Item NG080003: As a clay ball falls and hits the ground, the total amount of energy in the system stays the same because the decrease in energy due to the clay ball moving closer to the ground is equal to the increase in energy due to the clay ball and the floor getting warmer.

A boy holds a ball of clay above the floor.  He lets go of the clay ball, and it speeds up as it falls to the floor.  The clay ball flattens as it hits the floor and remains flat.  When the clay ball hits the floor, the ball and the floor get a little warmer.  (Assume that no energy is transferred between the clay ball and the air or between the floor and the air.)

As the clay ball falls and hits the floor, does the total amount of energy in the system (the clay ball and the floor) increase, decrease, or stay the same?  Why?

  1. The total amount of energy in the system increases because the clay ball and the floor are warmer, and therefore, have more energy.
  2. The total amount of energy in the system decreases.  Although the energy of the clay ball and the floor increases as they get warmer, the energy of the clay ball decreases by an even greater amount as it moves closer to the ground.
  3. The total amount of energy in the system stays the same because the decrease in energy due to the clay ball moving closer to the ground is equal to the increase in energy due to the clay ball and the floor getting warmer.
  4. The total amount of energy in the system stays the same.  Even though the clay ball and the floor are warmer, being warmer is not associated with the amount of energy an object has.

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