Question

I need some help on Newton's laws concept questions.
1)Using Newtons laws expain why you must push harder on the pedals of a single speed bike to start it moving than to keep it moving with constant velocity.

Answer 1

Newton's First Law states that an object at rest or moving at a constant velocity will remain in that state until acted on by a non-zero net force.

When you first start pedalling, you're getting that bike to go from rest to moving. That means you need to apply a large force to get this to happen (i.e. push harder on the pedals) and overcome the force of static friction.

Once you're already in motion, it's easy to stay in motion by the same law. If you start speeding up, slowing down, or turning, it will get harder because you're applying a non-zero net force to the bike.

Answer 2

Thank you! I was thinking along those lines but I think the "single speed" thing tripped me up for no reason.

Answer 3

Yeah I think they just threw that in so you wouldn't start thinking about changing gears, which makes everything more complicated.