Re: force

[Joseph Bellina <jbellina@saintmarys.edu>]

The falling ball on spring example is a wonderful reason for developing 
the clear distinction between velocity and acceleration, since when the 
spring is fully compressed, the velocity is zero, and those who think 
velocity requires a force will argue that the net force is then zero.  I 
agree that even physicists will do this, that is how deep seated this 
notion is.  A lemma t this misconception is that zero velocity implies 
zero acceleration...hence, I think the surprise that the object has a 
zero acceleration even though it is moving.

cheers

On Wed, 30 Oct 1996, 
Roger A. Pruitt wrote:

> Here's a problem. Drop a ball on a coil spring. At what point will the
> acceleration on the ball be zero? Most students and many physicists will
> say that it is when the spring is fully compressed. WRONG! It is when
> the net force on the ball is zero. At that instant the ball is still
> moving downward and compressing the spring.
>
> I think there might be some advantage, therefore, to teaching forces
> first then kinematics. However, a better approach might be to integrate
> them more than is presently done.
>
> Roger