Lab 3: Conservation of energy
In this experiment, we assumed the equation: mgh=(mv/t)(v/2)t=(1/2)mv2 This is an equation that describes how energy is conserved for a falling ball. On the left hand side, the quantity mgh is the force on the ball times its height h above the ground before it was dropped. We call it the gravitational potential energy of the ball before it was dropped. On the right hand side is a quantity (1/2) mv2 which is called the kinetic energy of the ball just before it hits the ground. We interpret the = sign to mean that the gravitational potential energy of the ball before it fell was converted into an exactly equal amount of kinetic energy which it had just before it hit the ground. Therefore, for a falling ball, two forms of energy, kinetic and gravitational potential, are involved. The sum is: Total energy = gravitational potential energy + kinetic energy. Energy stays the same during the motion, but at the beginning of the fall it is all gravitational potential and at the end it is all kinetic. In between, though we did not prove it, the gravitational potential energy gradually decreases while the kinetic energy increases to keep the sum constant. The fact that the sum is unchanged is what we mean by conservation of energy in this case. As we did in the previous experiments, we place the aluminum track horizontally on the desk and fix the pulley on one end of the track. We put the cart on the track with the strings attached to it. At the other end of the string is the mass hanger where we added masses in that. As the weight of the masses will pull the cart to move on the track we could measure the velocity of the cart. With the computer data analysis software, we found the velocity of the cart or hanging mass at any point in time. Then we use the formula EK= (1/2)mv2 to calculate the kinetic energy of each object separately. There was no change in the gravitational potential energy of the cart – if the track is level,...
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