Forces: meaning, types and example

People do many kinds of work every day. They work out, walk, talk, run, jump, eat, drink and whatnot. However, if we look at these activities generally one at a time, all these activities involve either a push or a pull. For instance, while opening the door, we pull the handle and while closing it, we push the handle. While jumping, we push our feet up. While walking, we push our feet backwards with our feet. 

Scientifically, all these activities require the exertion of a force. A force is essential to do all the activities mentioned above. A force is a push or a pull, acting on an object. It is a vector quantity, that is, it also involves a direction. Besides the direction of force, the numerical value associated with a force is called its magnitude.

Types of Forces

Force acts as the external agent that facilitates motion. Just like there are different types of motion, force is also classified into different types.

One basis of classification is contact or interaction. One important thing to be noted about forces is that an interaction between the objects is necessary for a force to come into play. The interaction occurs between the object exerting the force and the object on which the force acts. Interaction does not necessarily mean contact. Some forces require contact for this interaction while others do not. The non-contact forces act over a distance. Accordingly, they have been classified into contact and non-contact forces. The following are some examples of contact and non-contact forces:

• Contact Forces

1. Frictional force
2. Muscular force
3. Normal force
4. Air Resistance force

• Non-Contact Forces

1. Gravitational force
2. Electromagnetic force
3. Strong Nuclear force
4. Weak Nuclear force

However, on further analysis of the topic, it can be observed that these contact forces can actually be just included in the list of non-contact forces since all of them are actually just different manifestations of the same non-contact forces. Take muscular force and mechanical force for instance. Both are contact forces. But when two objects are in contact, the electrons of the objects actually repel each other due to like charges. Therefore, nothing is actually in contact, so to speak. Therefore all contact forces actually just fall under the bracket of electromagnetic forces.

Hence non-contact forces are the only actual forces in existence. The scientists have grouped the non-contact forces under four fundamental forces. The four fundamental forces in existence are as follows-

1. Gravitational force
2. Electromagnetic force
3. Weak Nuclear force
4. Strong Nuclear force

Both sets of forces are studied separately and have their own relevance. For most general purposes, one does not need to be concerned with microscopic interactions. Hence, contact forces are also helpful and their study helps us to understand everyday phenomena.

Units of Force

There are several units of force according to different systems of units. According to the SI, the unit of force is Newton(N). One newton is defined as the amount of force that can produce an acceleration of 1 m/s on a body of mass 1 kg. The SI unit of force is derived from the SI units of mass(kg) and acceleration(m/s²) which are used to calculate force as we will soon see. Therefore one newton equals 1 kg.m s^-2.

The other units of force include dyne(Dyn) in the CGS system and poundal (pdl) in the FPS system of units.

Balanced and Unbalanced Forces

Since force is a vector quantity, it also involves direction associated with the magnitude. When a single force acts on a body, it moves with no complications. However, when multiple forces act on the same object, the effect of the force is determined on the basis of the net force acting on the object. The net force is nothing but the total amount of force actually acting on the body. It is different from the applied force. Not all of the applied force actually acts on the body. Some of it might be cancelled by opposing forces or unused because of the direction.

Broadly, when two or more forces act on the same object in the same direction, they add up. On the other hand, when two or more forces act in opposite directions on the same object, they cancel each other out. If one of the forces has a higher magnitude, the body will move in the direction of that force, with whatever magnitude is left after the cancelling out of forces. When the two opposing forces are equal and cancel each other out completely, they are said to be balanced. When the opposing forces do not cancel each other out completely, they are said to be unbalanced. Unbalanced forces bring about a change in the state of motion of the object. 

Newton’s Laws of Motion

The renowned physicist Sir Issac Newton drafted the laws of motion based on a set of observations made by him regarding everyday phenomena. These laws enable us to understand and predict the motion of objects that we see around us. These laws were formulated after a thorough study of forces. 

•  First Law of Motion- The law states that an object at rest remains at rest and an object in motion remains in motion at a constant force unless compelled to change that state by an external unbalanced force. All the objects possess a property of resisting motion, called inertia.
• Second Law of Motion- The rate of change of momentum of an object is directly proportional to the applied force and takes place in the direction of the force. Momentum is the product of mass and velocity. The derivation of this law gives us the formula to calculate force, which is:

F=ma

• Third Law of Motion- Every action has an equal and opposite reaction and they both act on two different objects.

Conclusion

A push or a pull acting on an object is known as force. The application of a force can change the state of motion of an object or change the shape of the body. The total amount of force acting on the body is called net force. There are three laws of motion that are based on the study and analysis of forces.