Why do physicists say mass is more fundamental than weight? ?

because mass of a matter never changes

on the other hand the weight of a matter changes due to gravity

for example the

on the moon the pull of gravity is less than it is on earth so the Weight of an object will be less on the moon but the mass of it will stay the same

Explanation:

I

the body's situation won't change the forces are equal opposit and on the same body

answer; equivalent to a one(1) horsepower motor;