Simple Harmonic Motion

A child jumping up and down is not an example of simple harmonic motion. I'm not going mad, right? Because I've just spent an hour arguing with my physics teacher who thinks that it is. No change in acceleration = no change in force = force isn't proportional to displacement

There is a change in acceleration, or the kid wouldn't be able to alternate between going up and going down.

While the kid is in the air though, there is no change in acceleration, so you're still right.

Perhaps if the child were jumping on a tightrope walk or a trampoline it would be more of a harmonic motion, because the negative amplitude must be the same as the positive?

>>3
As soon as the child isn't touching anything anymore, gravity is the only significant force. Gravity is ~constant, and therefore cannot be proportional to displacement.

acceleration is also a change in direction.  This is how stuff like uniform circular motion works where the velocity is constant yet there is still a force because there is still an acceleration(the change in the direction, remember vectors).

This would have to be a perfectly like bouncy kid though, I mean it is a VERY bad example of SHM because when you imagine a kid in real life he jumps, hits the ground and stops, then uses more internal energy from his cheerios to launch up again and burns calories....  shitty shitty example.  Kid on a trampoline would be better,  but still shitty compared to the simple block on a spring idea

>>1

your physics teacher is an arse. acceleration is supposed to be proportional the displacement, and always directed towards the centre point of equilibrium. that clearly does not happen with a kid jumping.