Energy Conversion — KE ⇄ PE

At the top the ball is momentarily still: all its energy is potential (mgh). As it falls, height is lost and speed gained — PE turns into kinetic energy (½mv²), reaching maximum speed at the lowest point. It then climbs the far side, KE turning back into PE. Energy is never created or destroyed, only converted. Friction doesn't break that rule — it just converts mechanical energy into heat, so the ball climbs a little lower each pass until it stops, with all the original PE now turned to heat.

• Try this: With no friction, watch KE and PE trade back and forth while the total bar stays fixed.
• Try this: Find the lowest point — KE is maximum and PE is minimum there.
• Try this: Add friction and watch the heat bar grow as the swings get smaller.
• Try this: Change the mass — both KE and PE scale with it, so the motion looks the same (mass cancels).