# Homework Help: Simple gravity question no math involved

1. Sep 10, 2008

### nivush1991

1. The problem statement
This is the bouncing ball lab. My question is when and why is the sign (-/+) different in the acceleration of gravity and the bouncing ball.

For example when the ball was in the air, it's acceleration was approx. 10 m/s2, which is very close numerically to the acceleration of gravity which is -9.8 m/s2. but why are the signs different. why is the acceleration of the ball positive if the accelereation of the force that's pulling the ball down (gravity) negative?

thank you

2. Sep 10, 2008

### Dick

You must be measuring distances so that larger numbers are lower than higher numbers. Flip the meter stick around.

3. Sep 10, 2008

### nivush1991

thanks a lot, definatly inspired me to write my answer.

i wrote "The signs are different between the acceleration of gravity and that of the bouncing ball because of the placement of the position detector. We placed it above the ball which would have it acting against gravity thus flipping the signs around. In order for the acceleration of gravity and the bouncing ball to be the same (both negative) we would need to place the detector on the ground beneath the ball because thatâ€™s how gravity works."

4. Sep 10, 2008

### Dick

What's important is not where the 'detector' is located. It's what direction it points. For g to be negative, larger numbers should correspond to larger elevations.