In this knowledge article, we shall get acquainted with the concept of Force and Laws of Motion.

## Definition of Force

Force is something that enables us to do any work. It is the push or a pull acting on a body, which cannot be seen but can only be felt. It is a vector quantity because it can be described by both magnitude and direction and the SI unit of Force is Newton represented by the symbol F.

### Examples of Force

• Push or pull to open a door
• Lifting a box
• Pulling a trolley

Force can be judged by the various effects it can produce in several bodies.

### The Effects of Force and be enumerated as follows

• Force can put a stationary body to motion- This means that when an adequate amount of force is applied to a non-moving body then the latter moves. For example- a box lying on the floor can be moved by pushing it i.e by applying force on it
• Force can put a body in motion to rest – This means it can stop a moving body. For example- a car in motion can be stopped by applying brakes to it
• The speed of a moving body can be changed by applying force on it – by putting force on the accelerator the speed of a moving car can be increased and by applying brakes the speed can either be decreased and eventually even stop the moving car
• Force can change the direction of a moving body- For example, id adequate amount of force is applied on the moving football to the desired direction then the ball will move in the direction it has been kicked
• Force can change the shape and size of an object – For example by hammering a solid block of rock, a statue can be made.

## Types of Force

Force can be further categorized into two types-

• Balanced Forces

Balanced forces are the one where not all the above-mentioned effects of force holds true, which means that the result of applied forces is equal to zero. Balanced forces do not cause any change in the state of the object it is applied upon i.e. the object in which force is applied the state doesn’t change from motion to rest or vice-versa, however, balanced forces can change the shape and size of an object. Such kind of forces is equal in magnitude but in opposite directions. For example- Two people putting equal force in a tug-off war or a log floating on water.

• Unbalanced Forces

Unlike balanced forces, unbalanced forces are ones where the resultant applied forces is greater than zero i.e. the forces acting on the object is not same.

The features of Unbalanced forces are-

• It can move a stationary body
• Increase or decrease the speed of a moving body
• Put a moving to rest
• Change the shape and size of the object on which force is applied upon

### Other Types of Forces are

• Muscular Force
• Gravitational Force
• Frictional Force
• Air Resistance

## Laws of Motion

What is Motion?

Motion is described as a change in the position of an object over time. It is described in terms of displacement, distance, velocity, acceleration, time, and speed.

### Galileo laws of motion

Galileo laid the foundation of laws of motion, it was because of his studies and research that the concept of motion in terms of velocity was developed, he also developed the idea of force as the cause of motion.

Galileo’s laws of Motion stated that the natural state of an object is rest or uniform motion, i.e. objects always have a velocity and sometimes this velocity has a magnitude of zero = rest. He also stated that an object moves with a constant speed when no forces act on them, which means that if an object is moving on a frictionless ground and no other force is acting upon it, the object would be moving forever. That is there is no unbalanced force working on the object, but practically this is not possible because always some form of force always acts on an object.

### Newton’s Laws of Motion

Forming Galileo’s studies as the basis Newton expanded the Laws of Motion. Newton’s laws of motion laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and the resulting motion in response to these forces.

Newton has given us three Law’s of motion which are-

Newton’s First Law of Motion:

An object will either remain at rest or continue to move at a constant speed in a straight line unless acted upon by an external force which can change its state of rest or motion.

This law is supported by the concept of Inertia which a property of a body due to which it resists the change in its state of rest or of uniform motion. The inertia of an object is measured by its mass which is directly proportional to each other.

Application of this Law

• A person standing in a bus falls back when the bus starts moving suddenly. This happens because the person and bus both are in rest while the bus is not moving, but as the bus starts moving the legs of the person start moving along with bus but the rest of his body has a tendency to remain in rest because of inertia. Because of this person falls backward.
• When one shakes a tree, it moves to and fro but the fruits laden on it remains at rest due to its inertia of rest, that’s why fruits drop off the tree.

Newton’s Second Law of Motion:

The rate of change of momentum is directly proportional to the force applied to the object in the direction of a force.

Momentum is the quantity of motion of a moving body. In a basic sense, it is the power of the motion of the object. It is the product of the mass of the body and its velocity.

Application of this Law

• While trying to catch a cricket ball coming with a great speed, a fielder pulls his hand backward to reduce the momentum of the ball with a little delay applying Newton’s Second Law of motion.

Newton’s Third Law of Motion:

There is always a reaction to every action in opposite direction and of equal magnitude. In basic terms, it means whenever a force is applied to a body, that body also applies the same force of equal magnitude and in opposite direction.

Application of this Law

• When a person walks he pushes the ground in the backward direction and in the reaction the ground also pushes the person with equal magnitude of force but in opposite direction. This enables him to move in forwarding direction against the push.

Know more about the significance of Force in Physics, here.

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