Hey guys, I need help with graphing acceleration to time for a bouncing ball (1 Viewer)

[bleakarcher]

Hey guys, can someone draw and explain this sort of graph for me?

 

[IamBread]

The acceleration? It's going to be g. not going to change.

 

[Timske]

horizontal line

 

[RealiseNothing]

I'm not doing moving about(I assume bleak is), but when the ball bounces, wouldn't it have to go down to a velocity of 0 then accelerate again as it bounces back up? And the bounce back up isn't 9.81ms^-1 is it?

Just curious.

 

[deswa1]

You are right that velocity changes as a function of time but acceleration is always constant. Regardless of where the ball is, the gravitational force downwards will lead to a gravitational acceleration downwards of 9.8ms^-1, thus acceleration is constant.

 

[RealiseNothing]

You are right that velocity changes as a function of time but acceleration is always constant. Regardless of where the ball is, the gravitational force downwards will lead to a gravitational acceleration downwards of 9.8ms^-1, thus acceleration is constant.

Ah I see, thanks for clearing it up.

 

[bleakarcher]

apparently it looks something like this

 

[bleakarcher]

Apparently, according to my teacher, as the ball strikes the ground and is sent back up again in that extremely small interval of time the acceleration is a large positive value if you taking gravity acting negatively. WTF?

 

[Timske]

The acceleration of the ball while it is in the air before it hits the ground is -g (downward) so when it bounces back up its going opposite direction to -g so its +g

 

[bleakarcher]

The acceleration of the ball while it is in the air before it hits the ground is -g (downward) so when it bounces back up its going opposite direction to -g so its +g

No it should still be -g as it is going upwards, thats why it comes back down lol.

 

[Timske]

oops.. velocity is positive going downwards and once it hits the ground velocity = 0 and backup - velocity. At the moment before it hits the ground
the balls has gained momentum during its time in the air so all this would be reflected upwards

 

[bleakarcher]

^ gtfo.

 

[Nooblet94]

The moment the ball hits the ground there's an acceleration in the upward direction, larger than the acceleration due to gravity. Apart from that it's constant.

EDIT: Just to clarify, that upward acceleration is instantaneous.

 

[someth1ng]

Just to clarify, that upward acceleration is instantaneous.

When a ball hits the ground, the ball gets squished giving it an upward force and so the acceleration isn't exactly instantaneous - just a small amount of time

 

[Carrotsticks]

The acceleration? It's going to be g. not going to change.

-g.

You are right that velocity changes as a function of time but acceleration is always constant. Regardless of where the ball is, the gravitational force downwards will lead to a gravitational acceleration downwards of 9.8ms^-1, thus acceleration is constant.

*ms^-2.

ms^-1 is velocity.

Apparently, according to my teacher, as the ball strikes the ground and is sent back up again in that extremely small interval of time the acceleration is a large positive value if you taking gravity acting negatively. WTF?

The forces acting upon the ball at all times is -g ms^-2 due to gravity.

However upon collision with the ground, a phenomenon called 'Elastic Collision' occurs, causing the momentary upward acceleration. I believe this is what your teacher was pertaining to.

http://en.wikipedia.org/wiki/Elastic_collision

 

[IamBread]

-g.

Depends which way you set as positive

 

[Carrotsticks]

Depends which way you set as positive

Indeed, though I think it would make sense to make the ground negative and the sky positive.

I don't understand all this riff raff about changing the positive direction unless it significantly makes computations easier (like in Extension 2 Resisted motion problems).

 

[IamBread]

Indeed, though I think it would make sense to make the ground negative and the sky positive.

I don't understand all this riff raff about changing the positive direction unless it significantly makes computations easier (like in Extension 2 Resisted motion problems).

I generally do -g, unless it's only going in 1 direction, so if it's a falling ball I'd use g (assuming the ball doesn't bounce up).