Re: If i dropped a pole in sand would it go in as far on the moon?

Hi Tom,

Be careful of confusing weight and mass. Traditionally, "weight" really means "the force of gravity." It depends upon two things--the mass of the object whose weight you're talking about, and the mass of the planet upon which you're standing. Mass, on the other hand, is just the total amount of matter in an object, and is completely independent of where that object is located.

When you drop a pole into sand, it will first be accelerated downward by the force of gravity. This is weaker on the Moon than on Earth, and so the pole will accelerate more slowly on the Moon. When the pole strikes the sand, it will penetrate to some depth. The depth depends upon the inertia of the sand (its mass), which causes it to resist being pushed aside. It also depends upon how much energy the pole has to push the sand aside which in turn is determined by how quickly it is moving (faster=more energy). As compared to the situation on Earth, the pole is moving more slowly when it hits the sand on the Moon, and so has less energy. On the other hand, the mass of the sand is the same, and so the pole has to expend the same amount of energy to penetrate to a given depth. As a result, the pole will penetrate a lesser distance into the sand on the Moon.