ShareForce, Energy, & Motion - The Gravity Way!
To understand the forces of gravity you need to know the difference between mass and weight. How much do you weigh? How much mass do you have? (If you don't know, you can calculate your mass! Divide your weight in pounds by 2.2, this is how many kilograms you have which is your mass.)
Gravity is the attractive force between all objects in the universe. It is the force that pulls objects to Earth.
Galileo, a famous Italian scientist who lived in the 1500s, was the first to discover the force of gravity. In his famous experiment he dropped two cannonballs, one 10 times the mass of the other, at exactly the same time from the Leaning Tower of Pisa. Which cannonball do you think hit first? Before you answer the question set up your own experiment.
Materials:- Two similar size objects that have different masses
- Another observer
- While standing on the floor, drop both objects at the same time, from the same height.
- Now stand on a chair and again drop both objects at the same time, from the same height.
- Find something that is still taller that you are allowed
to stand on.
- Now drop both objects again - at the same time and from the same height.
Safety concerns: 
Be sure to follow all eye safety rules that are specified by your teacher in all general laboratory
experiences. As with all science lab activities, the most important safety
rule is to follow all teacher directions.
- Was there a difference in which object hit the floor first?
- Did the height you stood above the ground change the order in which the objects landed?
- How did the time required for the objects to hit the ground change as you increased the distance they were above Earth?
Remember that mass is measured in the metric system in kilograms. Mass is the amount of matter in an object. For example, while an astronaut in space is weightless, he still has mass! Which has more mass, real car or a toy car?
Weight on the other hand is not the same thing as mass. The force of gravity pulling at the object or the object's mass is called weight.
Recall that gravity is the attraction between two masses. All objects that have mass also have a gravitational force. The larger the mass the more gravitational pull the object has. Even a tiny dust particle has gravity. Do you have gravity? Of course you do - but compared to Earth, your gravity does not affect many things around you. So now, which has more gravity, you or Earth?
As you may have discovered in the activity, distance can have an affect on gravity. Thinking about this, if you were a astronaut, and you go farther into space, why do you become weightless? Well, as your distance from Earth increases, the force of gravity between you and Earth decreases. So when you're in space, gravity has less effect on your mass. Look closely at the following diagram to help you understand this concept.
