Gravity is an example of friction. If we didn't have gravity, we would be flying all over the place. Also, friction keeps us from sliding on the ground and falling.
Answer:
No external contact force.
Explanation:
Mass is defined as the amount of material an object contains, that doesn't change whether the object it on earth, on the moon or anywhere in space. Except the only force that is acting upon the body in gravity and they don't feel gravitational attraction towards the earth.
The answer a boulder has more mass and stuff like that.
In several of the questions you've posted during the past day, we've already said that a wave with larger amplitude carries more energy. That idea is easy to apply to this question.
