National Science Education Standards:

Content Standard A: Science As Inquiry
Content Standard D: Earth and Space Science – Properties of Earth materials

This activity helps students experiment with gravity to see how gravity works.

(BACKGROUND INFORMATION)
This is what we already know about gravity:

• Gravity is one of the fundamental forces of nature.
• Gravity is a force that pulls objects toward each other.
• The mass of an object and distance between objects affects the strength of the force of gravity. Greater masses attract with more force and the force weakens as the objects get further apart.
• Earth’s gravity pulls objects toward the Earth’s center.
• The force of gravity works with an object’s mass to determine the weight of that object.

Activity - Gravity at Work

one 1-gallon milk container, 30 marbles, rubber band, scissors

Pre-Lesson Instructions:

1. You may choose to run this activity as a whole-group activity or in smaller groups.
2. Cut rubber bands, and attach one securely to the handle of each milk container
3. Review the concept of gravity by watching the “What is gravity?” video newsbreak.

1. Distribute materials and explain to students that they will do an experiment to show gravity at work.
2. Have groups place about one-half of the free end of the rubber band on a desk so that the container dangles over the side.
3. Ask one child to hold the rubber band in place to support the container.
4. Have students place marbles in the container in groups of five. Explain that gravity pulls the container toward Earth, making the rubber band stretch. Tell students that as the milk container becomes heavier, the stretch of the rubber band is a measure of the gravitational force.
5. Now, let groups choose a different child to hold the rubber band, and have students explore subtraction by taking groups of five marbles out of the container. Continue until the container is empty.
   
6. Discuss what happens to the container and rubber band as marbles are added to the milk container. Tell the students that as more mass is added to the container, the gravitational pull increases. That is defined as weight. The more mass an object has, the more it weighs on Earth.
7. Discuss what happens to the container and rubber band as marbles are removed. Tell students that the mass has been lessened, therefore, the weight is less. The gravitational pull has decreased.

Extension:

Since weight is affected by a planet's gravitational pull, how would this activity be different if we completed the activity on the moon. The moon has about 1/6 Earth's gravitational pull.