# Sign of Acceleration of dropped tennis ball at the floor

## Homework Statement

You drop a tennis ball on a hard floor, and it bounces upward. If the x-axis is directed upward, what is the sign of the acceleration while the ball is in contact with the floor?

a=v/t

## The Attempt at a Solution

I thought that the acceleration when the ball hits the floor would be 0 because the ball's speed is 0 at that point in time, and because there was no acceleration at that point then there would be no sign for it. The correct answer is that the acceleration is positive. As a side note, I believe the ball does not have a direction when it is in contact with the ground (please correct me if I'm wrong).

A ball can have 0 speed and a non-zero acceleration. In fact, it has to in order to go from a stopped position (floor) to a velocity that is not zero(upward)

A ball can have 0 speed and a non-zero acceleration. In fact, it has to in order to go from a stopped position (floor) to a velocity that is not zero(upward)
Okay, that makes sense. Thanks a lot!

CWatters
Homework Helper
Gold Member
And it does have a direction.

haruspex
Homework Helper
Gold Member
There is a small flaw in the question. From the instant the ball touches the floor, the acceleration will continue to be downwards until the point at which the compressive force in the ball matches the ball's weight. Similarly, after rebounding to the same point, the acceleration will again be downwards.

Vibhor and CWatters
James R