1. Essential Question: How do mass and distance affect the gravitational pull of an object?
Standard: S8P5a. Recognize that every object exerts gravitational force on every other object and that the force exerted depends on how much mass the objects have and how far apart they are.

2. What you have learned so far…

3. Gravity
Gravity is a force of attraction between objects that is due to their masses.
All objects experience an attraction toward all other objects. This gravitational force pulls objects toward each other.
The attraction between objects will be discussed in more depth in the next essential question. For this essential question, we just need students to understand that all objects have the force of gravity pulling them toward the earth which keeps things in place unless an unbalanced force occurs.

4. Gravity
Compared with all other objects around you, Earth has a huge mass. Therefore, Earth’s gravitational force is very large.
You must apply forces to overcome Earth’s gravitational force any time you lift objects or even parts of your body.

5. Gravity
Earth’s gravitational force pulls everything toward the center of Earth.
Because of this force, the books, tables, and chairs in the room stay in place, and dropped objects fall to Earth rather than moving together toward you.

6. Unbalanced Forces Air resistance is pushing upwards
Gravity is pulling to the ground

7. What happens if you drop an elephant and a feather at the same time
What happens if you drop an elephant and a feather at the same time? Which will hit the ground first?
Why?
The force of air resistance is greater on the elephant because of its size and shape.

8. What if gravity was the only force acting on the elephant and the feather?
They would both fall at the same speed due to the earth’s gravity. This is known as freefall.

9. Remember, all objects exert a force on other objects.

10. The Law of Universal Gravitation
All objects in the universe attract each other through gravitational force.
The size of the force depends on the masses of the objects and the distance between the objects.

11. Gravitational Force Increases as Mass Increases
Imagine an elephant and a cat. Which has a larger mass?
The amount of gravity between an elephant and Earth is greater than the amount of gravity between a cat and Earth. So, a cat is much easier to pick up than an elephant.

12. Gravitational Force Increases as Mass Increases
There is also gravity between the cat and the elephant, but that force is very small because the cat’s mass and the elephant’s mass are so much smaller than Earth’s mass.

13. Watch the video clip below
Watch the video clip below. Turn to an elbow partner and discuss how the video illustrates the law of universal gravitation.
The moon has less mass than Earth does. Therefore, the moon’s gravitational force is less than Earth’s. The astronauts are not being pulled down with as much force as they would have been on Earth.

14. Gravitational force is small between objects that have small masses.
The gravitational force between objects increases as the masses of the objects increase. Arrows indicate the gravitational force between two objects.
Gravitational force is small between objects that have small masses.
Gravitational force is large when the mass of one or both objects is large.

15. The reason is that the sun is so far away.
The gravitational force between you and the Earth is large. Whenever you jump, you are pulled back down by Earth’s gravitational force.
The reason is that the sun is so far away.
On the other hand, the sun is more than 300,000 times more massive than Earth. So why doesn’t the sun’s gravitational force affect you more than Earth’s does?

16. The gravity between the sun and the planets is large because the objects have large masses. If the sun’s gravitational force did not have such an effect on the planets, the planets would not stay in orbit around the sun.

17. The gravitational force between objects decreases as the distance between the objects increases.
Gravitational force is strong when the distance between two objects is small.
If the distance between two objects increases, the gravitational force pulling them together decreases rapidly.