Blog DANtheMAN

Last week I began building a mousetrap car with a friend of mine who was given the assignment as an extra credit assignment in their physics class. Their assignment is to build a car whose sole source of energy is a mousetrap. Whoever's car goes the farthest wins. While doing my research I found a few ideas centered around physics that appeared most important to the success of our car.

large wheel to axel ratio

Due to the small size of a mousetrap we only have the ability to rotate an axle a small number of times. To make the car travel as far as possible and to turn the few rotations we have into as much distance as possible we can make the wheels significantly larger then the axle. In this way every full rotation of the axle gives us a significant amount of distance.

Have Some Friction, But Only Enough

Whenever a problem involves using energy as efficiently as possible you will want to decrease friction as much as possible however in this problem we have to be sure we do not remove friction too much. In the case of our back wheels we are going to need a certain amount of friction to ensure that the wheels turn. The force friction between the wheels and the ground will provide a torque to drive our car forward. If there is not enough friction on the wheels they may began to slip on the floor. If this happens our potential energy is being turned into the rotational motion of the wheels but not the translational motion of the car. In other words, we are wasting our precess energy.

Long Fulcrum

Increasing the length of our fulcrum will have an effect similar to that of our large wheels. By increasing the fulcrum we can increase the total distance that we can turn the axle. The Fulcrum is the radius of a circle created by its rotation. If we increase is length we increase the circumference of that that circle and therefore increase the distance that we can pull the axle over. This in turn leads to more rotations of the axle and more rotations of our wheels giving us more distance.

Other then this a lot of it is simply tinkering around with your design until you have maximized your distance with the tools and materials you have. Try it out and see what you think.

Last week in class we began discussing gravity and the question came about as to what gravity is and what causes it. Gravity is an interesting part of science in that we can explain how it acts and predict what it will do but we it is not know what actually causes gravity. Just so we're clear, gravity is an attraction between two masses. All masses have a gravitational attraction to each other, even two people, although with small masses the force is essentially negligible. Although we don't know what causes gravity there are a few widely excepted theories of what its source is.

The Warping of spacetime

This idea can be hard to wrap your mind around at first. The idea is that universe is composed of a fabric that in the presence of mass warps around the mass. It is easiest to first picture this in twe dimensions. Imagine a sheeet being held flat above the ground. If a bowling ball was placed on the sheet, the sheet would deform, creating a cone like shape with the ball at its center. If you were to then take a marble and roll it on the sheet towards the bowling ball, it would fall into the the warped area of the sheet and it would have a result similar to that of one of those giant cone shaped coin collection tanks where the coin spirals around the tank. Assuming it had the right velocity, it would fall into a circular pattern around the ball, in other words orbiting around the ball. In the universe, the same thing is happening except the warping happens in all directions. More massive objects warp spacetime more so smaller objects always orbit around larger objects even though they also warp the space. This explains why moons orbit around planets which orbit around stars.

*If you do not understand this idea Brian Greene does a much better job of explaining it then I did in his book "The Elegant Universe"

The Kinetic Theory

The idea behind kinetic theory is that there are streams of tiny particles particles flowing throughout the universe in every direction. The theory suggests that masses will partially sheild eachother from these streams therefore decreasing the amount of force acting on the masses. This lack of force will then cause the two masses to have an attraction to eachother.

The Gravitron

This theory is similar to the Kinetic Theory. It suggests that gravity, similar to photons in the case of light, has a massless particle called a gravitron which causes the atraction. The theory says that gravitrons randomly float throughout the universe and when they strike a mass, they move the mass in the direction that the incident graitron came from while also randomly freeing a gravitron from the mass. This creates an attraction between masses while also explaining why larger masses have a greater force of gravity.

The Elves

This theory was recently suggested by my teacher Mr. Fullerton. He suggested that their could be trillions and trillions of tiny little elves every where in the universe. These elves would take ropes and attach them to every piece of matter in the universe and pull them towards each other creating an attraction force that we call gravity.

As we approach midterms it is hard to believe that we are more then half way through our journey in AP-C Physics. It has been a fun first semester. Taking the kinematics material much deeper then we did in physics B has been very intriguing. However tt seems like we have learned so much but at the same time I barely remember any of it. Even after I review formulas I have trouble recalling them during our four minute drills. There so much information on kinematics that it seems almost impossible that I'll be able to remember and recall it all when I have to. It looks like it's going to be a long week of studying until Thursday!

Over the past week we continued our studies of rotational motion, adding momentum and torque to our bank of knowledge. Unfortunately for me, i missed the first two days of the unit last week while I was out of town. As a result I have spent most of the week confused and out of the loop on practice problems. This weekend, I finally decided to help myself and learn the material. I did this by watching parts of two lectures done by MIT professor Walter Lewin. I watched both videos and took notes on the material and although lewin is no Mr. Fullerton, I was still able to gain a much better understanding of the material.

This past week my AP C class undertook an independent unit on impulse and moment. For the week we were given a lab, a multiple choice packet, and free response questions that we had to complete by the end of the week. Upon completion of our work we will be tested on impulse and momentum. This being the first time that I have ever been given as assignment like this it seemed interesting but it also seemed like if I was not on top of things in class I would have a lot of homework. Fortunately over the week we worked very efficiently and got most of the work done in class leaving just an hour or two of work over the week. Upon completion of this assignment I feel that I have learned more through this assignment then I would have through a week of simply lecturing. Through this project I was exposed to the material in several different ways and was forced to learn how to apply my knowledge to all sorts of problems. The individualised nature of the unit allowed me to focus my learning in a way that was most efficient for me, focusing on areas of confusion and quickly move through ideas I had a good grasp on. All in all, a very successful week in physics!