Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: 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
thermal energy that is released into the atmosphere.
thermal energy.