Q3.
When you pedal a bicycle on a flat road, your muscles supply energy. In what forms does this muscular energy appear as you ride?
Answer
The chemical energy in your muscles is converted into these forms:
- Kinetic energy of the bicycle and of yourself — while you are speeding up. Once you ride at a steady speed this stops growing.
- Thermal energy — the largest share. Work done against friction at the axles, the chain and the tyre–road contact, and against air resistance, heats the parts, the road surface and the air.
- Sound energy — the small noise of the chain, the tyres and the wind.
- Thermal energy inside your body — muscles are not perfectly efficient, so you warm up and sweat.
On a flat road there is no gain in potential energy (h does not change)
At a steady speed there is no gain in kinetic energy either
So: energy supplied by muscles = work done against friction and air resistance
= thermal energy + a little sound energy
At a steady speed there is no gain in kinetic energy either
So: energy supplied by muscles = work done against friction and air resistance
= thermal energy + a little sound energy
Why it happens: at a steady speed the net force on you is zero, so your forward push exactly balances friction and drag. Every joule your muscles put in is immediately carried away by those opposing forces, which do an equal amount of negative work. Stop pedalling and the bicycle coasts to a halt, because the drain continues while the supply has stopped.