# Calculating pressure on a surface after reaching final velocity

1. Feb 6, 2012

### tegefe

I have a question. I'm conducting a drop test for packaging material and I need to find the pressure at the point of impact.
What I did was drop a 18 lb ball 18".
I converted the mass to 3.629g and the distance to 0.4572m to work in S.I. units
then used the equation 2ad=Vf^2-V0^2. Afetr doing the math I got my Vf=2.993 m/s^2, but now I have to convert that final velocity to pressure and I have no clue as to how to go about it. Can you assist?

2. Feb 7, 2012

### technician

Some things wrong with your information! an 18 lb ball is more like 9kg.
Its velocity when it hits the ground is 3m/s (not m/s^2).
To find pressure you need Force/area and to calculate the force due to an impact you need to have some idea of the time taken for the ball to come to rest.
(Force = change in momentum per second) If you do not know the time for the impact and you have no way of measuring it then you must make an educated guess!!!!
If it is a 'soft' ball it may take up to 1 second to come to rest.
If it is a 'hard' ball (like a bowling ball) it may come to rest in about 1/100 of a second.
This will give a wide range of force during impact but if your investigation is a practical exercise I hope this will be of some help.