Gravity

S: Gravity and Acceleration

April 8, 2008

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.

In the late 1500s, an In the late 1500s, an Italian scientist named Italian scientist named GalileoGalileo Galilei decided Galilei decided to prove Aristotle wrong.to prove Aristotle wrong.

Galileo theorized that all Galileo theorized that all objects will land at the objects will land at the same time when they same time when they are dropped from the are dropped from the same heightsame height..

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.

What is gravity?What is gravity?

Galileo

Sir Isaac Newton

Galileo and Newton 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.

It all starts with an apple…It all starts with an apple…

Isaac NewtonIsaac Newton 1655 1655

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.

Since gravity is a force and weight is a Since gravity is a force and weight is a measure of gravity, weight is expressed measure of gravity, weight is expressed in in newtons (N).newtons (N).

Gravity &Gravity &AccelerationAcceleration

The rate at which The rate at which objects accelerate objects accelerate towards Earth is towards Earth is 9.8 9.8 m/sm/s22..

This acceleration is the This acceleration is the same for all objects, same for all objects, regardless of their regardless of their mass.mass.

Air ResistanceAir Resistance

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

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

Free FallFree 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 only if An object is in free fall only if gravity is pulling it down and gravity is pulling it down and no other forces are acting on no other forces are acting on it. it.

Terminal VelocityTerminal Velocity

Force of gravity = air resistanceForce of gravity = air resistance

This is the highest velocity reached by a This is the highest velocity reached by a falling object thus it has 0 acceleration falling object thus it has 0 acceleration and falls with constant velocity.and falls with constant velocity.