our original design is in the picture in the blog post before this one. Our final design had a much more simple layout. We learned the smaller the axels and the smaller the mass of the system in general the more functional our car turned out to be. Stability and simplicity were the main goals we had to achieve in order for our car to work, which is why we made a frame for the wheels on our final car.

The mousetrap car was definitely a major struggle for our group partly because our car worked on Friday and then over the weekend it somehow stopped working and forced us to completely start over with the car. We struggled a lot with the lever arm because according to concepts of physics we learned in the past, the longer lever arm the farther the distance the car would go. However, with our car the longer the lever arm the less our car functioned. So we had to take away the lever arm and use string. Also, we struggled a lot with stability. The wheels of our car seemed very shaky especially the front wheels. They kept sliding around causing the car to run into the wall. So, we had to use part of a pen to prevent the front wheels from moving but that took a lot of experimenting and sawing to figure that piece of the puzzle out. Lastly, simplicity is what our design struggled with. We were told that increasing the back axel would help the speed of the car. We used a cork to wrap the string around it but this cork may have been the foundation of our problems. The string let out too quickly so our car couldn’t reach its full energy level. In the end, we had thinner axels (without the cork) and no lever arm and our car went the required distance and it went fast.

If we were to do this project again, I would definitely take the factors of simplicity and stability into account and try to work with those more efficiently. Also, I think the longer lever arm could really help the car go a farther distance, I just think it needs to be constructed differently so the car is more stable. Also, the axel issue seemed like the cork should be extremely helpful with the speed and although it had a negative affect I would like to try and figure out a way to use the thicker back axel and still have the string let out at an equal pace instead of all at once. I think if we re did this project we could really make outstanding cars. 

Mouse Trap Car Design

Unit 5 Blog Post

Unit 5 Blog Post

            This unit we learned about work, power, kinetic energy, potential energy, the conservation of energy, and machines. I thought this unit was particularly cool because throughout the chapter we could see how all the physics concepts related to one another.

            Work is the effort exerted on something that will change its energy. Work equals force times distance. [Work=Force X Distance] Work is measured in Joules. The force and distance must be parallel to one another in order for there to be work done.

            For example, this is a waiter carrying a tray. I automatically assumed that work was being done on the tray. However, there is NO work being done on the tray itself. The force, which is the tray, being pulled down by gravity is not parallel to the horizontal distance the tray is moving.

However, there is work being done on the tray when the waiter lifts the tray. The force of the tray moving upward is parallel to the vertical distance the tray is lifted.

            Here is another example of work. You have the option to take the steeper hill or the more gradual side to get to the field hockey field, yet both sides will take you the same vertical distance. Therefore, the steeper side of the hill and the gradual side would require you to do the same amount of work because work is dependent upon force and the VERTICAL distance you traveled and both hills have the same vertical distance.

            The next concept learned in this unit is power. Power depends on work. Power is equal to the amount of work done per time it takes to do it. Power is measured in watts. The faster work is done, the more power there is.

[Power=Work/Time Interval] Power is measured in Watts. The amount of power is dependent upon how quickly work is done. The faster work is done the more power there will be. But remember the amount work done does not factor any time unit; it is power that depends on work and time.

            In class we had a lab involving walking/running up and down the stairs. The amount of work done when we walked up the stairs versus when we ran up the stairs was the exact same amount because the force and distance did not change. However, the power of walking versus the power of running up the stairs changed because the amount of time it took to go up and down the stairs changed. There was more power when we ran up the stairs because it took less time to complete the work. The faster the work, the more power there is.

            The next concepts we learned about were kinetic and potential energy.  Energy is the ability to do WORK. These two energies come from mechanical energy, which is the energy due to the position of something or the movement of something. Mechanical energy can be in the form of potential, kinetic, or a sum of the two energies. Potential energy is energy that is stored and held in a stored state that has POTENTIAL of doing work. Potential energy is equal to the combination (multiplied) of mass, gravity, and height.

[Potential Energy= Mass X Gravity X Height] A simple example of potential energy is a ball sitting on the top of a cliff about to fall. Another example involves a bow an arrow. When a bow is drawn, energy is stored in the bow. 

            Kinetic energy is the energy of motion. Potential energy can change into kinetic energy. The change in kinetic energy of a moving object depends on the mass of the object as well as its speed.

[Change in Kinetic Energy=1/2mass X velocity^2] Anything in motion has kinetic energy. According to the work energy theorem, work equals change in kinetic energy. Potential energy and kinetic energy are both measured in watts because they are both forms of energy and energy depends on work. Whenever work is done, energy is exchanged. 

            The next concept we learned was the conservation of energy. The conservation of energy states that energy cannot be created or destroyed; it may be transformed from one form into another; but the total amount of energy never changes. When you think of a system, like a swinging pendulum, there is one thing that is neither created nor destroyed, and that would be energy. The energy may change form, for example, it may turn into heat, however, that does not mean the energy is lost. Take a water dam for instance. The water behind a dam has energy that may be used to power a generating plant below, where it will be transformed to electric energy. The energy will then travel through wires to homes where it can be used for everyday uses. Because we know energy does not disappear or appear, it transforms, we can assume that kinetic and potential energy can transform into one another. Here is an example that can help to explain this concept.; Imagine a ball at the top of a cliff about to fall off,  at the top JUST before the ball is falling, it has 10,000J of PE and it has 0 KE. However, as the ball falls, its potential energy decreases and its kinetic energy decreases. However, the total amount of energy remains at a constant 10,000J. Right before the ball hits the ground, its potential energy has decreased to 0J and its kinetic energy has increased to 10,000J. Here we see the transformation of energy.

            When you think of a machine, you might assume it’s a complicated device. However, machines can be very simple. A machine is a device for multiplying force or simply changing the direction of force. Machines reduce or change force but NOT energy and work. The principle of machines comes from the conservation of energy. When you put work in there is an equal amount of work out.

[Work in=Work out] Since work equals force X distance…

[Force in X distance in = force out X distance out] Suppose you are loading a box to a truck. It will take much more force to load the box with a shorter distance than it would be if you were to add a ramp.

Work in (the ramp)= fd

Work out (without the ramp)= fd

Work in=Work out

fd=fd

An ideal machine would work with 100% efficiency. However, all machines have some sort of transformation of thermal energy. If we put in 100 J of work and get out 98 J of work, that machine is 98% efficient. It did not LOSE energy, it just wasted 2% of its energy because that 2% was transformed into heat.

As I mentioned before, this unit ties a lot of its concepts together. This is an example to show this connection of terms:

A 10kg car accelerated from 10m/s to 20m/s in 2 seconds. In that time it traveled 10m.

The change in Kinetic energy the car experience?

Change in KE= 1/2mv^2

Change in KE before= Change in KE after

Change in KE final- Change in KE initial = Change in KE

1/2mv^2 final - 1/2mv^2 initial= Change in KE

½ 10(20)^2- ½ 10(10)^2= Change in KE

½ 10(400)- ½ 10(100)^2= Change in KE

½ 4000 - ½  1000= Change in KE

2000-500= Change in KE

1500J= Change in KE

How much work was done?

Work= Change in KE

Work= 1500J

What was the force that caused the car to accelerate?

Work= fd

1500=F(10)

Force=150N

What was the power during the acceleration?

Power=Work/Time

Power=1500/2

Power=750 Watts

This unit I started out strong with the concepts of work and power, however, I struggled a lot with potential and kinetic energy. I was confused with how they could transform into one another. I especially struggled with the questions asking about the potential, kinetic, and total energy throughout the fall of an object. However, after struggling on an open note quiz, I realized that I needed to clarify whatever was confusing me. So, I looked at the Eureka videos, which helped to clarify my confusions.

            My problem solving skills this unit stayed fairly steady. Once I had clarified my confusions with kinetic and potential energy it was easier for me to make connections between all the concepts. The six problems we did in class were a really useful tool for bringing these concepts together. After going over these problems, my problem solving skills were strong and clear. Although I had a high effort in homework and I always take diligent notes, I did poorly on an open note quiz. This was because although I had the notes and homework, I didn’t have as clear of an understanding as I should have. So, next unit my goal is to catch my confusions like this early on so that I don’t face another poor open note quiz. 

Our podcast had some technical difficulties but our group worked well together, we all collaborated our ideas and my ideas about work were clarified and corrected like on the waiter example. Instead of saying there was no work being done (when the waiter was carrying the tray) I was corrected to say that there was no work being done on the TRAY.