## Tuesday, January 25, 2011

### Energy at Six Flags!!

This unit in physics we studied Conservation Laws of Energy. We learned about how to use bar graphs as energy flow diagrams. Energy is everywhere, although the amount of energy never changes, the method in which the energy is stored changes. Energy can be stored as elastic, kinetic, gravitational, potential, and chemical potential. We defined energy transfer as work or W. We learned how to find work, power, kinetic and potential energy, and the work energy theorem.

I made a Glogster to help explain this unit more effectively:

## Sunday, January 16, 2011

### Round and Round and Round We Go!

This is what I learned about circular motion and gravity. I learned that in order for an object to be in any kind of circular motion, there needed to be some sort of centripetal force keeping the object moving in a circle. Whether the centripetal force is the friction between car tires and the road, or just the tension of a string swinging a ball, it is always there. I learned that the velocity is constantly changing when an object is in circular motion because the direction is always changing. I learned the Law of Universal Gravitation and how every object attracts every other object in the universe. I learned that the variable G is always $6.67x10^{-11}N.m^{2}/kg^{2}$. I also learned how to find the acceleration due to gravity in situations not on the earth's surface.
When we first started out this unit I had some difficulties understanding all of the concepts. I especially had trouble with figuring out which equation to use with the given information. It was very difficult for me to change equations in order to find different quantities. What I have found difficult about what I have studied is finding and using the sum of the forces equations when dealing with motion in vertical circles. I had lots of trouble figuring out how to use the sum of forces (sigma F) equations with the new equations we learned specifically for circles. The most difficult concept for me to comprehend was gravitational acceleration, specifically when we had to use ratios to find our answers. I eventually figured out how to use ratios in these cases and once I did everything became infinitely easier. What I found most simple was the whole concept of gravitational acceleration. The whole concept was easy to understand and made sense so it did not cause me much trouble.
My problem solving skills have definitely increased over the course of this unit. As usual, I started out the unit very confused and unsure how to solve most of the problems, but as I worked more problems and did the classwork in our notes, I became more confident. One of my weaknesses at the beginning was calculating the centripetal force when there is very little information given. Say you are in a car and about to enter a traffic circle with a radius of 30 m. You are traveling at 6 m/s and the mass of your car is about 300 kilograms. In order to find the centripetal force you would use the equation $F_{c}=mv^{2}/r$. Then you would plug in the information and you would get Fc=360 N. Now that seems fairly simple, but if you take away one of the variables and everything becomes much more complicated. I think the main thing that made this unit difficult for me was that for almost every single problem there was more than one step to find the answer and I would get confused on when to do what and how. Mostly all of the gravitational problems were fairly easy to comprehend. This unit has definitely helped me to better understand circular motion, gravitational acceleration and how forces are everywhere.

## Sunday, January 2, 2011

### Mythbusters: Physics Edition

In our physics class we created our own mythbusters episode to disprove some common myths about physics.

Myth 1: An object always moves in the direction of the net force exerted on it.
When first looking at this you think, well this should be true right? Wrong! When you take a closer look here's what you get:

For this experiment we are going to focus on the time the ball is actually rolling not when it is initially pushed. So when you look at the FBD of the ball while it is in motion you will see that the net force of the ball is actually backwards even though the ball is rolling forwards.

The net force would be ΣFx = -Ff but the ball is not moving in a negative direction, it is moving in a positive direction; therefore this myth is... BUSTED!

Myth 2: An object always changes its motion if there is a force exerted on it by other objects.
Again this seems pretty reasonable, but my team of mythbusters found a way to bust this myth too.

So in this experiment, the tennis ball hit the bowling ball while it was in motion. If you look at the FBD of the bowling ball at the moment the tennis ball hits it, you see that even though there is an applied force going in the negative  direction, the ball continues its motion unchanged. Although the ball might have slightly slowed down, we could not detect a detectable amount of change in motion in the ball.

Even though there is an applied force going in the negative direction, the ball continues it's path moving in the positive direction unchanged. This myth is totally BUSTED!

Conclusion:
Neither of these two myths was too big of a challenge for our superior team of mythbusters. We couldn't prove these myths wrong completely because we lack the proper materials but based on our data (what we saw the ball do) we can loosely conclude that these myths are busted.
People believe that an object always moves in the direction of the net force exerted on it because it sounds pretty reasonable. If you push a wagon, most likely the wagon will go in the direction you pushed it, it won't randomly start going sideways or backwards. But, in some cases, the ΣF is not going in the same direction as the object. People usually believe this myth because we forget the force of friction exists, this myth would be true if friction did not exist but there is friction in our world, therefore this myth is untrue. People will also believe that an object always changes its motion if there is a force exerted on it by other objects because again, it sounds reasonable. If you push that same wagon it usually will start moving in the direction you pushed it. But if the wagon weighs 600 pounds and you only weigh 90, there is not a good chance that you will be able to get the wagon to move. So if the applied force is significantly smaller than the object then the object will not change its motion. People just don't like to think about the special cases of things, mostly they will just look at it and think hey that sounds right and not try to prove it wrong to themselves to prove themselves right. People are lazy sometimes and sometimes people just say oh that sounds right and do not bother to try it out.