# The Sun Wants Us Closer Lab - Sun's Gravitational Pull

## The Sun Wants Us Closer Lab - The Sun's Gravitational Pull

In everyday language, gravity is defined as the force that pulls everything down toward the surface of the Earth. It proves the old saying that “what goes up, must come down.” It can be felt and experienced on a daily basis. For instance, people are able to walk on the ground easily and without floating due to gravity. Leaves fall from the trees and nothing stays afloat due to gravity. Gravity is also observed in the Solar System, which contains other planets like Earth, and are all orbiting around the Sun in elliptical paths.

To illustrate this, imagine cutting a rubber band, tying a ball to one end, and twirling it around as shown in the image below. The tension in the rubber band makes the ball move in circle, but if you cut the rubber band, there is no more force to keep the ball moving in circle. Thus, the ball will fly off in a straight line. If you stop twirling the ball, the rubber band will pull back in toward your hand. This scenario is similar to how the planets move around the Sun. If there was no gravitational force between the planets and Sun, the planets will just fly off into space. If the planets do not have sideways motion, they would be pulled into the Sun by the gravitational force.

The motion of a twirling ball attached to a rubber band (A) is similar to the motion of the planets in our Solar System around the Sun (B).

In this laboratory activity, you will make a model for gravity and our Solar System using pool balls, marbles, and a sheet of stretchy fabric. Through this activity, you will learn how gravity dictates the movement of celestial objects in the Solar System.

### Sun's Gravitational Pull Learning Objective:

At the end of this laboratory activity, students are expected to:

• Make a model for gravity and our Solar System using pool balls, marbles, and a sheet of stretchy fabric.
• Use the model for gravity in explaining the movements of celestial objects in the Solar System.

### Laboratory Proper:

Materials:

• Large sheet of stretchy fabric (ex. polyester / spandex / Lycra), approximately 2 yards by 2 yards
• Marble set that includes larger “shooter” marbles in addition to regular marbles
• At least one billiard ball (Alternatively, you can use heavy round fruits like oranges, melon, or grapefruit)
• 8 to 10 chairs (identical in height and has backrest)
• Plenty of document clamps or metal clothes pin

Procedure:

1. Form a group of 8 for this activity.
2. Arrange 8 to 10 chairs in a circle.
3. Stretch the sheet of fabric over the backs of the chairs. Secure the fabric using the clamps or clothespins.
4. Adjust the tightness of the sheet by moving the chairs farther apart or closer together as needed. Try to avoid wrinkles or dips in the fabric.
5. Put the billiard ball in the middle of the fabric sheet. Make sure it sags down in the middle.
6. Let each member get one marble and place each on the edge of the fabric. Release the marbles one at a time. Observe what happens.
7. Get another marble and put it closer the middle of the fabric sheet, instead of at the edge, and release them. Observe what happens.
8. Get another marble and try rolling it towards yourself (away from the billiard ball) and then let go. Observe what happens.
9. Remove the billiard ball from the middle of the sheet and make sure that the sheet is stretched

10. Ask two members of the group to put one marble on the opposite sides of sheet, near the edge of the fabric. Observe what happens.
11. Put back the billiard ball in the middle of the fabric sheet.
12. Let each member get marbles of different sizes and place each on the edge of the fabric. Release the marbles at the same time. Observe what happens.

## The Sun Wants Us Closer Lab - Gravitational Pull Activity:

Students record their predictions and results of the lab activity. Once the activity is finished, discuss the lab activity and answer post-lab questions.

We also provided some of the Resources below for you to use in class. iTeachly Members can access all the content for the activity and the following lesson.

Students must come up with a unanimous answer for each question. Discussing the answers usually, results in some excellent dialogue on this topic.

## The Sun Worksheets - Word Docs & PowerPoints

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