GravityGravity

GravityGravity

A force of attraction between objects that A force of attraction between objects that is due to their masses. is due to their masses.

Because gravity is less on the moon

than on Earth, walking on the moon’s surface

was a very bouncy experience for the Apollo astronauts.

All Matter Is Affected by GravityAll Matter Is Affected by Gravity

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

Because of gravity you Because of gravity you are being pulled toward are being pulled toward this book, your pencil, this book, your pencil, and every other object and every other object around you. Do you around you. Do you know why?know why?

Earth’s Gravitational Force Is LargeEarth’s Gravitational Force Is Large“It’s Truly Incomparable”“It’s Truly Incomparable”

Compared with “all” the objects around you, Compared with “all” the objects around you, Earth has a enormous mass.Earth has a enormous mass.

The Law of Universal GravitationThe Law of Universal GravitationDiscovered by Newton in Discovered by Newton in

the late 1600’s while he the late 1600’s while he watched an apple fall from watched an apple fall from a treea tree

He said that the force that He said that the force that pulled the apple to the pulled the apple to the ground was the same force ground was the same force that keeps the moon and that keeps the moon and earth in it’s orbit earth in it’s orbit

Universal Gravitation: Universal Gravitation: Two bodies attract each Two bodies attract each other with equal and other with equal and opposite forcesopposite forces

The magnitude of this The magnitude of this force is proportional to force is proportional to the product of the two the product of the two masses and is also masses and is also proportional to the proportional to the inverse square of the two inverse square of the two bodies.bodies.

                ,

The Law of Universal GravitationThe Law of Universal Gravitation

The Law of Universal Gravitation states that all objects The Law of Universal Gravitation states that all objects in the universe attract each other through gravitational in the universe attract each other through gravitational force. The size of the force depends on the masses of force. The size of the force depends on the masses of

the object and the distance between them.the object and the distance between them.

http://phet.colorado.edu/en/simulation/gravity-force-lab

For Example…For Example…

Gravitational force increases as Gravitational force increases as mass increases. mass increases.

Imagine an Elephant and a CatImagine an Elephant and a CatOr imagine the Earth and the MoonOr imagine the Earth and the Moon

Gravitational force decreases as distance Gravitational force decreases as distance increases.increases.Gravity between you and the EarthGravity between you and the EarthGravity between you and the SunGravity between you and the Sun

Weight and Mass are DifferentWeight and Mass are Different

Weight is a measure of the gravitational Weight is a measure of the gravitational force exerted on an object.force exerted on an object.

Do you know what that means?Do you know what that means? Mass is the amount of matter “Stuff” in Mass is the amount of matter “Stuff” in

an object, and its value does not an object, and its value does not change.change.

Free FallFree Fall

Occurs when the only force acting on an Occurs when the only force acting on an object is gravityobject is gravity

All objects in free fall accelerate at the same All objects in free fall accelerate at the same raterate

W = mgW = mgg = 9.8 m/sg = 9.8 m/s22

Derived from Newton’s Derived from Newton’s 22ndnd law: F=ma law: F=ma

Acceleration are due to GravityAcceleration are due to Gravity

Acceleration due to gravity = g = 9.8 m/s2

Falling ObjectsFalling Objects

MisconceptionsMisconceptions Astronauts are not experiencing Astronauts are not experiencing

weightlessness. They are in weightlessness. They are in free fall along with all the other free fall along with all the other objects around them. Since objects around them. Since they are all “falling” at the same they are all “falling” at the same raterate

Without air resistance, all Without air resistance, all objects will drop at equal ratesobjects will drop at equal rates

Skydivers are not in “free fall” Skydivers are not in “free fall” because air resistance is also because air resistance is also acting on them.acting on them.

Projectile MotionProjectile MotionHas 2 componentsHas 2 componentsConsists of vertical Consists of vertical

and horizontal and horizontal velocitiesvelocitiesHorizontal = launchHorizontal = launchVertical = gravityVertical = gravity

Causes a curved pathCauses a curved pathThis is why you should This is why you should

always aim a targetalways aim a target

Orbital MotionOrbital Motion

http://phet.colorado.edu/en/simulation/gravity-and-orbits

For Review…For Review…How does the mass of an object relate to How does the mass of an object relate to

the gravitational force the object exerts on the gravitational force the object exerts on other objects?other objects?

How does the distance between objects How does the distance between objects affect the gravity between them?affect the gravity between them?

Comparing Concepts: Explain why your Comparing Concepts: Explain why your weight would change if you orbited Earth weight would change if you orbited Earth in the space shuttle but your mass would in the space shuttle but your mass would not?not?