Newton’s Third Law of Motion

Table of Contents

Sir Isaac Newton proposed three fundamental laws of motion about three centuries ago. The science of dynamics and astronomy are based on these laws. There have been few achievements in human history that can compare to these laws. Because these are only claims, formal verification of these rules is impossible. Newton himself uttered the following words:

‘Axiomata Sive Leges Motus’ is a Latin phrase that means “Axiomata Sive Leges Motus (the axioms or laws of motion). However, we are justified in adopting them because everything they anticipate matches the experimental findings.

In this article, our primary topic is Newton’s third law of motion. However, we will also cover all three laws of motion. The following are the laws:

Law of Inertia, the first law of motion

This law states that “everything persists in its state of rest or of uniform motion in a straight line unless forcibly compelled to change by force. ” In plain language, this law is stated as follows:

Unless and until it is compelled by an external force to change, everyone in this world remains in a state of rest or uniform motion in a straight line.

Newton’s first law asserts that unless driven to change its condition by an external force, every object will remain at rest or in uniform motion in a straight line. A condition of motion is subject to inertia when it tends to resist change. An object has no net force operating on it (if all the external forces cancel each other out). The object’s velocity will then remain constant. If the velocity is zero, the item is said to be at rest. Any object whose velocity has been changed due to an external force will change as a result.

Aerodynamic inertia examples include:

When a pilot changes the throttle setting on an engine, the airplane moves.
The movement of a ball as it falls through the sky.
The launch of a model rocket into the atmosphere.
When the wind changes, a kite’s motion alters.

The Second law of motion

The rate of change of momentum of a body is proportional to the applied force and occurs in the force’s direction of action.

The second law states that force is defined by the change in momentum (mass times velocity) per change in time. Objects have momentum equal to their mass times their velocity multiplied by their mass.

F=ma

The motion of an airplane caused by aerodynamic forces, aircraft weight, and propulsion is an example of a force involving aerodynamics.

The third Law of motion

Action and reaction are equal and opposite.

Discussion of The Third Law of Motion

We can tell whether a net force operates on a body using the first rule of motion, and if it does, we can compute the force using the second law. As a result, the first and second laws are concerned with the motion of a single body. Because it is about pairs of mutually interacting bodies, Newton’s third law of motion is unique. Despite the fact that we have already expressed this law in a normal manner, we must state it again in order to avoid misunderstanding.

Let’s assume there are two bodies namely X and Y. If a force is exerted by body Y on a body X that is FXY , then the body X exerts a force on the body Y that is FYX of the same magnitude but in the opposite direction and along the same line of action.

Some Important aspects about Newton’s third law of motion

Because they act on distinct bodies and never on the same body, the forces of action and response cannot balance.

This law holds true whether the two bodies are stationary or moving, in contact or acting at a distance.

The third law does not imply that action and reaction have the same impact. The forces on the face and the fist are equal when one fighter punches another in the face, yet the effects are vastly different.

Image Source: Self Made

Also read: Multiplication of Vectors by a Real Number

Let’s have a look at some of the examples of Action and Reaction Forces

Nature contains a wide range of action-reaction force pairs. Consider a fish’s ability to move across the water. Water is pushed backward by the fins of fish. Conversely, pushing the water will simply have the effect of speeding it up. Because mutual interactions produce forces, the water must also be pushing the fish ahead, propelling it through the water.
There is the same size force on the water as there is on the fish, and the force on the water (backward) is the opposite of the force on the fish (forward). There is an equal (in size) and opposite (in direction) response force for every action. Swimming is possible because of the coupling between action and reaction forces.
When a bat strikes a ball, it puts a significant amount of force on the ball. The ball exerts a response force on the bat, according to Newton’s third law, which is a force of the same size and opposite direction.
Because there is no friction, a man sitting in the middle of a frozen pond on totally frictionless ice cannot walk to the shore. He can, however, travel to the shore by tossing an object he has in his possession with a lot of power in the opposite direction of where he wants to go. This force’s reaction propels the individual forward. Because the ice is completely frictionless, the man will only come to a complete halt when he hits the beach.
When we pull a rope fastened to a nail in the wall with our hand, the action is the force exerted by the hand on the rope, and the reaction is the force exerted by the rope on the hand.

In classical physics, Newton’s laws of motion are extremely important. Newton’s laws can be used to deduce a wide variety of principles and findings. The first two rules deal with the type of motion that a system produces as a result of a set of forces. These laws can be interpreted in a variety of ways, and going into the technical specifics of the interpretation is slightly uninteresting and unpleasant at first. Before we relate mass, force, and acceleration, we must first define them precisely. These definitions, in turn, need the application of Newton’s laws. As a result, these laws function as definitions to some extent. In this article, we have covered the Laws of motion and have given special attention to Newton’s third law of motion, Action reaction pair, and discussed examples of Aerodynamic forces. If you like our content and want more such content ahead, stay tuned!

Laws of Motion JEE and NEET Past year questions

Question 1: A ship of mass 3 x kg is initially at rest, and then 5 x N pulls it through a distance of 3 m. In the case of negligible water resistance, the speed of the ship would be (JEE- 1980).

Answer: a=F ⁄ m 5 × 10⁴ ⁄ 3 × 10⁷ = (5 × 3 )10^-3m s^-2

Velocity v=(2 as) ^1⁄2 2 × (5 ⁄ 3 ) ^{1 ⁄ 2}10^-33

=0.1 ms^-1

Question 2: State whether True/False

Figures (a) and (b) have the same pulley arrangement. The mass of the rope is negligible. In Fig. (a), a mass 2 m is attached to the end of the rope so that the mass m can be lifted. In Fig. A constant downward force of F = 2 mg is applied to the other end of the rope to raise m. In both cases, m accelerates at the same speed. (1980 2 M)

Image Source: Arihant 40 years chapter wise JEE physics solved Book

Answer: In their cases, a=Net pulling forces ⁄ Total Mass

Net pulling force in both the case is: 2 mg-mg = mg

Mass to be pulled in case (a) is 3 m and in case (b) is m, therefore, a₁=mg ⁄ 3 m=g ⁄ 3

and , a₂=mg ⁄ m=g

Therefore a₁<a₂

Hence the right option is False.

Question 3: A person is standing in an elevator. In which situation does he find his weightless?

When the elevator moves upward with constant acceleration
When the elevator moves downward with constant acceleration
When the elevator moves upward with uniform velocity
When the elevator moves downward with uniform velocity

Answer: Option (b) When the elevator moves downward with constant acceleration

Gravitational acceleration always operates downward. W=m(ga) is the consequent weight, which is smaller than the original weight mg, when the elevator moves downward with constant acceleration, i.e. when the resultant acceleration is downward. As a result, the individual feels weightless.