Gravity

What is acceleration?What is mass?What is force?

When the ball is release, the ball will reach the ground. Why?

2.8 Understanding

Gravity

Explain and determine the value of acceleration due to gravity

Define gravitational field and gravitational strengthDefine weightSolve problems involving acceleration due to gravity

To study the relationship between acceleration of an object and mass

Material : Water bottle (2)

Conclusion

Both objects reach the bottom at the same timeBoth objects reach the bottom at the same time

The acceleration of an objects does not depend on the massThe acceleration of an objects does not depend on the mass

Definition: Acceleration of an object due to the pull of the gravitational force only.

The value of acceleration due to gravity, g is 9.8 ms-2

An object is falls freely under the influence of gravitational force only

Definition: Region in which an object experiences a force due to gravitational attraction

Any massive object that enters this field will experience a force of attraction

This field will get weaker the further you go out from the centre of earth

Earth: half sizeEarth: half size

Earth: Half Size

GRAVITATIONAL FIELD

Gravitational field strength is defined as the gravitational force per unit mass

Gravitational field strength of the earth is 9.8 N kg-1

Gravitational field strength of moon is 1.6 N kg-1

m

Fg

1 Nkgkg

N

A ball falls vertically a distance of 125 m to the ground. Using g = 9.8 ms-2 ; calculate:

a)Time the ball takes to fall the first 25m

b)Time the ball takes to reach the ground

c)The velocity of ball before it hits the ground

Define: Gravitational force acting on a body

Where mass is m and g is gravitational field strength or the acceleration due to gravity

Unit = N

mgW

What is Ali’s weight on the earth and moon if its mass is 70kg?Use g earth = 9.8 ms-2 and g moon = 1.6 ms-2

Question time…

1 23 4

Question 1Our bodies are pulled down to the earth's surface by

A.Newton’sB.WeightC.Gravity

Question 2Object with different mass have ……… acceleration due to gravity

A.DifferenceB.SameC.Zero

Question 3Value of acceleration due to gravity on earth is 9.8 ms-1

A.TrueB.False

Question 4If an object fall with an acceleration due to gravity, the velocity of the object must……

A.Be constantB.Continuously change by the same amount each second

C.Continuously change by varying amount each second

D.Continuously decrease

Acceleration due to gravity is the acceleration of an object due to the pull of the gravitational force

Gravitational field is the region in which an object experiences a force due to gravitational attraction

Free fall is an object falls under the influence of gravitational force only

Gravitational field strength is the gravitational force per unit mass

Weight is the gravitational force acting on a body