Don’t let it get you down!

Essential Questions

1. Define gravity

2. Explain the law of universal gravitation

AristotleAristotle

Ancient Greece around Ancient Greece around 400 BC400 BC

He believed that the He believed that the heavier the object, the heavier the object, the faster it falls.faster it falls.

Galileo GalileiGalileo Galilei

The Leaning Tower of Pisa

What is gravity?What is gravity?

Galileo

Sir Isaac Newton

Galileo helped us understand gravity as a force that exists between the Earth and objects.

Newton showed that the same force exists between all objects.

Even today, no one knows exactlywhy objects attract each other.

The size of the gravitational force The size of the gravitational force depends on two things:depends on two things:

1.1. MassMass of the objects of the objects

2.2. DistanceDistance between the objects between the objects

The Law of Universal GravitationThe Law of Universal Gravitation

What is weight?What is weight?

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

weight is expressed in weight is expressed in newtons (N)newtons (N)

Elephants & feathersElephants & feathers

Objects fall to the ground Objects fall to the ground at the same rate at the same rate because because acceleration acceleration due to gravity is the due to gravity is the same for all objects.same for all objects.

Air ResistanceAir Resistance

The amount of air resistance depends on The amount of air resistance depends on the the size size and and shapeshape of an object. of an object.

While gravity pulls an object down towards While gravity pulls an object down towards the center of the Earth, the air resistance the center of the Earth, the air resistance pushes an object up from the Earth.pushes an object up from the Earth.

Gravity &Gravity &AccelerationAcceleration

Objects accelerate Objects accelerate towards Earth at towards Earth at

9.8 m/s9.8 m/s22..

It is the same for all It is the same for all objects, objects, regardlessregardless of of their mass.their mass.

Free Fall Free Fall

When there is no air When there is no air resistance, an object is in resistance, an object is in free fall.free fall.

An object is in free fall An object is in free fall onlyonly if if gravitygravity is pulling it down is pulling it down and and no other forces are no other forces are acting on itacting on it. .