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2. Force is a any influence that causes an object to undergo a certain
change, either concerning its movement, direction, or geometrical
construction. In other words, a force can cause an object
with mass to change its velocity (which includes to begin moving
from a state of rest), i.e., to accelerate, or a flexible object
to deform, or both.

3. 1. Contact Forces
Contact forces are forces which exist between objects that
are in contact.
Types:
a. Normal Reaction
The normal reaction
by the table surface on
the book is
perpendicular to the
surface.
The push exerted by a surface on an object pressing on it –
this push is always perpendicular to the surface.
Types of Forces

4. b. Friction
The force that opposes or tends to oppose motion between surfaces
in contact.
The friction between the soles of
our shoes and the floor prevents
us from slipping when walking.
c. Tension
The pull exerted by a stretched spring, string or rope on an
object attached to it.
The tension in the spring pulls
the object downward

5. 2. Non-contact Forces
Non-contact forces are forces which do not require objects to be in
contact to exist.
Types:
a. Gravitational Force
The pull exerted by the Earth’s gravity on any object (i.e. weight)
The gravitational force
pulls the apple
downward from the tree
towards the ground.

6. b. Electric Force
The attractive (i.e. pull) or repulsive (i.e. push)
forces between electric charges.
Attractive electric forces between
unlike charges.
Repulsive electric forces between like
charges.

7. c. Magnetic Force
The attractive (i.e. pull) or repulsive (i.e. push) forces
between magnets.
Repulsive magnetic force
between like poles.
Attractive magnetic force
between unlike poles.

8. A force is a vector – it has both magnitude and direction. Its SI unit is
newton (N). We can use vector diagrams to add up forces with
different magnitudes and directions.
In a vector diagram, a vector quantity is represented by an arrow.
The direction of the arrow indicates the direction of the vector.
Vector Diagrams

9. When we add two or more vectors, we cannot add their
magnitudes only. We need to find a single vector that
produces the same effect as the vectors combined. The single
vector is called the resultant vector.
1. Addition of parallel vectors
How do we add vectors?

10. 2. Addition of non-parallel vectors
There are two methods of adding non-parallel:
a. Parallelogram method
b. Tip-to-tail method
a. Parallelogram method

11. b. Tip-to-tail method

12. 1. Balanced forces and Newton’s first law
Newton’s first law of motion states that every object will continue in its state of
rest or uniform motion in a straight line unless a resultant force acts on it.
If the resultant force acting on an object is zero, we say the forces acting on the
object are balanced.
Newton’s Laws

13. 2. Unbalanced forces and Newton’s second law
Newton’s Second Law of Motion states that when a resultant force
acts on an object of a constant mass, the object will accelerate in
the direction of the resultant force. The product of the mass and
acceleration of the object gives the resultant force
If the resultant force acting on an object is not zero, we say
the forces acting on the object are unbalanced.

14. F = m.a
F = resultant force (in N)
m = mass of object (in kg)
a = acceleration (in m s-2)
Newton’s Second Law of Motion tells us that:
1. A resultant force F on an object produces an
acceleration a;
2. Doubling the resultant force F on an object doubles
its acceleration a;
3. With the same resultant force F, doubling the mass m
halves the acceleration a.

15. Examples
1. A block of mass 2.0 kg is being pulled on a horizontal bench by a force
of 12 N. If the block accelerates at 5.0 ms-2, what is the frictional force f
between the block and the bench?
Solution:
F = m.a
= 2 kg x 5.0 ms-2
= 10 N
Friction = 12 N – 10 N
= 2 N

16. 2. Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the
car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's
Second Law, you can compute how much force Mike is applying to the car.
Solution:
F = m.a
= 1000 kg x 0.05m/s/s
= 50 N

17. Thank You