A because it some type of friction
The 2nd Law says F=ma, where F is the force in Newtons, m is mass and a is acceleration. Earth's gravity is an acceleration, 9.8m/s^2. So you can solve the equation for mass, m=F/a, or m=F/9.8 where you've measured the force (weight) in Newtons.
Refraction is the change in direction of a wave.
Diffraction is the bending of a wave around a barrier.
