JSS 2: FORCE

Force is an action  that changes or tends to change the state of rest or of uniform motion in straight line. 

The S.I unit of force is the newton (N).

Force is measured using an instrument called a spring balance or Newton meter.

Examples of Force

i. Pushing a door open.

ii. Pulling a bucket from a well.

iii. Kicking a football.

iv. Lifting a school bag.

v. Pushing a table etc

 Types of Force

The two types of force are:

(1) Contact force 

(2) Non-contact (or Field) force

Contact Force

This is a force that acts when objects are physically touching each other.

Examples of contact force include:

I. Push

II. Pull

III. Friction: Force that opposes motion between surfaces.

IV. Tension: Force acting through a rope or string.

B. Non-Contact Force

This is a force that acts without physical contact between objects.

Examples include:

I. Gravitational force: Force that pulls objects towards the Earth.

II. Magnetic force: Force of attraction or repulsion between magnets.

III. Electrostatic force: Force between electrically charged objects.

Relationship between Force, Mass and Acceleration

Force is related to mass and acceleration.

The formula is:

Force = mass × acceleration

F = ma

Where:

F = Force in newtons (N)

m = Mass in kilograms (kg)

a = Acceleration in metres per second squared (m/s²)

Simple Calculations

Example 1

A body has a mass of 5 kg and accelerates at 2 m/s². Calculate the force acting on it.

Solution:

Force = mass × acceleration

F = 5 × 2

F = 10 N

Therefore, the force is 10 N.

Example 2

A force of 20 N acts on an object of mass 4 kg. Calculate its acceleration.

Solution:

Force = mass × acceleration

20 = 4 × a

a = 20/4

a = 5 m/s²

Therefore, the acceleration is 5 m/s².

Example 3

A force of 30 N acts on a body with an acceleration of 5 m/s². Find its mass.

Solution:

Force = mass × acceleration

30 = m × 5

m = 30/5

m = 6 kg

Therefore, the mass is 6 kg.

Difference Between Mass and Weight

Mass

Mass is the amount of matter that is present in an object.

S.I unit of mass is kilogram (kg).

Weight 

Weight is the force with which gravity pulls an object towards the earth.

The S.I unit of weight is the newton (N).

Weight can be calculated using:

Weight= mass × acceleration due to gravity 

W = m × gk.

Where:

W = Weight in newtons (N)

m = Mass in kilograms (kg)

g = Acceleration due to gravity, approximately 10 m/s² for simple calculations.

Example:

Find the weight of a student whose mass is 40 kg.

Weight= mass × acceleration due to gravity 

W = mg

W = 40 × 10

W = 400 N

Therefore, the student's weight is 400 N.

Class activities 

(1). Calculate the force required to accelerate a 10 kg object at 3 m/s².

(2). A force of 24 N acts on a body of mass 6 kg. Find its acceleration.

(3). Calculate the weight of a 50 kg object (g=10 m/s²)