Lunar and Planetary Institute






Gravity and Weight
Potential Questions or Issues

Some students may want to understand why the planets don’t fall into the Sun; they will need to understand that friction is what causes most items on Earth to slow down and fall to the ground. 

Students may also become sidetracked into discussions of black holes.

Students might be concerned that their weight on Mercury and Mars are the same, or that their weight at Saturn is not much more than on Earth—you may have to discuss density, and that standing on the surface of a dense planet will increase your weight, while being outside of a very non-dense planet will decrease your weight.