🚀 go-pugleaf

My senior physics class had some questions that I need help with.
(You may want to reply to these separately?)

1. What is the difference between centre of mass and centre of gravity?
   (preferrably withexamples of the difference if there is one).

2. The formula for calculating %error is
        (measured value - accepted value)/ accepted value    x100%
   They had to calculate the total torque on a mobile (made of wooden blocks
   and fishing line). The total torque on each block should be zero for
   it to be in equilibrium, BUT how do you calculate the %error when the
   accepted value is zero?

3. What exactly happens to plastic that turns it white when you make a
   sharp bend in it. (this is probably chemistry).

Thanks.

Michael Harwood.     harwood@quark.physics.uwo.ca
(Physics Teacher, Ingersoll District Collegiate Institute, Ingersoll, Ontario)