Question about acceleration

[Deepak Kapur]

I push a ball hard. It starts to move.

 

 

1. Does it accelerate only for the time 'from my hand touching it' to 'my hand leaving it'?

 

2. After my hand leaves the ball, it attains uniform motion ( assuming no kind of friction). What sustains this uniform motion?

 

3. Why does the ball ever move? Why doesn't the energy that I supply to it just gets distributed as its internal energy?

[imatfaal]

I push a ball hard. It starts to move.

 

 

1. Does it accelerate only for the time 'from my hand touching it' to 'my hand leaving it'?

 

2. After my hand leaves the ball, it attains uniform motion ( assuming no kind of friction). What sustains this uniform motion?

 

3. Why does the ball ever move? Why doesn't the energy that I supply to it just gets distributed as its internal energy?

 

1. Yes. When there is no external force from your hand or other sources it does not accelerate.

 

2. Nothing sustains it - this goes back to Galileo and Newton; uniform motion at a constant velocity is the ground state which requires no sustenance or input, only changes to this uniform velocity require an external force. This is a basic rule of the way the universe works.

 

3. Force is momentum change. You apply a force without a countering force and you will have resultant net force - the net force will cause a change in momentum - an acceleration.

[studiot]

Just to be crystal clear.

 

Velocity is a vector quantity. This is it has both speed and direction.

 

Change either and it is an acceleration.

 

Acceleration is also a vector quantity, with magnitude and direction.

 

It take energy to change the speed but no energy to change the direction.

But in both cases a force has to be applied to cause this.

 

Can you see why?

Can you see the connection to the definition of work?

Edited June 2, 2014 by studiot

[Deepak Kapur]

 

 

It take energy to change the speed but no energy to change the direction.

But in both cases a force has to be applied to cause this.

 

 

A ball is moving. I hit it with another very small ball at an angle so that its direction changes.

 

Isn't it the 'energy' of the small ball that has brought this change in direction?