Conversation so far:
when does a roller coaster train have the highest potential energy
Gravitational potential energy is greatest at the highest point of a roller coaster and least at the lowest point.
what is the highest point of a roller coaster
The first hill of a roller coaster is always the highest point of the roller coaster because friction and drag immediately begin robbing the car of energy
where do cars in roller coasters move the fastest
Cars in roller coasters always move the fastest at the bottoms of hills
what does friction do to roller coasters
Friction turns the useful energy of the roller coaster into heat energy

Question: what puropse does heat serve
Self-contained rewrite: what purpose does heat serve for roller coasters