# 4F Gravitational Attraction

### IPC2 Kennison

Objectives

· Describe gravity as a force that exists between any two objects that have mass"

· Demonstrate that all objects, regardless of their mass, fall to the ground at the same rate"

Overview

We often take the force of gravity for granted, even though Earth's gravity is what keeps each of us from floating off into space! In this lesson, you will begin to more fully understand and appreciate the force of gravity. They predict what will happen when a whole apple and half an apple are dropped at the same time from the same height then test their predictions. Next, they observe cannonballs of different masses being dropped out of a tower, and leaking cups being dropped into a bucket. These activities demonstrate that all objects fall at the same rate, regardless of their mass - a concept known as the law of falling bodies. Students then watch a video segment showing a NASA astronaut dropping a feather and a hammer on the Moon. They repeat the activity in the classroom then consider why these objects fall at the same rate on the Moon but not on Earth. Finally, they use what they have just learned to predict what will happen when two balls of the same mass but different volumes - and then two balls of different masses but the same volume -- are dropped at the same time from the same height.

Before you begin, you may want to review the following terms. Mass is the amount of matter in a given volume of something. Volume is the amount of space that an object or substance takes up. For example, the mass of a bag of fluffy marshmallows is the same before -- and after -- a stampede of elephants changes its volume by squishing it to the size of a bar of soap. An object's mass is what determines how much force is needed to move, speed up, or slow down the object. The greater the object's mass, the more force it takes to change its motion.

Gravity is the force that exists between any two objects that have mass. Weight is a measure of the force of gravity pulling on an object. Some people think that the mass of an object and its weight are one and the same, probably because we weigh things to determine their mass. But weight and mass are not the same. How much something weighs depends on how strongly gravity is pulling on it. So something will weigh less where the gravitational force on it is weaker (as on the Moon or in space, for example), even though its mass has not changed.

Now go to this virtual lab to explore and describe the gravitational attraction between objects of different masses at different distances.