Lunar and Planetary Institute

Gravity and Weight

In Texas, teachers are expected to teach that gravity is the force keeping planets and moons in orbit. This can be a difficult subject to teach; gravity is still not completely understood by physicists even today.  Many adults have mistaken notions as to the nature of gravity. 

5.12 D: The student is expected to identify gravity as the force that keeps planets in orbit around the Sun and the moon in orbit around the Earth

It is inappropriate to expect students at this age to understand the nature of gravity; however, they should be able to grasp the connection between gravity and mass—the Sun is massive and has a much stronger gravitational pull than the Earth has.  Mars is substantially smaller than Earth and a weaker gravity.

Preliminary Concepts
In order to understand gravity and orbits, the students must first understand that objects in motion in space will continue to move in the same direction (there is no friction in space to slow down the planets or the Moon), the planets are in orbit around the Sun, and that the planets (including Earth) are spherical rather than flat.

Activities about Gravity and Weight

Content Resources for the Pre-Service Educator

Potential Questions or Issues