# page79 PhySP18SS5.3.29 The best way to describe the subtle differences between inertial mass and gravitational mass is the weird fact that objects with different masses still fall to the earth with the same acceleration (g=9.81m/s/s). Why is this? It’s cray cray. Gravitational mass goes into the weight formula (weight=mg) It is the force that causes the object to accelerate towards the earth. So the basketball dropping from the stadium experiences TEN TIMES the force from the earth to fall to the earth than a tennis ball that is falling beside it. So why doesn’t it fall 10x faster than the tennis ball. They hit at the same time with the same speed. WHAT? It’s because the basketball has TEN TIMES the RESISTANCE to fall (as represented by its inertial mass). So there is a perfect balance of attraction of the two balls to the earth and resistance of the two balls to be pulled to the earth. The tennis ball doesn’t have a lot of weight (mg) so not much of an attractive force, but it only has 1/10 the resistance to the pull of the earth. So they are attracted at the same 9.81m/s/s or 32.2ft/s/s. Wow, this is the longest caption I have ever wrote.