1. +
Force

2. +
FORCE
 Force: is either a push or a pull that acts on an object.
 Whenever you bend, twist, stretch or compress something you are
using a pushing or pulling force.
 Force is an effect which can,
 Start motion,
 Stop motion,
 Change the speed or direction of motion,
 Change the shape or size of a body.

3. +
Unit of Force
 Force is represented by the symbol F and is measured in
Newton (N).The pull of the Earth on a 100 g mass is about 1 N.

4. +
Measuring Force
 The force is measured by a spring balance or
dynamometer.

5. +
Action and Reaction
 For every action force, there is always an equal but opposite reaction
force. If an object applies a force on a second object, then the second
object will exert an equal but opposite force on the first object.

6. +
TYPES OF FORCE
 There are many different kinds of forces:
 Gravitational force
 Magnetic force
 Electrostatic force
 Tension
 Frictional force

7. +
Gravitational Force and Weight
 Gravitational Force: The force of attraction between two
objects due to their masses
 Gravitational force depends on;
 The masses of the objects,
 The distance between them.

8. +
Gravitational Force and Weight
 Gravitational force is directly proportional to the
product of the masses: The greater the masses the
greater the gravitational force.
 Gravitational force is inversely proportional to the
distance between the masses: The larger the distance
between the objects the smaller the gravitational force.
 The pull of the earth on a 1 kg mass is about 10 N

9. +
Weight
 Weight (w): The gravitational force acting on an object. Since it is a
force it is measured by a spring scale and its unit is Newton (N).

10. +
How does weight change?
 The weight of an object on the earth depends on its
distance from the earth's centre.
 Near the earth, an object of mass 1 kg has a weight of
about 10 N, whereas 22 000 km away from the centre of
the earth, the weight of the object reduces to 1 N.
 The weight of an object of 1kg weighs most at the poles
(9.83 N) and least at the equator (9.78 N). A body having
a weight of 600 N at the equator would have a weight of
603 N at the poles

11. +
How does weight change?

12. +
How does weight change?
 The weight of an object
also changes from one
planet to another since g
is different for different
planets. However the
mass of the object is the
same in all planets.

13. +
MASS WEIGHT
It is the amount of matter It is the gravitational force
contained in substance acting on an object
It is the same everywhere It changes from place to place
It is measured by equal arm
It is measured by spring scale
balance
Its unit is kg Its unit is N
It is a scalar quantity It is a vector quantity

14. +
MAGNETIC FORCE
 Magnetic Force is the attractive or repulsive force between the
poles of two magnets.
Unlike poles attract each Like poles repel each
other (a) other (b)

15. +
ELECTROSTATIC FORCE
 Electrostatic Force is the attractive or repulsive force among
electrically charged objects or electric charges such as
electrons and protons.

16. +
TENSION
 Tension (T): It is the pulling force in a rope or a chain.

17. +
FRICTIONAL FORCE
 Frictional force: It is an important force which only acts
when two objects are touching and are applying force to
one another.
 It is a force that slows down moving objects and brings
them to rest.
 It always acts in a direction opposite to the direction of the
force applied to the object.
 Walking is possible only on a frictional surface.
 Water also applies a frictional force to the objects moving
in it.
 Frictional force does not depend on the area of the
rubbing surfaces.

18. +
 The frictional force between the object and the table
depends on two factors;
a) The weight of the object.
b) The roughness of the surfaces rubbing together.