Physics Newtons Third Law Of Motion
Newton’s Third Law of Motion
Importance of Newton’s Third Law of Motion
Newton’s Third Law of Motion states that for every action, there is an equal and opposite reaction. This law is fundamental to our understanding of the physical world and has numerous applications in various fields.
Applications in Everyday Life

Walking: When we walk, we push the ground backward with our feet. In response, the ground exerts an equal and opposite force forward on our feet, propelling us forward.

Swimming: When swimming, we push the water backward with our hands and feet. In response, the water exerts an equal and opposite force forward on our body, propelling us through the water.

Rocket Propulsion: Rockets propel themselves by expelling hot gases backward. According to Newton’s Third Law, the expulsion of these gases creates an equal and opposite force that pushes the rocket forward.
Applications in Engineering and Technology

Bridges and Buildings: Engineers design bridges and buildings to withstand various forces, including the force of gravity and wind. Newton’s Third Law helps engineers calculate the forces acting on these structures and design them accordingly.

Automotive Engineering: Engineers use Newton’s Third Law to design vehicles that can accelerate, brake, and turn effectively. The law helps determine the forces acting on vehicles and design components such as engines, brakes, and suspensions.

Aerospace Engineering: Newton’s Third Law is crucial in aerospace engineering for designing aircraft, rockets, and spacecraft. It helps engineers calculate the forces acting on these vehicles and design them for efficient and safe flight.
Applications in Sports and Recreation

Jumping: When jumping, we push the ground downward with our feet. In response, the ground exerts an equal and opposite force upward on our feet, propelling us into the air.

Kicking a Ball: When kicking a ball, we exert a force on the ball with our foot. In response, the ball exerts an equal and opposite force on our foot, causing the ball to move.

Playing Tennis: When hitting a tennis ball with a racket, the racket exerts a force on the ball. In response, the ball exerts an equal and opposite force on the racket, causing the ball to rebound.
Newton’s Third Law of Motion is a fundamental principle that governs the interactions between objects in the physical world. Its applications are vast and can be found in various fields, including everyday life, engineering, technology, sports, and recreation. Understanding and applying this law is essential for comprehending and predicting the behavior of objects in motion.
Newton’s Third Law of Motion Examples
Newton’s Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that whenever one object exerts a force on another object, the other object exerts a force of equal magnitude but opposite direction on the first object.
Here are some examples of Newton’s Third Law of Motion:
 When you push on a wall, the wall pushes back on you with the same amount of force. This is why you can’t push through a wall.
 When a rocket engine fires, the rocket pushes against the exhaust gases with the same amount of force that the exhaust gases push against the rocket. This is what propels the rocket forward.
 When a ball hits a wall, the ball exerts a force on the wall and the wall exerts a force on the ball. The force of the ball on the wall is equal in magnitude but opposite in direction to the force of the wall on the ball. This is why the ball bounces off the wall.
 When you walk, you push against the ground with your feet and the ground pushes back against you with the same amount of force. This is what propels you forward.
 When a car accelerates, the car pushes against the road with its tires and the road pushes back against the car with the same amount of force. This is what propels the car forward.
Newton’s Third Law of Motion is a fundamental law of physics that has many applications in everyday life. It is used to explain everything from how rockets work to how you are able to walk.
Limitations of Newton’s Third Law of Motion
Newton’s Third Law of Motion states that for every action, there is an equal and opposite reaction. While this law is generally true, there are certain limitations to its applicability.
1. NonContact Forces
Newton’s Third Law only applies to contact forces, which are forces that act directly between two objects in contact with each other. It does not apply to noncontact forces, such as gravitational forces or magnetic forces, which act over a distance without direct contact.
2. Variable Mass Systems
Newton’s Third Law assumes that the masses of the interacting objects remain constant. However, in some cases, the masses of the objects may change during the interaction, such as when fuel is burned in a rocket or when a ball of clay is thrown. In such cases, the law may not hold true in its simple form.
3. Internal Forces
Newton’s Third Law does not apply to internal forces within a single object. Internal forces are forces that act between different parts of the same object and do not involve any external interactions. For example, the forces between atoms and molecules within a solid object are internal forces, and they do not contribute to the net force acting on the object.
4. Relativistic Effects
At very high speeds approaching the speed of light, the effects of special relativity become significant, and Newton’s Third Law may need to be modified to account for relativistic effects. In such cases, the law may not hold true in its classical form.
5. Quantum Mechanics
At very small scales, such as the atomic and subatomic levels, the laws of quantum mechanics govern the behavior of matter, and Newton’s Third Law may not be applicable in its classical form. Quantum mechanics introduces additional complexities and uncertainties that require a different framework for understanding forces and interactions.
In summary, while Newton’s Third Law of Motion is a fundamental principle in classical mechanics, it has certain limitations when applied to noncontact forces, variable mass systems, internal forces, relativistic effects, and quantum mechanical phenomena. In these cases, more sophisticated theories and modifications may be necessary to accurately describe the interactions and forces involved.
Solved Examples on Newton’s Third Law of Motion
Example 1: TugofWar
Two people are engaged in a tugofwar. Each person is pulling on the rope with a force of 100 N. What is the net force on the rope?
Solution:
The net force on the rope is zero. This is because the two forces are equal in magnitude and opposite in direction.
Example 2: Rocket Propulsion
A rocket engine exerts a force of 1000 N on the rocket. What is the force exerted by the rocket on the exhaust gases?
Solution:
The force exerted by the rocket on the exhaust gases is also 1000 N. This is because the two forces are equal in magnitude and opposite in direction.
Example 3: Car Crash
A car collides with a wall. The car exerts a force of 10000 N on the wall. What is the force exerted by the wall on the car?
Solution:
The force exerted by the wall on the car is also 10000 N. This is because the two forces are equal in magnitude and opposite in direction.
Example 4: Horse and Cart
A horse pulls a cart with a force of 1000 N. What is the force exerted by the cart on the horse?
Solution:
The force exerted by the cart on the horse is also 1000 N. This is because the two forces are equal in magnitude and opposite in direction.
Example 5: Skydiver
A skydiver falls towards the Earth with a force of 980 N. What is the force exerted by the Earth on the skydiver?
Solution:
The force exerted by the Earth on the skydiver is also 980 N. This is because the two forces are equal in magnitude and opposite in direction.
Newtons Third Law of Motion FAQs
What is Newton’s Third Law of Motion?
Newton’s Third Law of Motion states that for every action, there is an equal and opposite reaction. In other words, when one object exerts a force on another object, the second object exerts a force of equal magnitude but opposite direction on the first object.
What are some examples of Newton’s Third Law of Motion?
Here are a few examples of Newton’s Third Law of Motion:
 When you push on a wall, the wall pushes back on you with the same amount of force.
 When a rocket engine fires, the rocket pushes against the exhaust gases with the same amount of force that the exhaust gases push against the rocket.
 When a ball hits a wall, the ball exerts a force on the wall and the wall exerts an equal and opposite force on the ball.
What are the implications of Newton’s Third Law of Motion?
Newton’s Third Law of Motion has a number of implications, including:
 The law of conservation of momentum: The total momentum of a closed system remains constant. This means that the total momentum of all the objects in a system is the same before and after any interactions between the objects.
 The law of action and reaction: For every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts a force of equal magnitude but opposite direction on the first object.
 The law of motion: An object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity, unless acted upon by an external force.
How is Newton’s Third Law of Motion used in real life?
Newton’s Third Law of Motion is used in a variety of reallife applications, including:
 Rockets: Rockets propel themselves by expelling hot gases from their engines. The force of the exhaust gases pushing against the rocket is equal to the force of the rocket pushing against the exhaust gases.
 Cars: Cars move forward by pushing against the ground with their tires. The force of the tires pushing against the ground is equal to the force of the ground pushing against the tires.
 Airplanes: Airplanes fly by pushing air downwards with their wings. The force of the wings pushing against the air is equal to the force of the air pushing against the wings.
Conclusion
Newton’s Third Law of Motion is a fundamental law of physics that has a wide range of applications in real life. The law states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts a force of equal magnitude but opposite direction on the first object.