Question: Alicia gives her brother a push while he is seated on a swing. She finds that after a few seconds, she needs to push again to keep him going. The reason her brother slows down is because the mechanical energy is converted into

  Options: 
 A. potential energy that heats the air.
 B. chemical energy that moves the swing.
 C. kinetic energy which makes the swing slow down.
 D. thermal energy that is released into the atmosphere.
Answer: D