# Chapter 9 – Force and Laws of Motion

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

Although Newton’s laws of motion might sound simple to us today, they were deemed groundbreaking centuries ago. The three laws of motion allow one to grasp how objects respond as they remain stationary, when they move, and when forces work upon them. This article is a review of the Force and Laws of Motion of Sir Isaac Newton and a rundown of what they say.

#### What is Force?

Force is an effort that alters the status of the entity at rest or at motion. It will adjust the trajectory and velocity of an object. Force may also change the shape of an object.

Balanced and Unbalanced Forces

There is no net effective force acting on the object when balanced forces are applied to the object. Balanced forces do not trigger a shift of motion.

Unbalanced forces acting on an object change its velocity and/or direction of motion. The object moves in the direction of the force of the highest magnitude.

Net force

When several forces operate on the body, they can be dissolved into a single component known as the net force operating on the entity.

Force of Friction

The force which opposes the relative motion is called friction. It occurs between the surfaces in contact with each other.

Example: Anytime we want to push a table and it doesn’t move, that’s because the frictional force is balanced.

#### First Law of Motion

A body appears to be in a state of rest or uniform motion in a straight line until it operates through an external unbalanced force. The First Law is also referred to as the Law of Inertia.

Inertia

Basically, all objects appear to avoid a change in the state of motion or rest. This is called inertia. Not all bodies have the same inertia. Inertia relies on the body’s mass. The mass of an entity is the measure of its own inertia.

More mass is equal to more inertia, and vice versa.

Momentum

The effects produced by objects rely on their mass and velocity. The momentum of an object is given by the product of its mass and its velocity. P = mv. Vector quantity has both magnitude and direction.

#### Second Law of Motion

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

Δp / t . α . m(v−u) / t

= Δp / t . α . m . a

= F . α . m . a

Therefore, F = k . m . a

For 1 unit of force with a weight of 1 kg and an acceleration of 1m/s2, the value of k is 1.

F = m . a (mass x acceleration)

#### Third Law of Motion

The third rule of motion provides the description of how the body’s position and motion are changed by a force imposed on it.

As two bodies meet, they both exert an equivalent amount of force to each other, where the forces are in entirely opposite directions. To properly grasp Newton’s third law, we should take a textbook, push it down on a surface, and see the book come to rest on the surface. The leaf of the book applies a downwards force proportional to its weight to the surface. The surface still has an equal and opposite force on the book, forcing the book to push in the opposite direction. This is so because when a book is laid on a surface, it subtly deforms the surface, having the surface push down on the book like a coiled spring. Newton’s Third Law of Motion means that the conservation of momentum exists.

#### Conservation of Momentum

The portion of the world selected to be studied is named the system.

Anything outside of the system is called the environment.

For example, a vehicle traveling at a constant speed may be called a system. Both forces inside the car are internal forces, and all forces operating on the car from the environment are external forces such as friction.

The law of conservation of momentum says that the cumulative momentum of an isolated system is conserved. An isolated system has the total external force on the system as zero.

#### Conclusion

In this chapter, we understood what is force and what are the three laws of motion. We also talked about inertia and mass, and the principle of conservation of momentum which plays a very vital role when we talk about force and laws of motion.

#### FAQs

1. What are the 3 laws of motion?

Newton’s laws of motion attribute the motion of a body to the forces operating on it.

• In the first law, an object does not alter its motion until a force operates on it.
• In the second law, the force on an object is proportional to the mass periods of acceleration.
• In the third law, as two objects meet, forces of similar magnitude and opposite directions are directed to each other.

2. What is stated in the 2nd Law of Motion?

The second law of motion states that as a result of the net force, the acceleration of the object is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

3. What is Newton’s third law equation?

If A is an object and it exerts a force FA on the second object which is B then the third law equation becomes FA = −FB.

4. What is Newton’s third law example?

An example of the third law can be that when you strike a wall with a certain amount of force, the wall reflects the same amount of force.

5. What is the relationship between force and speed?

Force = mass x acceleration

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