Force can push or pull objects and cause them to move, stop, change speed or direction. Gravity and friction are two main types of forces. Gravity pulls objects toward the center of Earth while friction resists the motion of objects. Simple machines like levers, pulleys, inclined planes and wheels make work easier by reducing the amount of force needed. Different forms of energy include light, heat, sound, electrical and various natural resources like solar, wind and hydro energy which are used to power homes and generate electricity.

1. Force, Work and Energy
Class 4 Science

2. Force

3. What is force ?
• A force is a push or a pull on an object
that is caused by an interaction with
another object.

4. Effects of force
• A force can move a stationary object.
• A force can slow down or stop a moving
object.
• A force can change the speed of a moving
object.
• A force can change the direction of a moving
object.
• A force can change the shape and size of an
object.

5. Types of force
• Gravitational Force : Gravitational force or
gravity is the force that attracts objects to the
centre of the Earth.

6. GRAVITY
Example
When a ball is thrown in the air, it comes back
towards the earth due to gravitational force, an
apple falling from a tree, etc.
• Force off gravity is acting on an object even
when the object is at rest.

7. Types of force
Frictional force or friction : Frictional force
or friction is the force that tries to stop
the movement of objects across a
surface. Friction always acts in the
direction opposite to the direction of
movement of an object.

8. FRICTION
• The force that is present when two things
are in contact with each other is called a
friction.
• This force resist the motion of an object on
the surface. As a result ,the object either
slows down or stops moving.
• Materials with a smooth surface (Eg. glass or
ice) causes less friction than materials little

11. Recap time
1) The force that pulls objects toward the center of the
Earth is called:
a. a push or pull
b. friction
c. mass
d. gravity
2) Something that makes objects start moving, stop
moving, slow down or change direction is a:
a. a push or pull
b. friction
c. mass
d. gravity

12. Recap time
3) Which of the following surfaces has the least amount of
friction?
a. a gravel driveway
b. a dirt road
c. a road covered with ice
d. a road covered with spilled sand
4) Megan throws a paper airplane. How will gravity
make the airplane move?
A.in a straight line
B.up toward the sky
C. back toward Megan
d. down toward the ground

13. WORK
• Work is said to be done
only when the force
applied an object cause it
to move through a
distance or a change in
the shape or size of that
object.
• Eg: The football moves,
when a child kick it .

14. Simple machines
Machines are simple tools which make
our work easier and faster with use of
less energy. They help us to do many
works.

15. Types of simple machines
There are 6 types of simple machines:-
• Lever
• Pulley
• Inclined plane
• Wheel and axle
• Screw
• Wedge

16. 1. Lever
•A lever is a simple
machine that is made up
of rod resting at a point
around which it moves.
•It is used to lift or move
heavier weights, cut
things or open the lid of
a tin.
•Eg: a pair of scissors ,
see-saw, bottle openers,
paper cutter etc.

17. Pulley
• A simple pulley is a
wheel with a groove
along its edge, for
holding a rope or a chain.
• It is used to lift heavy
objects attached to one
end of the rope
• Eg- Pulley is used to pull
water from a well.

18. Wheel and Axle
• Wheel and axle is a
simple machine.
• It is used to move a
heavy load using less
effort.
• It consists of a wheel
rigidly attached to a
rod (called axle).
When one rotates the
wheel, the axle also
rotates.

19. Inclined Plane
• An inclined plane is a sloping
surface daddy issues are to push or
pull heavy objects to a certain
height .
• It makes it easier to lift a heavy
object.
• It is easier to pull or roll an object
up an inclined plane than to lift it
directly.
• Eg- A sloping plank is used while
loading barrels into a truck.
• Inclined plane is used in hospitals
to push up the wheelchair.

20. SCREW
Types of Inclined Plane
• 2. WEDGE

21. Types of Inclined Plane
1. SCREW
• A screw is actually an
inclined plane wrapped
around a cylinder that has
a sharp pointed end.
• Screw helps to attach
things to each other.
• Screws are turned with
the help of a screwdriver.
As they rotate they also
move forward.
2.WEDGE
A wedge has at least one
incline plane ending in a
sharp edge.
This sharp edge helps to
cut things.

22. Energy and its
Resources

23. Energy

24. What is Energy ?
• The ability to do work is called energy.
• There are many forms of energy

25. Types of energy
• Heat energy
• light energy
• solar energy
• Wind energy
• Hydroenergy
• sound energy
• geothermal energy
• mechanical energy
• electrical energy

26. Forms of energy
• Heat energy: Burning fuels such as coal, LPG, and
kerosene release heat energy. In our homes, we
use heat energy to cook food.

27. Forms of energy
• Light energy: Light energy helps us to see things
around us. Electric bulb, lamp, tube light, and
candle are some sources of light energy.The sun is
also a source of light energy.

28. Forms of energy
• Solar energy: The energy that we get from the sun is called solar
energy. It is used to provide heat, light, hot water, and
electricity.

29. Forms of energy
• Wind energy: Power of the moving air (wind) is utilized with the
help of windmills to generate electrical energy.

30. Hydro energy
•Moving water also has a lot of
energy in it. this energy is called
hydro energy. to use this energy,
we build dams. these dams
allow the water to fall from a
height onto turbines with great
force. then turbines move and
helps to produce electric energy.

31. Forms of energy
• Sound energy: Portable audio players, television, radio, and
loudspeakers are sources of sound energy. Musical
instruments such as guitar and tabla also produce sound
energy.