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on the word document it says that there isnt anything on it. -v

Veronica West, Alison Shapiro, Caroline Ingalls Physics, 3 April 16, 2012 Physics in Action

There are three types of energy, gravitational potential energy, kinetic energy, and elastic potential energy. The two main types are potential and kinetic energy. Potential energy is stored energy, meaning the object has the potential to move. Kinetic energy is moving energy. To move, the object uses work. The work that it takes to move to object is equal to the applied force and the distance it travels. The work must be enough to start moving the object and to keep on moving. When moving upward, the object has the most kinetic energy as soon as it leaves the ground after the force is applied. As it keeps moving up, the kinetic energy decreases and the potential energy increases. When the object gets to its highest position, which is when it has the most potential energy. On the way down, the potential energy decreases and the kinetic energy increases as it gets closer to the ground. The total energy always stays the same. When an amount of energy increases or decreases, the other amount of energy does the opposite of it. So when the potential energy increases by 4, the kinetic energy decreases by 4. In our pictures, we show a marble rolling up and down a track shaped like a U to show energy. When the marble starts at the top, it has only gravitational potential energy because it is not moving so it has no kinetic energy. Also, it is at its highest point, and when it is released it will roll downhill. It has stored energy from gravity making it want to move down. When the marble is released, it loses potential energy and gains kinetic energy as it moves towards the ground. When it reaches the bottom of the track, the marble has only kinetic energy because it is no longer above the ground and gravity no longer affects it. As it starts to move up, it loses kinetic energy and gains potential energy because it is now off of the ground. When it gets to its highest point, it has all potential energy and it starts all over again as it goes down. The marble goes a shorter distance up the track each time just because of friction. If there was no friction it would always go the same height each time. In the activity, we measured how much force and energy a person needs to do a vertical jump. First, we converted their weight to Newtons and found how many meters their center of mass was from the ground when they were in the ready position. Then they stood on their toes as if they were going to jump but didn't leave the ground, and we measured the distance from their center of mass and the ground. Then we subtracted the two to see the vertical height that their leg muscles had to provide force to lift them up. Then the person jumped as high as they could and they recorded how high their center of mass was from the ground. Then we had to subtract the peak position from the launch position to find the jump height. Then we used the data to find the total force provided by the leg muscles. The work that the person did to lift themselves from the ready to the launch position was an increase in potential energy. It also provided the jumper with enough speed to keep moving up which was kinetic energy. As they went up the potential energy increased and the kinetic energy decreased. As they went down, the potential energy decreased and the kinetic energy increased.

Center of mass is the point at which all the mass of an object is considered to be concentrated for calculations concerning motion of an object. It is basically the point of an object where it has the best balance, so it is where the object balances the best because it has the most control over all of the mass of the object. For equal sized objects, meaning all of the mass is equal distance from the center, the center of mass is in the middle of the object. For objects that are weighted differently, the center of mass will be somewhere on the object where the weight of the mass on both sides of the object is equal. The center of mass is what decides how the object moves. If you push it straight on, right on the center of mass, the object will have the most control and go straight because that is where all of the mass of the object has the most control. If you push it more towards one of its sides, the object will spin the opposite way and not have very good control. It was pushed somewhere where the mass was lopsided, so the force applied was not equal throughout the object, causing it to not have good control and spin wildly. The center of mass can also be called the balance point, because that is the place on the object where it balances the best. The balance point is where all of the mass is equal on both sides so that is where it will stay and balance the best. Three dimensional objects have a center of mass inside of them because that is where the mass is equally distributed all around the center of mass point. In order for an object to fall over, the center of mass point has to pass outside of the object’s frame. That is why shorter people have to be pushed more to fall over than taller people; it takes a longer distance for their center of mass to pass outside of their frame than a taller person’s. To show center of mass, we took a video of Caroline balancing a pencil on her finger at the center of mass point and her sliding her finger over so it is off balance and it toppled over. When her finger was in the center of mass on the pencil, the pencil stayed because the mass was equal on both sides. When she moved her finger to the side, the mass became unequal and lopsided so it tipped and fell over. It only stayed on her finger because that is where she had the most control over all the mass of the pencil. When she moved her finger to somewhere that did not have control, it tipped. In the activity, we had four objects and we had to find the center of mass for all of them. To do that, we estimated where we thought the center of mass was on all of them and we marked it with a dry erase marker. Then, we took a string with a weight on it and attached it to three holes on the object, let it hand down, and marked where the strings went. Where all three strings met, that is where the center of mass was. When we tried balancing the object on that spot we were able to because that is where the object had the most control over all of its mass.

thats just what i did