What does density have to do with it?
And I'm not sure you could find a PVC pipe that is thin enough to weigh the same as a wiffleball bat, and if you did, it would have the same properties as the wiffle bat, I would think.
What do you think mass applies to? Although a ton of feathers and a ton of lead weigh the same, drop them and the gravitational pull on the feathers is less because of the difference in density.
Newton's law deal with the change of momentum, thus f=ma.
