Force

A force is an interaction that causes a change. In mechanics, a force is an interaction that causes a change in velocity (an interaction that causes acceleration)

SPECIFIC OBJECTIVES

By the end of this topic, you should be able to

1. Explain the concept of force
2. State the SI unit of force
3. Identify fundamental types of force
4. Describe the properties of each type of fundamental forces.
5. Identify the properties of forces
6. Justify the effects of force on materials.

CONCEPT FORCE

For better understanding of this concept, let’s ask ourselves the following question.

1. What causes/makes a body at rest to move?
2. What causes the same body in motion to stop?

The answers to these questions, is of course that a force is required to do so. Here, an applied force to a body can cause the body at rest to move or if already moving a body application of force can do the following when applied to a body.

1. Force can cause a change in the way the object moves
2. Change its sixe or shape
3. Change the direction in which an object is moving.

Definition:

A force is defined as a push or pulls experienced by an object.

The force is usually described in terms of its size (magnitude) and direction.

The SI unit of force is a Newton (N).

A Newton (1N) can be defined as the amount of force required to give a mass of one kilogram (1kg) an acceleration of 1m/s²

MEASURING INSTRUMENT (DEVICE)

The instrument that is used to measure the amount of force that is exerted on an object is called spring balance.

A spring balance can be used to measure small forces. It consists of a coiled spring fixed to the other end with a hook at the other end. The body upon which the force acts is attached to the hook. The distance through which the spring is stretched is directly proportional to the force applied by the balance.

A pointer is attached to the spring and the force is indicated on a calibrated scale.

Types of forces

There are two main types of forces namely;

1. Fundamental forces
2. Non fundamental forces

Fundamental types of forces

Definition:
Fundamental forces are the basic forces in nature that cannot be explained by the action of another force.
There are four types of fundamental forces. These include:-

1. The force of gravity
2. The electromagnetic force
3. The strong nuclear force
4. The weak nucleus force

Force of gravity (weight)

The force of gravity is the pull by which the earth, moon and other very large bodies attract other objects towards themselves. It is commonly referred to as the weight of the object that is attracted.
All objects on the earth experience a force of gravity that is directed downwards towards centre of the earth. The earth’s gravitational pull is so great that it is able to hold most things firmly on the ground
In mechanics, a freely falling body in the air moves down irrespective of its mass. This is due to force of gravity.

For example
A fruit fall from a tree because the earth exerts gravitational force on it. The force of gravity on the earth is always equal to the weight of the object (body)

                       Force of gravity, W = mass (m) x gravitational acceleration (g)
                                          W= mg

Where acceleration due to gravity on the earth, g = 9.8m/s²
Conclusive, we can say that the force of gravity has the following properties.

1. It pulls (attracts) objects forwards the centre of the earth.
2. It is directly proportional to the mass of the object. This means that the greater the mass the greater the pull of gravity.
3. It is strong when the mass is closer to the centre of the earth.

NB: It should be noted that the weight of an object is directly related to its Mass.
  Weight, W = mass x g
                        = mg

The g above has two meanings;-

1. It is the gravitation’s field strength (10N/Kg)
2. It is the acceleration of free fall (10m/s²

Properties of gravitational force:

The following are the properties of gravitational force

• It is always attractive
• It is the weakest force among the four basic forces.
• It is a central force (gravitational force between two objects acts along the line joining the centres of the objects
• It operates over very long distance

2. Electromagnetic force

This force includes both electric and magnetic force. It is relatively strong.
Examples where electromagnetic forces are involved include;-

• In the formation of molecules of a substance. Atoms attract each other to form molecules. This is due to electromagnetic force.
• In two parallel wires carrying current. If places near each other, the electromagnetic force acts on the wires.

Properties of electromagnetic force include

• It may be attractive or repulsive is nature
• It is a central force
• It is stronger than gravitational force
• It is also a long-range force (operates over a very long distance.)

3. Strong nuclear force.
This is the force, which holds of the constitutions (sub atomic particles) of the atomic nucleus. It acts within the nucleus of the atom.

Properties of the strong nuclear force:

1. It is basically an attractive force
2. It is a non-central force (does not act at the centre)
3. It is stronger than gravitational force
4. It is a short-range force that is it operates only up to distance of the order of 10^-14m

4. Weak nuclear force.
This is the force which appears only in certain nuclear processes.

This force has the following properties:

1. It is much stronger than the gravitational force but weaker than the strong nuclear force and electromagnetic force
2. It acts on small ranges of up to 10^-17m

CLASS ACTIVITY

1. Define the term force and give its SI unit.
2. Mention four fundamental types of force that you know.
3. Define the following terms;
   i.  Force of gravity
   ii. Strong nuclear force
   iii. Electromagnetic force
4. A body has a mass of 40kg. Find its weight.