Gravity

Gravity is a pulling force

It pulls things down towards the earth

Things fall because of gravity

Things always fall down

Gravity was discovered by a scientist called Isaac

Newton

Stories say he discovered Gravity when an apple fell

on his head

What is gravity?

Gravity is the force of attraction between any two objects.

Gravity holds everything and every one on the earth

Even in Australia

In Space, Gravity keeps the planets moving around the

sun

Gravity depends on:

1- Mass of an object

2- distance between objects

Earth’s gravitational acceleration

Try to drop a science book and a paper at the same time, which would hit the ground first????????? (suppose there is no air resistance)

Free falling object would fall with the same acceleration.

Acceleration of gravity is 9.8m/s2

According to Newton’s second law:

Fnet= m x a

What is the force of gravity exerted on an object??

F = m x acceleration of gravity

F= m x g

Application

• What is the gravitational force on an object with a mass of 60 Kg?

• Find the force exerted by a rope on a

10 Kg mass that is hanging from the rope.

Weight

• Does gravity exert a force on you while you are sitting know thinking to find an answer for this question?

• The gravitational force exerted on an object is called weight.

• Because the weight of an object is equal to the Earth’s gravity on the object, weight can be calculated from this equation:

• W = m x g

Application

• On Earth, what is the weight of a large-screen TV that has a mass of 75 Kg

• Find the acceleration of gravity on Mars if a person with a mass of 60 Kg weighs 222N on Mars.

MASS Mass is a physical property of matter that

explains how much matter is in an object

Mass does not change when gravity changes

WEIGHT Weight is a force which is

calculated by multiplying the acceleration of

gravity times mass. Weight can change when

gravity changes

Mass and Weight are two different Properties of Matter

• An elephant on the Earth would weigh less on the Moon, because gravity is less on the moon.

• An elephant’s mass would not change if he went to the moon

WEIGHT