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.

What you have learned

so far…

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.

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.

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.

Unbalanced Forces

Gravity is pulling to the ground

Air resistance is pushing upwards

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.

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.

Remember, all objects exert a force on other objects.

The Law of Universal Gravitation

All objects in the universe attract All objects in the universe attract each other through gravitational each other through gravitational

force. force.

The size of the force depends on The size of the force depends on the masses of the objects and the the masses of the objects and the

distance between the objects.distance between the objects.

Gravitational Force Increases Gravitational Force Increases as Mass Increasesas Mass Increases

Imagine an elephant and Imagine an elephant and a cat. Which has a larger a cat. Which has a larger

mass?mass?

The amount of gravity between an elephant The amount of gravity between an elephant and Earth is greater than the amount of and Earth is greater than the amount of

gravity between a cat and Earth. So, a cat gravity between a cat and Earth. So, a cat is much easier to pick up than an elephant.is much easier to pick up than an elephant.

Gravitational Force Increases Gravitational Force Increases as Mass Increasesas Mass Increases

There is also gravity between the cat and the There is also gravity between the cat and the elephant, but that force is very small because elephant, but that force is very small because the cat’s mass and the elephant’s mass are so the cat’s mass and the elephant’s mass are so

much smaller than Earth’s mass.much smaller than Earth’s mass.

Watch the video clip below. Turn to an Watch the video clip below. Turn to an elbow partner and discuss how the video elbow partner and discuss how the video illustrates the law of universal gravitation.illustrates the law of universal gravitation.

The moon has less mass than Earth The moon has less mass than Earth does. Therefore, the moon’s gravitational does. Therefore, the moon’s gravitational force is less than Earth’s. The astronauts force is less than Earth’s. The astronauts are not being pulled down with as much are not being pulled down with as much force as they would have been on Earth.force as they would have been on Earth.

https://www.youtube.com/watch?v=3Cm83yYtDns

The gravitational force between objects The gravitational force between objects increases as the masses of the objects increases as the masses of the objects

increase. Arrows indicate the increase. Arrows indicate the gravitational force between two objectsgravitational 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.

The gravitational force between you and the Earth is large. Whenever you jump,

you are pulled back down by Earth’s gravitational force.

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?

The reason is that the sun is so far away.

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.

The gravitational force between objects The gravitational force between objects decreases as the distance between the decreases as the distance between the

objects increases.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.

StudyJams: Gravity & Inertia