 # Force Definition - Types and Units What is Force?

A Force refers to push or pull of an object. Push and pull comes from the objects interacting with one another. Terms like stretch and squeeze can also be used to denote force. Force can be defined as an external agent capable of changing the state of rest or motion of a particular body. It has a magnitude and a direction. The direction towards which the force is applied is known as the direction of the force, and the application of force is the point where force is applied. The Force can be measured using a spring balance. The SI unit of force is Newton(N).

The Force has different effects and here are some of them.

Force can make a body which is at rest to move. It can stop a moving body or slow it down. It can accelerate the speed of a moving body. It can also change the direction of a moving body along with its shape and size. There are two types of forces based on their applications. They are contact forces and non-contact forces.

Types of Forces

1. Contact Force
2. Non-Contact Force

Contact Force

Forces which act on a body either directly or through a medium are called contact forces. The examples of contact forces are a Muscular force, mechanical force and Frictional Force. We can make use of muscular force of animals like bullocks, horses and camels to get the activities done. The frictional force is another type of contact force which acts between a pair of a surface in contact and tends to oppose the motion of one surface over the other.

Non-Contact Force

Forces which act through spaces without making direct contact with the body are called non-contact forces. The examples of non-contact forces are the Gravitational force, electrostatic force and magnetic force. The force exerted by a magnet on other magnets is called magnetic force. Magnetic force and electrostatic force act on an object from a distance, that’s the reason they are non-contact forces. The strength of gravity is an attractive force which is exerted by the Earth on objects which make them fall to the land. The weight of a body is the force which is pulled by the earth towards the centre.

The magnitude of the force is given by the product of the mass of the object (m) and its acceleration (a). Mathematically it can be expressed by the equation

F = ma

The CGS unit of force is dyne, and its SI unit is newton (N). The line along which a force is acting on an object is called the line of action of the force. The point where the force is acting on an object is called the Point of application of the force. The force which opposes the relative motion between the surfaces of two objects in contact and acts along the surfaces is called the force of friction.
Galileo experimentally proved that objects that are in motion move with constant speed when there is no force acting on it. He could note that when a sphere is rolling down an inclined plane, its speed increases because of the gravitational pull which is acting on it.
When all the forces acting on an object are balanced, the net force acting is zero. But, if all the forces acting on a body result in an unbalanced force, then the unbalanced force can accelerate the body, which means that a net force acting on a body can either change the magnitude of its velocity or change the direction of its velocity. For example, when many forces act on a body, and the body is found to be at rest, we can conclude that the net force acting on the body is zero.

#### Practise This Question A lab assistant has to write the equation of a spring block system doing SHM. At t = 0 the block is in the condition as shown above.He writes the equation as x=A sin(ω t+ϕ). Find the value of ϕ?