Earth and GravityEarth and Gravity

QuestionsQuestions

What keeps the planets in orbit What keeps the planets in orbit around the sun?around the sun?

What prevents them from flying off What prevents them from flying off into space?into space?

GravityGravity Gravity is a relatively weak Gravity is a relatively weak

attractive force that can act across attractive force that can act across great distances. great distances.

GravityGravity

Universal forceUniversal force Every object exerts an attractive Every object exerts an attractive

force on every other object in the force on every other object in the universe.universe.

Gravity and MassGravity and Mass

MassMass The amount of matter in an object.The amount of matter in an object.

Gravity is the result of mass.Gravity is the result of mass. Because all objects have mass, all Because all objects have mass, all

objects experience an attraction objects experience an attraction toward all other objects. toward all other objects.

GravityGravity

Since it is relatively a weak force……Since it is relatively a weak force……the mass of most objects is too small the mass of most objects is too small to produce a force large enough to to produce a force large enough to overcome inertia.overcome inertia.

What is inertia?????What is inertia????? The tendency for an object at rest to The tendency for an object at rest to

remain at rest or an object in motion remain at rest or an object in motion to continue moving.to continue moving.

Mass of ObjectsMass of Objects

Earth has enough mass to exert a Earth has enough mass to exert a gravitational force that can gravitational force that can overcome the inertia of objects on or overcome the inertia of objects on or near its surface.near its surface.

The larger an object is, the greater The larger an object is, the greater the gravitational force it exerts on the gravitational force it exerts on objects around it.objects around it.

Earth’s GravityEarth’s Gravity Earth’s gravitational Earth’s gravitational

force pulls everything force pulls everything toward the center of toward the center of the Earth.the Earth.

Because of this force, Because of this force, every object on every object on Earth’s surface stays Earth’s surface stays in place UNLESS an in place UNLESS an unbalanced force is unbalanced force is large enough to large enough to overcome Earth’s overcome Earth’s gravitational force. gravitational force.

How can you overcome How can you overcome Earth’s gravity?Earth’s gravity?

Lifting an object Lifting an object Jumping off the Jumping off the

groundground

Law of Universal Law of Universal GravitationGravitation

Isaac Newton Isaac Newton realized that a realized that a gravitational force gravitational force causes objects to fall causes objects to fall toward Earth and toward Earth and keeps the planets in keeps the planets in orbit. orbit.

This law summarizes This law summarizes the relationship the relationship between mass, between mass, distance, and the distance, and the force of gravity. force of gravity.

GravityGravity Gravitational attraction Gravitational attraction

increases as mass increases as mass increases.increases.

Gravitational attraction Gravitational attraction decreases as the decreases as the distance between distance between objects increase.objects increase.

Which would have Which would have greater gravitational greater gravitational attraction on Earth: attraction on Earth: Bowling Ball or Ping Bowling Ball or Ping Pong Ball?????Pong Ball?????

Weight vs MassWeight vs Mass

Mass is the measure of how much Mass is the measure of how much matter is in an object and can be matter is in an object and can be measured using a balance. measured using a balance.

Your mass is the same on Earth and Your mass is the same on Earth and on the Moon.on the Moon.

Weight is the measure of the pull of Weight is the measure of the pull of gravity on an object. gravity on an object.

Your weight would be different on Your weight would be different on Earth and on the Moon. Earth and on the Moon.

Gravity: Earth/MoonGravity: Earth/Moon

Gravity and Inertia work together to keep Gravity and Inertia work together to keep planets/moons moving in a regular orbit or path planets/moons moving in a regular orbit or path in space.in space.

The moon is in an orbit around Earth because at The moon is in an orbit around Earth because at some point it was moving past Earth. The moon some point it was moving past Earth. The moon was moving in a straight path and its inertia was moving in a straight path and its inertia was keeping it going in this path.was keeping it going in this path.

As it moved closer to Earth, Earth’s gravity As it moved closer to Earth, Earth’s gravity began to pull hard enough on the Moon to began to pull hard enough on the Moon to change the Moon’s path. change the Moon’s path.

These forces keep the moon in orbit around the These forces keep the moon in orbit around the Earth. (inertia of moon…..gravity between Earth. (inertia of moon…..gravity between Earth and Moon)Earth and Moon)

TidesTides Every day on Earth, Every day on Earth,

the water levels in the water levels in the ocean rise and the ocean rise and then drop along then drop along coastlines and coastlines and beaches. beaches.

This cycle happens This cycle happens TWICE each day.TWICE each day.

This cycle is called This cycle is called the TIDE.the TIDE.

Ocean tides are Ocean tides are caused by the force caused by the force of gravity between of gravity between Earth and the Moon. Earth and the Moon.

TidesTides The moon’s pull on The moon’s pull on

Earth causes the Earth causes the Tides.Tides.

The part of Earth that The part of Earth that is facing the Moon is is facing the Moon is pulled by the pulled by the Moon….the water on Moon….the water on Earth is pulled out in Earth is pulled out in a bulge…..HIGH TIDE.a bulge…..HIGH TIDE.

High Tide also occurs High Tide also occurs in the part opposite in the part opposite the Moon.the Moon.

TidesTides

High Tide and Low Tide occur every High Tide and Low Tide occur every 6 hours. 6 hours.

Twice each day. Twice each day.

Do all bodies of waters have Do all bodies of waters have tides?tides?

Yes……..all bodies of water (even Yes……..all bodies of water (even lakes and ponds) have tides.lakes and ponds) have tides.

However, lakes and ponds have such However, lakes and ponds have such small differences between their low small differences between their low and high tides that we do not notice and high tides that we do not notice them. them.