For class 7 science

1. UNIT 2 15/3/2016
LESSON 1

2. FORCE
 It is an effect attempts to change the object’s phase
from being static to motion or vice versa or attempts
to change the direction of motion.

3. Universal Forces in Nature
Lightening Thunder
The attraction of
object to Earth
Wind motion
The attraction of
iron to magnet

4. Universal Forces in Nature
Attraction forces
Electro magnetic forces
Nuclear forces

5. 1. Attraction forces
 Isaac Newton was the first
one who discovered the
earth‘s gravity force when he
was standing under a tree
and he found an apple
falling down to the ground.

6. Object’s weight
 It is the force of Earth’s gravity on the object.
Object’s center of gravity
 It is the effective point located at the centre of the object at
which the force of gravity affects the object.
W = m×g
weight = mass ×gravity(9.8 = 10 m/s2)

7. Example
 Find the weight an object of 100 kg.mass .
(g = 9.8 m/s2)

8. 2. Electromagnetic forces.
 They are the magnetic forces (magnetism) produced by the
effect of passing an electric current (the flow of electric charges)
through a coil.

9. Applications on electromagnetic forces.
 A) Electromagnet:
It is made up of an isolated
copper wire coiling around
a bar of wrought iron.
USES:
Electric winches
Electric bells.

10.  B) Electric Generator
(the dynamo)
 It converts the mechanical
energy into an electric energy.
 Uses:
 The dynamo of car or bike

11.  C) Electric Motor
 It converts the electric energy into
mechanical energy.
 Uses:
 The motor in fan and blender.
 The motor of toys

12. 3) NUCLEAR FORCES