Final answer:
Momentum is indeed the product of mass and velocity, and objects with more mass have more momentum, assuming velocity is constant. The difference in breaking a glass on cement versus grass can be explained by impulse, which is the force multiplied by the time over which it is applied; cement provides a higher impulse due to a rapid stop.
Step-by-step explanation:
I agree with your friend's claim that momentum is mass multiplied by velocity. In physics, momentum (p) is defined as the product of an object's mass (m) and its velocity (v), with the formula being p = m × v. This means that for any given velocity, a more massive object will indeed have more momentum. It's also important to note that since velocity is a vector, momentum is also a vector and has direction.
Regarding the glass dropping on different surfaces, when the glass hits the cement floor, it comes to a stop much more rapidly than it would on a grass lawn. The force involved and the short time interval during which that force acts result in a greater impulse, which is the force multiplied by time (J = F × Δt), on the cement floor. A greater impulse on the cement means a more abrupt change in momentum, which is more likely to break the glass.