Top Ten

Top Ten Movies in Physics

1.)  Moving Charges Feel a Force in a Magnetic Field:  Brother Bear 

In the movie Brother Bear (2003), The Northern Lights play a significant role in the plot of the movie. While they play a largely symbolic and spiritual role in Brother bear, they can teach us a lot about charges and magnetic fields. 

https://youtu.be/jnJDdaUQNRI?t=52s

If you watch the clip above, you will see an example of thesis northern lights. In the movie, it is not clear why when he touches the blue thing with his spear, the northern lights appear. However, in real life, we can easily understand why we can see them.

The northern lights are cosmic rays that are, because of moving charges, able to enter earth's atmosphere. But, Brother Bear takes place in artic Greenland, presumably among an Inuit tribe there. But when have you ever seen a movie with North American natives that depicts the Northern Lights? The Answer is never, so why are there no Northern lights at these places? Well, to understand why the Northern lights can only be seen at the poles we need to look at the field lines of the earth:

When the charges of the cosmic rays are moving perpendicular to the magnetic field of the earth, as they would need to do to enter the earth at the equator, the charges feel a Force and are forced back into space. However, when the charges try to enter at the poles, they are moving parallel to the magnetic field. You can imagine a charge entering along side the lines at the top. This phenomenon that occurs at the poles is exclusive to the poles because anywhere else, the charges move perpendicular and are forced away. The poles are the white parts at the top, which is where Brother Bear takes place. So whatever the reason be that the Northern Lights appear when they do (with animals prancing on them), it is possible for them to be seen at all because of the way charges feel a force in a magnetic field. 

2.) Falling Through the Air (With Air Resistance and a Parachute). Furious 7 

Skip to 1:01
Parachute is at 2:15

Check out this clip from Fast and Furious 7 (2015) in which cars parachute out of a plane. Aside form this being completely awesome and really entertaining, it can teach us a lot about how things fall through the air.

When the cars first are dropped out of the plane, they are speeding up.

They're acceleration is going up and their Fnet is going down. They velocity is going up. What is happening is that because the car is speeding up (at 1:35 you can see the speed going up), it's Fair is going up and it's Fweight is staying the same. At some speed called terminal velocity in which the Fair and Fwieght are equal.

Here is the Terminal Velocity:

At Terminal Velocity, The acceleration and Fnet are both 0. The velocity is high, but it is constant velocity. (it is hard to see the cars in the picture above, they are the black specs).

Then, the cars/object will open their parachute:

When the cars open their parachute, The velocity goes down but the acceleration up (however, the acceleration is negative because the car is now slowing down). The Fnet goes up. Because the Surface area increases, the Fair increases and so Fnet increases. Because the Fair is greater than Fweight now, the car slows down.

Once the parachute has been opened, it easier for the car to accumulate Fair with all that surface area. So the car reaches another Terminal Velocity which is slower because of the easily acquired Fair.

3.) Impulse:  Magnolia

In the opening scene of Magnolia (1999), a man attempts to jump off a building, however, he does not know there is a net right above the ground and he falls on the net and does not die (he doesn't die from the fall, he does actually get shot accidentally on his way down). Why does would he die from hitting the ground, but doesn't die when he hits the net?




The reason the net prevents window washers or suicidal jumpers from dying is because of Impulse.

Impulse is (J) change in momentum.
The equation for this is:

J=F x change in time
You can think of impulse as the Force applied and the time over which that force is applied.

In this case, Sydney Barringer changes momentum when he hits the net, so what is the difference in his Impulse when he hits the ground and when he hits the net? With both the ground and the net, the momentum is going from the same momentum to 0, so the Impulse, that is, change in momentum, is the same for both. However, the time over which that momentum changes is different. The time of the fall doesn't matter, do not plug that in. What does matter is the time over which the momentum changes which is either when he starts hitting the ground to when he stops or when he starts to hit the net and when he stops. As you can imagine the time for the ground is very very small. The time for the net is also small, but it increases the time of the impulse because when you hit it, it moves and it takes longer to get to 0 momentum. Because the impulse is constant, when the time goes up, the force goes down. So when Barringer hits the net, he doesn't die because the time of the impulse is greater and thus the Force is lower which causes him less injury.

4.) Newton's Third Law: Scott Pilgrim vs. The World

In this scene from Scott Pilgrim vs. The World (2010), Movie Star Lucas Lee skateboards down a whole lot of steps. Skateboarding can tach us a lot about Newton's Third Law.




First of all, Newton's Third Law states that every action has an equal and opposite reaction.
We can look at the skateboard and see that the action of the skateboard is met with an equal and opposite reaction from the ground. You say this like:

Skateboard pushes ground backwards
Ground pushes skateboard forward.

You can show this with a diagram and vectors:

Or you can show the reason he is able to push off and begin moving at the beginning with this action-reaction pair:

The reason that Lucas Lee is able to both push off of the ground to start, and why he is able to keep going forward on the rail is because of friction. When you push off, the wheels do not push harder on the ground, but the wheels have less friction, so they move. The friction is what is important. 

5.) Acceleration:  Any Given Sunday

In this clip from Any Given Sunday (1999), depicted is a play from the final game of the movie. We can sort of see why the linebackers from the team are bigger guys and the running-backs like Jamie Foxx are smaller and lean. 



The explanation of the size of different players comes down to what each players job is. The line backer's job os to stop other players. Their main objective is to prevent other plays from making progress. If we look at the equation for acceleration:

a = F x 1/m 

The linebacker has a lot of mass, and because that is an inverse relationship, it doesn't do any favors for acceleration. However, they harder to move because of this and have an easier time stopping someone in their tracks.

For the running back, their mass is low and they can thus accelerate faster. That is the job of the runner, to run fast. Also this allows for more mobility to doge players because it takes less force to accelerate in different directions.

6.) Charges: Avengers 

In this scene from Avengers (2012), Thor connects with lighting and tries to redirect it. It can show us and help us to explore the role charges play in lightning strikes. 



The reason regular lightning occurs is because the clouds in the sky become charged because of friction and the negative charges are closer to the bottom of the clouds. The ground is positively charged because the clouds have polarized the ground by having the negative charges at the bottom of the clouds attract the positive charges to the surface of the ground. The positive charges start to create a pathway to clouds and when they meet, the negative charges rush to the ground and you can see the path as lightning. then the lightning tries to ground and finds a pointy metal thing that it can go through to get to the ground. In this case, it may be that Thor has some powers that can make lightning just happen between himself and the sky, he obviously has the power to bring the clouds together and charge them through friction by himself. But it is not hard to imagine that the lightning would be attracted to that pointy metal building that is very tall.

7.) Capacitors: Notting Hill

In this ending scene of Notting Hill (1999), the setting is a press conference. When the scene is over, and Anna answers that she will stay in Britain indefinitely, the press commence taking pictures with their cameras that have flashes on them. All of these camera flashes are facilitated by capacitors which are facilitated by charges. 





The way a capacitor works is you have two plates inside the flash of these cameras and they have oppositely charged charges in each plate. So the plates are attracted to each other, you know, like opposite charges do. So then, the flashes charge by adding charges to each side and increasing the attraction but keeping the plates apart. Then, when you don't continue to keep them apart and have recharged their attraction, they rush together and the energy is released very quickly in the form os the flash on the camera's of the press in that room. You cannot have the flash shine continuously because you have to recharge it and because the release of light is inherently quick.


8.) Work: Goodfellas

In this scene from Goodfellas (1990), A waiter carries a able through the room. The question is: Is the waiter doing work on the table as he walks and carries it? Of course! He carries it forward how would it move if he doesn't do work when he carries it? Actually, the waiter in this situation is not doing work on the table. Let's find out why.





Let's start by defining what the heck Work is:

Work = Force x Distance

The important thing to get though is that the Force and Distance of that equation have to be parallel. 
As the waiter carries the table, the Force he exerts is upwards on the table, however, the Distance he carries it is forward. So when the waiter carries that table forward, the Force exerted is not parallel with Distance he carries it so he exerts no work. When he sets the table down, the Distance he brings it down from the air to the ground is parallel to the Force he exerts on it up, and there he does do work on the table. Here is a helpful diagram of what is happening. excuse the goofy caption and lack of resemblance between the red haired waiter and what appears to be a Latino waiter in the movie. 

9.) Rotational Inertia: Catching Fire

In this scene from Catching Fire (2012), The cornucopia in the middle of this area begins to spin and everyone is on it and it is difficult for them hold on. From this scene we can explore some things and explain some things about rotational inertia. 



If Inertia is a thin's resistance to change, rotational inertia is a thing's specific resistance to rotation.
Rotational inertia is lessened if a lot of the objects mass is located near the axis of rotation. In this case, a lot of the mass is near the axis of symmetry. There are some rocks and things on the outside, but the big metal thing is in the middle so that is a lot of mass close to the center.

Therefore, the island in the middle has a relatively low rotational inertia and is less resistant to rotation and gets spinning pretty fast.
Next we might consider the difference between Tangential velocity and Rotational velocity in this case. Consider this moment where Peeta is higher up on the side and has an easier time holding on, but this other girl is closer to the edge and falls off.

Tangential Velocity is your distance covered over time and Rotational velocity is the number of rotations over time. They both have the same Rotational velocity because they are doing the same number of rotations per unit of time. However, because the girl is further out but doing the same rotations, she has to cover more distance and thus has a greater tangential velocity. Perhaps this higher tangential velocity is what made it harder for her to hold on.

10.) Circuits and Wiring: Christmas Vacation

In this scene from Christmas Vacation (1989), Clark has put a lot (a lot, a lot) of string lights on his house so that he can have the brightest house. He is very exited to turn it on only to find that when he plugs it in, not a single bulb turns on. How is it that not even one of the bulbs turns on. Turns out that for string lights it is all or nothing.


Christmas string lights like these are wired in a circuit called a series. This means that the current goes from the battery/source of voltage through all of the bulbs. A bulb in the middle relys on the current to go through the bulbs before it, it doesn't get current straight from the source. It looks like this:

SO the reason that absolutely none of them turns on is because the circuit has been hindered somewhere which means that all of the lights cannot be lit. It turns out that somehow, for movie logic reasons, the lights in the basement of the house are connected the series circuit because when the grandma turns the lights on in the basement, I guess it connects the circuit and completes it so that all the lights turn on. 

This doesn't make buckets of sense, but the lady gets her cake, and it's funny so plot successfully driven forward. Boom. Movie Magic. Physics Magic. 

Wind Turbine Blog

 Wind Turbine Project 

 Overview: Electromagnetic Induction

Making a Wind Turbine work relies on a concept called Electromagnetic Induction. Electromagnetic Induction uses mechanical energy to change the magnetic field of something. This induces a current which causes a current. In the wind turbine, we are using wind to spin magnets over coils of wire which changes the magnetic field. Below you can find our version of making this real.

Materials and Methods:

The materials you will need to build a wind turbine are:

1. Wire (lots of it, you will need to make it into coils)
2. Magnets (at least about four)
3. Electric Tape
4. A Water Bottle
5. A knitting needle 
6. Hot Glue
7. Your own choice of base material (we jus made a structure out of poster board, however, it was sort of shaky. We suggest something more sturdy for any future models). 

Here are some pictures of our turbine:

Here is our Wind Turbine in its entirety:

As an overview: The Windmills/Water bottle is attached to the knitting needle in the middle, as is the plate with magnets on it. When the water-bottle spins, it then spins the magnets. Our structure is made up of a base made out of poster board with wood to reenforce the sides. 

1.)  Here are the coils, which we made four of, each consisting of 200 loops. We taped them to the base of our structure.

We coiled these coils around a strip of cardboard, making sure to be consistent in the direction we wrapped them.  

2.) Here are the magnets, which are located right above the Coils. 

When the needle spins, the magnets spin above the coils which are stationary. The thing we attached the magnets to is a circular cutout from the poster-board. We hot glued magnetic nuts to the poster-board and then the magnets were attracted to the bolts. This way we didn't have to hot glue the Magnets. We used four magnets and four coils. 

3.) Here is a closeup and wide shot of the wings (made out of a helped water bottle). 

In the top photo you can see that we cut the water bottle in half lengthwise and then attached them in an increment in order to create a a surface area that would move from the wind. The water bottle and the magnet plate are both hot glued to the needle. However, you can see that at the top of the base, the needle is not glued. This is so that the bottle and the magnets move freely from the base, which has the coils attached to it. 

Results of Our Wind Turbine:

What we generated: 

We generated .0015 A of current with our wind turbine. 

Lightbulb results: We were not able to light a lightbulb. The concrete explanation is that we did not create enough current to do so. The deeper reason for that is likely that we were not careful enough about our construction. Our base moved a lot when it was spinning and I think that maybe prevented it from being most efficient. 

Here is a video of our Wind Turbine in action. It looks pretty cool, but you can see that it shakes. 

We Generated .002V

Discussion: What Worked and What Didn't.

What Worked:

• Having all your materials when Ms. Lawrence tells you to so you can start right away. Seriously, everyone needs to do this because it is super helpful and mitigates stress. 
• Making sure you keep the deadline in mind as well as the optimal design execution.

What didn't work: 

• Well this is something I learned which is that the base needs to be sturdy.
• I think if we had more coil or perhaps more turns, the same speed of spinning would have caused a greater current. Also, from what I have learned about Electromagnetic Induction, I think more powerful and more numbers of coils and magnets would help induce more Voltage. 
• One issue we really ran into was finding a good way to coil the wires because it was really a lot of wire to handle. My advice on this for myself or anyone next time is to do it around some object like a strip of cardboard which is what worked for us. Also be sure to visually indicate which way you are wrapping or else you might forget. Lastly, do not wrap too tightly around whatever strip you use because we did that and it was a real pain to get off. 
• If I could do this again with more time, I might consider adding more wings to catch the wind in order to spin with more speed. 

Magnetism Unit Summary

Magnets and Magnetism:

Magnets:

The source of all magnetism is moving charges. These charges are spinning and moving inside an object and they congregate in groups called domains. The reason magnets are magnetized is because all of their domains are aligned. Domains are groups of moving charges that are grouped because they are all spinning in the same direction. When all of the domains align in the same direction, the object is magnetized. 

This is what the domains look like in a magnetized and not magnetized object:

 When an object is magnetized, it has a north and a south pole. The way you can tell which is which is by looking at the direction of the domains. In a magnet, the field lines(which indicate the direction the domains are facing) run South to North always. Here is a picture of field lines and poles in a magnet. 

If you were to place a permanent magnet very close to a table covered in tiny magnet fragments, the magnets would be attracted to the magnet and the result would reveal an actual visual of these field lines. It would look like this: You can see the magnets aligning with the domains of the permanent magnet and you can see the actual field lines. 

The poles of a magnet and the field lines help us to explain their attraction or repulsion. 

Opposite poles attract because when the the North Pole of one magnet is next to the South Pole of another, it is oriented so that the field lines of both magnets are going in the same direction. This is a helpful representation of this: (the arrows above the magnets indicate that they are attracted. Don't be confused, they do not indicate the direction of field lines). 

Similarly, Like Poles repel because when two like poles are situated next to each other as shown above, the field lines run in opposite directions. This makes it so that when they get close, the fields bump heads instead of cohering. 

Moving Charges Feel a Force in a magnetic field:

Another thing we learned about moving charges is that when they move perpendicular to a magnetic field, the feel a Force. 

There are two good examples of this in action. One is the northern lights. The northern lights are cosmic rays that are able to enter earth's atmosphere. Why do they only occur at the poles? Consider this image of the Earth's field lines:

When the charges of the cosmic rays are moving perpendicular to the magnetic field of the earth, as they would need to do to enter the earth at the equator, the charges feel a Force and are forced back into space. However, when the charges try to enter at the poles, they are moving parallel to the magnetic field. You can imagine a charge entering along side the lines at the top. This phenomenon that occurs at the poles is exclusive to the poles because anywhere else, the charges move perpendicular and are forced away. 

Another thing that we may apply this concept to is motors. A motor uses the force felt by charges in a magnetic field to create a torque. 

A motor consists of a battery which provides current to a current carrying wire that you would place near a magnet. The charges in the wire feel a force from the magnetic field of the magnet, and, if you strategically allow the force to be exerted, you can create a torque and spin the wire. 

A version of a simple motor like this looks like this: The loop of wire is scraped so that the force felt from the magnetic field is used to turn the loop rather that just shake it. 

By using the current carrying wire and magnet to move the loop of wire, a motor changes Electromagnetic Energy into Mechanic Energy. 

Electromagnetic Induction:

Electromagnetic Induction is a very important topic that we learned about this unit. Electromagnetic Induction uses a change in a magnetic field to induce a Voltage which causes a current. This is the converse of the way a motor works. Whereas a motor turned Electromagnetic Energy into Mechanic Energy, Electromagnetic Induction uses Mechanical Energy and turns it into Electromagnetic Energy. 

A common and useful example of where this is employed is at stoplights. At stoplights, there is a coil of wire in the asphalt. Your car has a magnetic field and when you drive over the coil of water, it changes the magnetic field (this is using Mechanical Energy). The change in the magnetic field induces a voltage and that voltage causes a current (this is the Electromagnetic Energy). The current caused is sent to the stoplight so that it knows you are waiting for a green light.  

You may recognize the loops on the road, they look like this:

The second and most important implementation of Electromagnetic Induction is in Transformers. You may recognize a transformer as that box on your computer charger, or the structure between power lines. The Transformer is used to either step-up or step-down voltage. For instance, a wall socket always has 120V, however your computer may need less (like 10V) that that so the transformer will step-down. 

The transformer relays on the same concept: Transformers consist of coils of wire that have AC current in them. This current has charges moving back and forth which changes the magnetic field. The change in magnetic field induces a voltage.

Here is where the process changes a little. The Transformer consists of two coils of wire, each with a different number of loops. Faraday's law is a law that states that the number of loops is directly proportional to the voltage, so if you want to step-up the Voltage you have to increase the number of loops in the Second coil and vise versa for step-down. The first coil(generally the one that hooks up to the outlet) is called the Primary. The one connected to the device is called the Secondary. 

So, when the voltage is induced in the Primary, by proximity it induces a voltage in the Secondary but because of the different number of loops, the voltage is either smaller or larger than before. In this system, Power is conserved so we use this equation to help us find Voltage and number of loops in each:  

#loops in 1/Voltage in 1 = #loops in 2/Voltage in 2

That is our Unit on Magnetism, Thanks for reading!

Motor Lab

Motor Blog

The way a motor works is fundamentally is it uses the force that the current carrying wire feels in a magnetic field to create a torque and make the coil spin.

Here is a picture of what a simple representation of that motor looks like:

The Battery is connected to the current carrying wire, and by completing the circuit with the wire, current runs through the wire.

The Magnet is placed on top of the battery. It doesn't actually matter if it interacts with the battery, in fact, it is used to create a magnetic field for the wire to feel force from. If you can imagine, the field lies in between the coil and the magnet.

The Current Carrying Wire is used because the electrons inside are moving around and feeling force from the magnetic field. This way, the coil can move.

The Coil is coiled and not just straight across because the reason it moves is by current running through the coils, so the more the current moves, the more the coil moves.

The way the motor actually moves is because the current carrying wire feels the force, yes. But you also have to encourage the spinning to direct the force in a circular way. The current carrying wire is coated so that you have to scrape off the coating on the parts you want to feel a force. For a spinning coil motor, you have to scrape the top of both sides. This means when your coil is facing you so that you can see through the loop, scrape the top of the wire on both sides of the coil. You can scrape the bottom as well as long as you're consistent.
We have to do this because the direction that the magnetic field goes is South to North, so the field lines run up. This is a picture Ms. Lawrence drew in her motor video which is very helpful!

As you can see, the way the arrows point (aka the force the current carrying wire feels), it is always pushing on the coil. If you only do the top part for scraping, then the force is always pushing it so that it turns but dosen't just move side to side.

I made one of these simple motors in class. Here is a video of it spinning/working:


Some uses of motors like this in a more complicated, sophisticated form are: In a car, or in a hairdryer or in a clock or in a robot.

Electricity Unit Summary

Electricity

The fundamental parts of electricity are charges.

Electrons usually carry a negative charge and protons carry a positive charge. Being that things are made out of protons and electrons, things are charged. If something has the same number of electrons as you do protons (same number of positive and negative charges) then it is neutral.



When an object is polarized, it means that one side of the charges have moved to one side of the object. That is, all the positive charges would have moved to one side, and the negative to the other so that one side of the object is positive and the other is negative, but the object is still neutral.

One kind of charged electricity we talked about was Static Electricity. 
There are three ways to charge something:

1.) Through Friction (by rubbing two things together)
2.) By Polarization. The way this works is that you bring an object over that is of either - or + charge and it attracts the opposite charge and repels the like charge. An example of this is when a balloon sticks to a wall. First you charge the balloon (-) using the aforementioned friction, then when you put it on the wall, the + attract and because the distance is less that the distance of the - charges repelling, the force is greater and the balloon sticks.
3.) Through Induction. Induction is similar to polarization in that you basically use a charged rod in the way of the balloon to polarize and object and then separate the two sides and you have two charged objects.

This image helps visualize it a little:

I mentioned before that a balloon sticks to a wall because of the distance between charges. This is because of Coulomb's Law which is....

F=kq1q2/d^2

Here the k is just a constant, and the two q's stand for charges. The force and distance are inversely (square) proportionate, so when the distance is lesser the force is greater and vise versa.

The Force that is push and pull of charges is caused by Electric Fields. - which is the area of influence (push or pull) around a charge. Basically, the energy is stored in the electric fields. 

The way you draw the electric field of a charge is by drawing arrows out from it indicating which way a positive charge would go. here is an example:

Electric Fields facilitate Electric Shielding. This is the reason we have metal casings around electronics, it protects the charges from being influenced by outside charges in the world. It works because the metal shield pulls the charges inside all around, and the pulls from one side cancel the pulls from the other, and the charge inside feels no force.

We did a podcast on Electric fields, here it is:



So, the Electric Fields hold the energy of the charge, the potential of this is called Electric Potential, which is the potential energy per charge. We call this Electric Potential Volts. 

We represent that as this formula:            V=PE (potential energy)/ q (charge)

When we have a difference in Volts, it is called Voltage. Sometimes we have something with high volts and something with low volts and the energy wants to travel from the High voltage to the Low.
This flow from high to low completes a circuit, and when the circuit is complete, then the energy is compelled to run through.

This flow of energy is called Current (represented with an I).
Ohm's Law defines the relationship between Current and Voltage:

I=V/R

The I is current and the V is change in Volts, but the R stands for Resistance. which are measured in ohms (the symbol for this is an omega sign in greek).
Resistance is something that is put in circuits to regulate the current despite what the voltage is.
Every normal outlet has a voltage of 120V, but appliances change their receptive currents for whatever the appliances needs are by adding resistors.

When you look at the equation, you can tell that the resistance and current can change but keep the voltage the same. The same is true for current. You can keep current the same, but still make an appliance more or less dangerous by increasing the resistance. for instance 5/10 and 2/4 are both equal to .5 (that would be the unchanged current), but the volts are 5V in one and 2V  in another by increasing the resistance.

The first box on this website explains resistance well and you can enter numbers to play around with how they all relate.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmlaw.html

There are two types of current: AC and DC
AC is alternating current, that is when the electrons move side to side as energy
DC is direct current, which is when they move forward.

There are a couple of things that affect current like
a.) thickness of what is traveling through. Thicker=more conducive
b.) Temperature- cold is better
c.) length- a short wire/tube is better

When we talk about actual circuits in places, often the circuits are parallel. What this means is that there are several appliances hooked up to a voltage source, and while they are hooked to the same source, they can operate autonomously. The alternative to this is a series circuit, which is set up to where each thing hooked up gets its current through the previous thing so, if one goes out they all do. Think christmas lights.

This is a great picture of what that looks like:

A parallel is preferable because you can turn one thing on without having to turn everything on. But, because on a series, everything is connected to the same line going to the source, when you add something, the current goes down because they are sharing and the resistance goes up. But in parallel, when you add one, you must increase the current to accomodate. 

To make sure that the current does't get too high and cause a fire or something horrible like that, we have fuses and circuit breakers. These will detect that the current is too high and break the circuit so that it isn't complete and the current won't flow 

A fuse is the same as a circuit breaker in purpose, but simply a different mechanism. 

to figure out the power you are using, you use the formula:

P=I/V which is measured in kw(kilowatts)/hr. 

To figure out how much it costs all together, you do this:

Power x hrs x $ per hour

And that's what we learned about Electricity!

Mousetrap Car Reflection

For the last few days, we have been working on making a car using a mousetrap to propel it. Our goal has been to make a car that goes five meters, and preferably with speed.
Yesterday we raced our cars, and here were the results:


Our car went an average velocity of .60 m/s.
(velocity = distance/time)
Distance: 5m
Time: 8.2 seconds
We came in last for our class as far as I know.

Here is a picture of the car we made:

and here is a diagram of it to make the individual parts clearer to see for reference when reading the following reflection.

Here is a video of our trial of our car going:


Reflection:

a.) Newton's First Law sates that an object in motion stays in motion unless acted upon by an outside force. In this case, the outside force is primarily Friction. The friction is needed to get the car going, you must utilize it to get it from going to not moving to moving. But you don't want so much that it also makes it go from moving to not moving.

Newton's Second Law states that Acceleration = Force/Mass. For this, you need a large Force which is the spring to provide the force to cause acceleration. Too large of a mass, however, would lower the acceleration, but you must consider that the mass contributes to friction, so you do need some.

Newton's Third Law states that every action has an equal and opposite reaction. In this case, the most relevant action/reaction pair is Wheel pushes on ground, ground pushes on wheel (you can see this drawn on the diagram above in green). The Force that is a part of the work that the wheel does when pushing on the ground is the Force causing acceleration. As we know from the previous two laws, that Force is important to how quickly the car accelerate, and also the friction of that action is important in starting the car quickly as well.

b.) The main part of the car that relied on Friction was the wheels, specifically the part that made contact with the ground. This friction was the Force that acted on the car so that it could go from not moving to moving. the more friction there was there, the easier it was for it to go from not moving to moving. For this friction, we wanted it to be more than just the edge of the CD because that did't have much friction. We instead put some electric tape in the edges so that it would have more friction. We didn't want to have too much friction there either or else it would slow down the car as well (be the force that made it go from moving to not moving quickly as the car lost speed). We thought the electric tape would be a good balance. Another part of the car that valued friction was the place where the string coiled around the axel. the more friction this part had, the faster the string would spin the axel as it unraveled. We did not have the time or wherewithal to tinker with this part, but I imagine it may have made our car go faster.

c.) We decided to choose a medium sized wheel in our CDs. We did not think this through particularly well, however, we figured that moderate was the best way to go for this project. It turns out we were right to assume because Bigger wheels actually crate a bigger lever arm which means there is more torque. However, it cannot just be as big as possible because the bigger it is the more rotational inertia it has which will make it more reluctant to rotate. So a medium size like CDs accommodates both the hinderance and the advantage of wheel size.

d.) The Energy of the car is put in as we pull the lever arm/ set the mousetrap, and it is stored in the spring until you release it. The energy stored in the spring is Potential Energy. Once you let the spring spring back, the Potential Energy turns into Kinetic Energy. This Energy is conserved as it converts. For instance, if we knew we stored 100J of Potential Energy in the spring when we pulled it back, then at the end of its route, the lever arm then has 100J of Kinetic Energy. In our car, we had a wooden lever arm that was attached to the mousetrap, when we pulled it back, we coiled the string attached to it around the axel in the back. When we released the lever arm, the potential energy converted to Kinetic Energy as it swung back towards the front and spun the wheel as it gathered kinetic energy.

e.) We First Knew that we didn't want the wheels to be too heavy because having more mass would mean there would be more rotational inertia. This would make the wheels reluctant to rotate, and thus reluctant to move. We also wanted to make the torque of the wheel (the radius) fairly big to make the rotational inertia lower. When we make the lever arm bigger, we would make the force needed smaller. But because we didn't want it too big because of the aforementioned inertia problem. SO we got a medium size wheel. Theoretically, the wheel is going to be spun the same amount of times every time we pull the spring back and let it loose. So when we have a larger wheel, it will cover more distance in the same rotation which is another reason to make the wheel a little bigger.

f.) We cannot calculate work that the spring does on the car because the work it does is not parallel but rather perpendicular to the distance the car goes. The force it does goes towards the ground, and the distance the car travels is forwards. In the same vain, The potential Energy that gets stored in the spring when we pull back gets converted into kinetic energy, but that energy does not go into propelling the car forward because the Force that is in the Kinetic Energy is not parallel to the distance either. We can't calculate the force that accelerate's the car because the Force that accelerates the car is not related to the other equations we do have the information for. So we cannot put the thing we do know about how it went forward, the distance, and find the force because we cannot use the work or KE equation as they are not parallel.

Reflection: 

a.)   Our initial design was fairly similar to our final design. We had to change many things, such as the lever arm and the string, but they were not drastic design changes we just had to make them better. If we could do the project again, the design would change, but I think we mostly adapted our design in the interest of time. We did look at other people's cars and add tape to the edges of the wheels for friction and we also stabilized our wheels fixed to the axels instead of loose around them by the suggestion of Veronica and Alex.

b.) One of the major problems was that it simply did not go far enough. The spring did not pull our axis like we thought it would when we first tested the car. We first realized that we hadn't put both of the little activators that stuck out from the spring on top of the lever arm. So when we did that we basically doubled the PE. That really helped. Then we also shortened the string and lever arm and finally got it to go further. Also our body was very flimsy as we tinkered with it it would bend on accident so we had to tape a wooden stick to it on the bottom and top so that it would be more stable and we wouldn't lose the energy in the spring going into bending the base.

c.) I would make the car longer and thinner and out of sturdier material. I would take more care with the axel wheel relationship because ours was sloppier than I would have liked and I think we lost a lot of energy there. Also make better use of the leveler because ours seemed wobbly. I think I would also try to only put friction on the pack wheels which are attached to the string.

d.) I might take more care with the preliminary steps to ensure that I was less likely to have to repeat certain parts because they were not done well the first time. In that same thought, I should worry much less about time and not feel rushed. Haste makes waste. Also some thought into which design to choose would be helpful because we sort of chose the first one that looked good. And also get materials in on time.

Work Unit Summary

This Unit we studied Work and some other concepts pertaining to it.
First we learned...

Work and Power:

Work = Force x Distance 
Work is measured in joules

The force and distanced used to calculate the work you do on something must be parallel. For instance is a box weighs a certain number of Newtons(upwards), and you take it across the room(forward), then you don't do work on the box.

Work is fairly similar to what you may think it is. The only misleading thing about our idea of work is that sometimes we may feel as though we are putting more or less work in when the work is actually the same.

One way it is misleading is that you may get tired doing work faster and thus think you have done more work. This isn't more work, it is more power.

Power is the time in which you do work. Power is measured in watts.
(Power = Work / time)

So, if you do something faster an end up feeling more tired, you just used more power, your work probably didn't change.

Note: 746 watts = one horsepower.

We then learned that Work is also related to Kinetic Energy:

Kinetic Energy is basically energy that a moving object has. 
the formula is: 

KE = (1/2)m(v)^2

So, you can calculate the KE for anything that you know has mass and velocity. (an object that is not moving does not have KE. Neither does an object with no mass.)

What we learned is that the change in KE is equal to Work
change in KE = Work

Often, we will calculate the change in KE in an object that speeds up or slows down over a distance(the velocity changes). We can jump between Work and KE(and then power if we know the time) by subtracting the final KE from the initial KE and then finding the Force by plugging it into Work = Force x Distance using the distance it changed KE.

Once we learned about Kinetic Energy, we learned about Conservation of Energy:

We learned that, when an object moves(or doesn't), it does not lose energy. The energy may be lost to heat or sound or light, however it is all accounted for. You also do not add Energy. 

An example is when an object is swinging on a string. When it is at the top of it's path(and it may be a t rest), it has a lot of Potential Energy but no Kinetic Energy. When it swings down, it starts to lose potential energy and gain Kinetic Energy until at the nadir of the path, it has a lot of Kinetic Energy and no Potential Energy. This relationship, in fact, is equal and opposite. 

change in KE = change in PE

You could relate this to the law of conservation of momentum because in a given situation(like an airbag in a car), you could use the fact that the change in momentum/energy is always the same to determine the factors that increase or decrease your injury in a car crash. 

With these added equations, we add on to the amount of steps we could use to go from, say, PE to Work. We could use PE = KE, and then use KE = Work to find, say, distance or force. 

To Apply these to actual actions, we talked about Machines: 
Specifically, simple machines.

Three types of simple machines are:
a ramp, a pulley, and a jack(for a car).


The way Machines work is they increase the distance over which the work is done so that the force is decreased and it feels easier. This is a way in which what we are doing can feel deceiving because we may be tempted to say that the work decreases because it feels easier. However, it is rather the case that

Work in = Work out
F(D) = F(D)

For instance, a ramp with increase the distance of the work you put in which makes the force you put in less. However, it still equals the same work out regardless.

We did a podcast on Machines which includes some helpful examples about how machines work and how efficient they are. Watch below to learn more.



Thanks for reading!