Unit 1 : Chapter 4: Forces
Prepared By: Shakil Raiman

4.1: Nature and Types of Force

Forces at a distance: gravitational force, magnetic force, and electrostatic force
 Forces at a contact: Push, pull, tension, thrust, drag etc.

4.2 Gravitational Field Strength and
Weight
 Gravitational Field Strength: Gravitation force per unit mass is known as gravitational field strength.
 It is denoted by g. Unit: N/kg


W = mg
Unit: N

4.3: Newton’s Laws of Motion
 First Law: If there is no unbalanced force, there is no change of stages. That means, a still object will remain stationary and a moving object will keep on moving at a constant speed in a straight line.

4.3: Newton’s Laws of Motion
 Second Law: The rate of change of momentum of an object is directly proportional to the unbalanced force. The direction of the change in momentum is same as the direction of unbalanced force.
 Third Law: Every action (force) has an equal and opposite reaction (force).

4.4: Force Equation



Only unbalanced force can cause the acceleration.
In the formula,
F = ma ,
F = unbalanced force , m = mass of an object a = acceleration
In the formula,
F – f = ma
F = applied force f = opposing forces ( friction or air resistance)
Therefore, F – f = unbalanced force

4.5: Component of Force
 F x
= F cos 
 F y
= F sin 

F =  (F x
2 +F y
2 )

4.6: Newton Third Law Forces
 Similarity:
 Forces are of equal size


Forces are of same type
Forces acts along the same straight line
 Forces acts on same time
 Differences/Dissimilarity:
 Forces acts on two different object

Forces acts on opposite direction

4.7: Newton Third Law Pair Forces
 Example of one Force:
 The Earth exerts a downward gravitational force of
12 000 N on the car.
 Differences/Dissimilarity:

The car exerts a up ward gravitational force of 12
000 N on the Earth.

Thank You All
 Wish you all very good luck and excellent result.