# Force and Acceleration

1. Sep 7, 2010

### GreenLRan

In class today, my professor said that you will never find a force that is a function of acceleration.

Why is this?

M$$\ddot{x}$$(t) = F(x,y,z,$$\dot{x},\dot{y},\dot{z}$$,t)
M$$\ddot{y}$$(t) = F(x,y,z,$$\dot{x},\dot{y},\dot{z}$$,t)
M$$\ddot{z}$$(t) = F(x,y,z,$$\dot{x},\dot{y},\dot{z}$$,t)

This is in a classical mechanics / dynamics course

2. Sep 9, 2010

### rock.freak667

Usually forces vary with time, because acceleration would vary with time. I think he meant that you would not find a function such that F=2a2+a+3 as that would not work dimensionally.

3. Sep 9, 2010

### rcgldr

What about a reaction force? For example a string attached to a ball and accelerating the ball, the force the ball exerts on the string is a function of the acceleration of the ball.

4. Sep 9, 2010

### rock.freak667

Well that is what I am saying, I think your professor meant that you would not usually measure force with acceleration or well plot force against acceleration.