Unit 6 Reflection

In the latest Chapter of Physics, we studied Work, Power, and Energy.

Work is the measure of force that is applied to an object over a distance that is parallel to the said force.  The most important word in the preceding sentence is PARALLEL.  If the force is not parallel to the distance it is being moved, no work is generated. For example, the act of a person walking up a flight of stairs generates force, while the act of carrying a book across a classroom does not.  In the case of the book being carried across a classroom, the force of the book is downward, while the distance is from left to right, meaning that the two are perpendicular, and no work is generated.  The equation for work is:

                                                                  W = F x D
Where F = Force and D = Distance.  For example, if a 100 N man runs up a 7 m high staircase, he exerts 700 Joules of work.  In terms of work, it does not matter whether the man runs or walks.  His speed does affect his Power, however.

Power is essentially a rate of work.  The equation for Power is P = Work Done/Time Interval.  Therefore, if you are to exert 500 Joules in 5 seconds, your power is 100 watts.  In the following video, let's pretend Rocky weighs 100 N, and the stairs are 30 meters high.  He would exert 3000 Joules of Energy.

He also runs up the stairs in 8 seconds.  Therefore, we would use the equation P=W/t and substitute, leaving us with P= 3000/8 and find that he exerted 375 watts of power.  That's why he is a beast!

The next item we learned about is Gravitational Potential Energy.  The equation for potential energy is PE=mgh, or if you know the force, it is PE=Fh.  The h is significant because it stands for height.  Height is the most important aspect of potential energy.  This is because the high the object is, the more potential energy it has, and ultimately the more kinetic energy it can have.

Kinetic energy is the energy found in moving things.  The faster something is moving, the more kinetic energy it has.  Kinetic energy is proportional to work because of the equation Change in Work = Kinetic Energy.  The true equation for KE is KE=1/2mv^2.

As an object loses potential energy, it gains kinetic energy.  This is due to the Law of Conservation of Energy.      This law is what inhibits the operation of roller coasters.  Have you ever noticed that the first hill is always the tallest?  This is because that first hill gives the coaster alot of potential energy, which means it will be converted to alot of kinetic energy, giving the car enough speed to get through the rest of the track.  Watch closely on this roller coaster:

It is easy to see that the first incline is the tallest, and gives this ride alot of speed for the rest of the track.You can literally feel the physics!

The next topic we discussed was machines.  Machines are designed to help us exert less force and get more force out.  The most simple machine is a pulley.  Pulleys are designed to decrease the force while increasing the distance to increase the force outcome.  Watch how Jack and Jill use a pulley to pull water out of a well in the following video:

You can know just how well a machine is doing its job by finding the efficiency of it.  To find the efficiency, you simply use the equation, Efficiency = work done/work expected and convert the answer to a percentage. It is impossible to have a machine with 100% efficiency because energy is always lost as heat or friction.

Reflection:
Overall, this unit was not too challenging.  My problem solving skills did not suffer to much because most of the equation are easy to remember and use.  I found the need often to be very specific in my answers, because there are many trick questions in this chapter.

Final Mousetrap Car Blog

In the end, our car clocked in at an impressive 0 m/s.  However, I still learned oceans about physics from this project.  I also learned good problem solving skills that I will need later on in my life.  Here are the physics of the mousetrap car that I learned:

Newton's Laws can be applied to this car.  Newton's 1st law, which states that an object in motion will stay in motion until an outside force acts on it (and the converse for an object at rest), means that if we decrease the possibility for outside forces to interact with our car, we will increase its odds of reaching the finish line.  Newton's Second Law states that Acceleration is proportional to Fnet and inversely proportional to Mass, therefore, the more we decrease the mass, the better the acceleration of the car will be.  This led us to use the lightest possible materials, such as wooden skewers and paper towels.  Newton's Third Law states that for ever action there is an equal and opposite reaction.  We applied this aspect of physics to our lever system.  We knew we had to decrease the friction between the string and the axis, so we tied the string to the axis in a quadruple under over knot, and taped it as tightly as possible.

Two types of Friction that were present in the making of this car were air resistance and surface friction.  Air resistance is difficult to change because the faster the car goes, the more air resistance there is.  However, we could decrease air resistance on the car by decreasing the surface area.  We did this by taping down all loose paper towels to make sure there was nothing that could spread out and increase the surface.  We used surface friction to our advantage.  Initially, CD's seemed like a bad choice for wheels.  However, once we covered them in duct tape and increased the friction on the ground, the car moved very smoothly.

It didn't take much thought to decide which wheels we would use.  We knew CD's would be a great choice because they have a very low rotational inertia due to the fact that the mass is evenly distributed throughout.  This meant that they would be easy to get moving.  Also, the fact that they are larger than, RC Car wheels, for instance, means that they have more mass, giving them more rotational velocity.  We chose to use 4 wheels simply because it was all we had room for.

The Law of Conservation of Energy (Force in X Distance in = Force out X Distance out) played a large role in the making of the mousetrap car.  We knew that if we made the lever arm very long, in addition to increasing the force, we would see a long distance output and strong force output.  It is for this reason that we decided to make our lever arm out of 3 wooden skewers taped together tightly.  This gave the lever arm strength and length, increasing our work output twofold, and making the car very efficient.

The work done by the spring was impossible to calculate because we could not calculate the Force (weight) of the spring, and Work = Force X Distance.  Calculating the force of the spring would involve removing the spring and actually weighing it, which would render our mousetrap unusable.  We also cannot calculate the amount of Potential Energy on the spring because PE = mgh, and the height of the spring is minuscule throughout its path, and changing very quickly, making it very hard to take into account.  Thus, we cannot calculate the Kinetic Energy on the car.  We cannot calculate the Force the spring exerted because we cannot find the mass of the spring to use the equation A = Fnet/m

The final product of this project was very different from our original design.  The biggest difference was that  our wheels were more stable than they ever were.  We had to apply many feet of tape to the car to make this change. We still encountered many problems, for example, the wheels did not have enough friction on the axis  to move as quickly as the axis moved.  Because of this, the wheels simply wouldn't move when we set the mousetrap off.  This problem never got fixed, but it was probably due to the makeshift axis.  In the future, I would like to have more time for planning, and also more supplies.  I feel like I entered this project blind as to how to make one of these cars.

Mousetrap Car: Day 2

The most important step we took going forward was to get new supplies.  Here is a list of our new supplies:

• CD's- These will function as our wheels.  Since the mass is evenly distributed throughout, they will have less rotational inertia, and will hopefully go quite fast.
• Wooden Skewers- These are thin enough to fit into our eye hooks, so they should work well as axis.
• Paper Towels- We will use paper towels to wrap around the skewers, which will fill in the gap between the inside of the wheel and the skewer.
• Tape (lots of it)- We will use tape to secure not only the paper towels to the Skewers, but also to secure the wheels to the paper towels.
• A rubber band- Instead of a string to act as the lever arm force for the car, it should provide extra force since it is stronger.

We also faced new challenges in building our new design.  Here are a few:

• The skewer would not stop rotating from left to right: To fix this, we put heavy layers of tape on the skewer in between the eye hooks, to act as an anchor, and keep the skewer in place.  This worked very well.
• The CD's were touching each other: To combat this, we aligned the CD's so that the back wheels were farther apart than the front wheels.  This kept them from rubbing against each other.
• The rubber band would not move the car: We decided to switch our tactic and tape two skewers together to create a long lever arm.  Then we taped this to the lever on the mouse trap to create the lever arm system.  We tied a quadruple over-under knot on the lever, then taped over that for safety.  We did the same on the back axis.
• The Lever Arm came off of the mouse trap lever: To fix this, we simply applied more tape and made it sturdier. 
• The lever system did not move the car: We still need to find a solution to this problem. We believe that the wheels are not sticking to the axis, therefore when the axis turn very fast, the wheels cannot keep up and simply stay put while the axis turns quickly inside the wheels.  To fix this, we may need to completely change the way we keep the wheels on the axis.  

Mousetrap Car Day One

Due to some severe communication issues with my partner, the project did not go as planned for the first day.  We found ourselves without key parts to build the car.  However, we put our minds together and began work on a new design, one much simpler than our original plan.

Since we were at a loss for parts, our only step forward was:

• Drill big eye holes into the ends of the mousetrap.  These will hold skewers, which will server as our new axis. 
• The skewers will be centered in the eye holes and then we will apply cotton swabs to each side, these will work to keep CDs (not records) to the skewers.
• The reason we are not using Records is because they are too big, and it would be hard to set up the car without all four records touching each other and upsetting the path. 

It will be very important to  make sure the CDs are tightly fit on the axis.  This will help make sure that the car can achieve the maximum speed possible.  We will also need to put tape or some other source of grip on the CDs to make sure they have enough friction to propel forward.

In order to solve our biggest problem (not having supplies or time to get them), we will resort to finding materials around our house/room that can work for the project.   

Mousetrap Car: Blog

In order to build this mousetrap car, I will need the following items:

• 4 Vinyl Records-since they are large, and have a very low rotational inertia, they will function well as the wheels for the car.
• Mousetrap-provided by Mrs. Lawrence.
• 2 BIC pins (smooth kind) to use as axis for the wheels.
• Small balloons- I can use these to wrap around the wheels which will give them more traction.  I only need to apply them to the back wheels.  However, they can also be used to fit the inside of the wheel close to the axis.
• 4 eye hooks- These need to be big enough for the pens to fit through and be able to move, however, the pen needs to not movie in an out of the hooks.  Therefore I should devise a plan to keep the pen centered.
• String- This will be connected to the the back axis and the pen of the mousetrap so that, when set off, will propel the car forward.

This will be my construction process:

• Pull the ends off of the pins, as to make them hollow.
• Cut holes in the balloons, so they will fit over the wheels, to give the wheels more traction.
• Fit the eye hooks on the pins, firmly but not too tight.
• Make a hole in the frame of the pen, and thread the string through.
• Put the eye holes in the mouse trap like so:

• Insert front axis, (one without string).
• Wrap unused balloons around ends of the front axis tightly.
• Insert wheels onto axis.
• Repeat for back wheels