Newton's Laws of Motion - Understanding How Forces Affect The Movement of Objects in Our Everyday Lives
Newton's Laws of Motion form the foundation of classical mechanics, describing how objects move and interact under the influence of forces. These laws explain the behaviour of stationary and moving bodies, making them essential for understanding everything from everyday motions to complex mechanical systems. Sir Isaac Newton formulated the laws of motion in the year 1686 in his book ‘Principia Mathematica Philosophiae Naturalis. In this guide, we’ll explore the three laws, their applications, and how they help us analyse motion in various scenarios for JEE Main 2025.
What are Newton's Laws of Motion?
The Three Newtons Laws of Motion are:
Newton’s first law (Law of Inertia) - Newton's first law of motion states that, if a body is in the state of rest or is moving with a constant speed in a straight line, then the body will remain in the state of rest or keep moving in the straight line, unless and until it is acted upon by an external force.
Newton’s second law (Force and Acceleration) - Newton's 2nd law of motion states that the rate of change of momentum of a body is directly proportional to the force applied on it, and the momentum occurs in the direction of the net applied force.
Newton’s third law (Action-Reaction) - According to Newton's third law of motion, to every action, there is always an equal and opposite reaction.
First Law of Motion (Law of Inertia)
This property of a body unable to change its state is called Inertia. Galileo Galilei first formulated the law of inertia for the horizontal motion of planet Earth. Later on, it was generalised to René Descartes. Before Galileo, it was believed that a force is required to keep a body moving. Galileo deduced that a body can't change its state unless acted by force (like friction).
The state of motion or rest cannot be changed without applying force. If a body is moving in a particular direction, it will keep moving in that direction, until an external force is applied to stop it.
Second Law of Motion (F=MA)
Newton's second law gives a quantitative description of force. The momentum of a body is equivalent to the product of its mass and velocity. To speak, momentum is a vector quantity having both velocity and magnitude. When force is applied to a body, it can either change its momentum, its velocity or both. Newton's second law of motion is one of the most important laws of classical physics.
For a body of constant mass m, Newton's law formula is given as,
F = ma,
Where ‘F’ is the applied force, and ‘a’ is the acceleration produced, and m is the mass of the object
If the net force acting on a body is positive, the body gets accelerated. Conversely, if the net force is 0, the body doesn't accelerate.
According to the second law of motion, if force is applied to two different objects of different masses, different accelerations (change in motion) are produced. The body with less mass accelerates more.
The effect of a force of around 15 Newton on football will be much more significant as compared to the impact of the same force applied to move a car. This difference is due to the difference in the masses of the two objects.
Third Law of Motion (Action-Reaction)
According to Newton's third law of motion, to every action, there is always an equal and opposite reaction. Also, the action and reaction occur in two different bodies. When two bodies interact with each other, they exchange force, which is equal in magnitude but act in opposite directions. This law has a huge application in static equilibrium where the forces are balanced, and also for objects which undergo uniform accelerated motion.
For example, a laptop kept on a table exerts a downward force, which is equal to its weight on the table, and consequently, the table exerts an equal and opposite force on the laptop. This force comes into play because the weight of the laptop slightly deforms the table, and in return, the table pushes back the laptop.
Newtons Laws of Motion Examples
Here are simple examples to help understand Newton's three laws of motion:
1. Newton's First Law (Law of Inertia):
Example: A stationary ball on a flat surface will stay at rest until someone kicks it. Similarly, a moving car will keep moving unless brakes are applied or another force stops it.
Real Life: Wearing seat belts in a car prevents passengers from moving forward during a sudden stop.
2. Newton's Second Law (Force and Acceleration):
Example: A shopping trolley accelerates faster when pushed with more force. A heavier trolley needs more force to move it at the same speed.
Real Life: A cricketer applies less force to throw a tennis ball than a cricket ball because the cricket ball is heavier.
3. Newton's Third Law (Action and Reaction):
Example: When you jump off a small boat, the boat moves backwards as you push it. Your push (action) causes the boat to move in the opposite direction (reaction).
Real Life: Rockets launch into space by pushing exhaust gases downward, which causes the rocket to move upward.
Newtons Laws of Motion Equations
1. Newton's First Law (Law of Inertia):
$\text{If } \mathbf{F_{net}} = 0, \text{ then } \mathbf{v = constant}$
$\mathbf{F_{net}}$: Net external force acting on the object
$\mathbf{v}$: Velocity of the object
2. Newton's Second Law (F = ma):
$\mathbf{F = ma}$
$\mathbf{F}$: Net force acting on the object (in Newtons, N)
$\mathbf{m}$: Mass of the object (in kilograms, kg)
$\mathbf{a}$: Acceleration of the object (in meters per second squared, m/s²)
3. Newton's Third Law (Action and Reaction):
$\mathbf{F_{12} = -F_{21}}$
$\mathbf{F_{12}}$: Force exerted by object 1 on object 2
$\mathbf{F_{21}}$: Force exerted by object 2 on object 1
Additional Equations:
Equations of Motion (from Second Law):
v=u+at
v: Final velocity of the object
u: Initial velocity of the object
a: Acceleration of the object
t: Time taken
$s = ut + \frac{1}{2}at^2$
s: Displacement of the object
u: Initial velocity
a: Acceleration
t: Time taken
$v^2 = u^2 + 2as$
v: Final velocity
u: Initial velocity
a: Acceleration
s: Displacement
Newton Laws of Motions Numericals
Numerical 1: Newton’s First Law (Law of Inertia)
Question: A car is moving at a constant speed of 20 m/s. If the brakes are applied, causing the car to stop in 5 seconds, calculate the acceleration of the car.
Solution:
Initial speed, $u = 20 \, \text{m/s}$
Final speed, $v = 0 \, \text{m/s}$
Time, t=5 seconds
Using the equation of motion:
v=u+at
$0 = 20 + a \times 5$
$a = \dfrac{-20}{5} = -4 \, \text{m/s}^2$
The car’s acceleration is $-4 \, \text{m/s}^2$, where the negative sign indicates deceleration.
Numerical 2: Newton’s Second Law (F = ma)
Question: A 10 kg object is acted upon by a force of 50 N. Find the acceleration of the object.
Solution:
Mass, $m = 10 \, \text{kg}$
Force, $F = 50 \, \text{N}$
Using Newton’s Second Law:
F=ma
$50 = 10 \times a$
$a = \dfrac{50}{10} = 5 \, \text{m/s}^2$
The acceleration of the object is $5 \, \text{m/s}^2$.
Numerical 3: Newton’s Third Law (Action-Reaction)
Question: A person is standing on a boat. If the person jumps off the boat with a force of 30 N, what is the reaction force exerted on the boat?
Solution: According to Newton’s Third Law, for every action, there is an equal and opposite reaction.
Action force (person jumping) =$30 \, \text{N}$
Reaction force (boat's movement) = $30 \, \text{N}$ in the opposite direction.
Thus, the boat will move backwards with a force of $30 \, \text{N}$.
Applications of Newton's Laws
Seat belts stop passengers from continuing to move forward when the car suddenly stops.
The force used in sports (like kicking a ball or throwing a shot put) depends on the mass of the object and how fast it needs to accelerate.
Rockets move upwards by pushing gases downwards with an equal and opposite force.
When you push your foot back on the ground, the ground pushes you forward.
When you push down on the ground to jump, the ground pushes you upwards with the same force.
Conclusion
Newton's Laws of Motion are fundamental principles that explain how objects move and interact with forces. The First Law shows that objects resist changes in motion, the Second Law connects force, mass, and acceleration, and the Third Law highlights the action-reaction pairs in every force interaction. These laws not only help us understand everyday movements but also form the basis for engineering, technology, and space exploration. By mastering these laws, we can better understand the physical world and the forces that drive it.
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FAQs on Newton’s Laws of Motion: Three Laws of Motion Explanation with Examples
1. Why do objects slow down?
Before Newton and Galileo, it was believed that the slowing down of objects was a natural tendency of the objects. Forces like friction and gravity were not known at that time. The frictional force opposes the motion of an object, causing it to lose energy resulting in slowing it down.
For instance, when we see a toy car moving on a concrete surface, the car’s speed is determined by the force of friction between the road and the car wheels. When the toy car is driven over a smooth surface, the wheel will meet with little resistance. This will set up a frictional obstacle and will let the car drive faster over all the plain tile surfaces.
This is very much unlike when a car toy is moving on an unsound surface containing gravel. Newton's first law of motion gives this concept of change in the state of rest or state of motion.
2. What does net force mean?
The net force ΣF is the vector sum of all the forces that are acting on a body at the same time. Adding the vector quantities is different from simple addition, as it involves direction in an account.
Let us consider that an object is subjected to two different forces of 30 N in the right direction and 20 N in the left direction, respectively, as per the diagram. Since the force acting on the right side is more, so the net force will be
3. Where do we apply Newton’s laws of motion in real life?
Newton’s law of motion is three physical laws that establish the science of kinematics. These laws define the relationship between the motion of the object and the force applied to it. Newton used these to explain many physical phenomena in addition to explaining Kepler's laws of planetary motion thus making them the most important physics laws.
a. First Law of Motion- An object at rest will stay at rest and an object in motion will stay in motion unless acted on by an external force. This means that the motion can neither change nor decrease without the effect of an unbalanced force. If a resultant force (the vector sum of the forces acting on the body) is zero, the velocity of the object is constant as well as both the magnitude and direction. For example, to prevent an accident, the car airbag inflates and prevents the driver’s head from hitting the windshield. We also include Inertia referred to as ‘The amount of resistance of an object or the direction of motion, including the speed and direction of motion. For example, when a stationary bus starts moving, then the passenger falls back and then jerks forward.
b. Second Law of Motion- If a force affects an object, the object gains acceleration, proportional to its strength and inversely proportional to its mass. For example, when we try to move an object including pushing or stopping it. One of the best examples is reducing the weight of racing cars, lowering the mass of the car will lead to an increase in acceleration and the higher the acceleration, the greater will be the chances of winning the race.
c. Third Law of Motion- For every action, there is an equal or opposite reaction. For example, when a person swims, he pushes the water backwards while the water propels him forward. Even helicopters create a lifting power by pushing the air down, leading to an upward reaction force. While designing rockets, the rush of gases from the rocket causes an increase in speed during ignition.
4. What are the best physics books on Newton’s laws of motion that students can follow for IIT and NEET?
Students preparing for competitive exams, like IIT and NEET, shoulder a huge responsibility to get a good rank and eventually grab a seat in the best engineering, technical or medical colleges in India. For this, the aspiring students must be very strong with their basic concepts of difficult and complex topics as questions are asked mainly in Multiple choice format. Hence, the fundamentals of the Science subjects must first be dealt with through NCERTs. The NCERTs are the best books, to begin with, which will help the students strengthen their hold over the subtopics using examples, illustrations and question banks given after every chapter. Vedantu has created study materials related to the NCERTs including short notes and other resources which students can refer to during the learning process. Other reference books are:
NEET- The Concept of Physics by HC Verma (providing detailed presentation of physics-based concepts and exhaustive list of Question banks through Multiple Choice Questions) and COncepts of Competition Physics for CBSE PMT by Agarwal (considered to be the best for pre-medical tests which have different types and difficulty levels of questions distributed as per the requirement of the medical exams).
IIT-JEE- Books by HC Verma where examples and question banks are relatable. Volume 1 covers topics of std 11 and Volume 2 covers topics of std 12. Books by DC Pandey contain more objective and subjective based questions and are very well-explained for advanced learning.
5. How should students prepare for Newton’s law of motion using sample papers?
For Science students, it is especially mandatory to prepare for difficult school-based and college-based competitive exams like IIT-JEE, NEET, etc., by solving as many sample papers as possible. All the sample papers curated by the experts of Vedantu are updated as per the latest syllabus by CBSE and uploaded to the website on a timely basis and can be downloaded easily in PDF format for free. Although practising many sample papers and Previous Years’ Question papers might be very tiring, it makes the student fully prepared to fight the tough battle by helping them master the subject. More than the set of exercises with numerals given after every chapter, students should also focus on the ones provided in the sample papers to clear concepts and build a stronger foundation of the topic.
6. What are the key Newton's Laws Of Motion Examples?
Some Newtons Laws Of Motion Examples include:
A car's airbags inflate upon a crash due to the First Law of Motion.
The acceleration of a racing car is affected by its mass, as described by the Second Law of Motion.
The propulsion of a rocket is explained by the Third Law, where the rocket’s expulsion of gases results in an opposite force pushing the rocket upwards.
7. How are Newton's Laws Of Motion In Our Daily Life Applied?
Newton's Laws can be seen in everyday activities:
First Law: Seatbelts in cars prevent passengers from continuing to move forward during a sudden stop.
Second Law: The acceleration of a car depends on its mass and the force applied.
Third Law: When a swimmer pushes the water backwards, it moves forward due to the reaction force.
8. How do Physics Newton's Laws Of Motion apply to sports?
In sports, Physics Newton's Laws Of Motion help explain how forces act on objects like balls, players, and equipment. For example:
First Law: A soccer ball will stay at rest unless kicked.
Second Law: The harder you kick a ball, the faster it accelerates, as force and acceleration are related.
Third Law: When a person jumps, they push down on the ground, and the ground pushes them upward with an equal force.
9. Can Newton’s Laws of Motion explain the movement of celestial bodies?
Yes, Newton's First Law explains why planets continue their orbit unless acted on by another force (like gravity). The Second Law helps us understand how the mass of a planet affects its movement under the influence of a force. Finally, the Third Law explains the interaction between celestial bodies, such as the Earth and the Moon, where the forces exerted on each other are equal and opposite.
10. What equations can help in solving problems related to Newton's Laws of Motion?
The Newton Laws Of Motion Equations are:
First Law: $\mathbf{F_{net}} = 0$ implies that an object in motion will continue moving at a constant velocity unless acted on by an external force.
Second Law: F=ma, where F is the force, m is the mass, and a is the acceleration.
Third Law: $\mathbf{F_{12} = -F_{21}}$, indicating that the force exerted on one object is equal in magnitude and opposite in direction to the force exerted on the other object.
11. Where can I download Newton's Laws Of Motion PDF for easy studying?
You can download a FREE PDF on Newton’s Laws of Motion from Vedantu. These PDFs contain explanations, examples, and practice problems to help students understand the laws in detail and apply them to various scenarios.
12. How do Newton's Laws of Motion affect our understanding of physics?
Newton’s Laws are fundamental in understanding how objects move and interact with forces. These laws are the foundation of classical mechanics, providing insights into the motion of objects on Earth and in space.
13. How does Newton's Third Law explain rocket propulsion?
According to Newton’s Third Law, when a rocket expels gas downwards, the equal and opposite reaction forces push the rocket upwards, allowing it to launch into space.
14. What are some real-world examples of Newton's Laws of Motion in action?
Newton’s laws are seen in various real-world applications, such as:
First Law: A book on a table remains at rest until moved by a force.
Second Law: It takes more force to accelerate a heavier vehicle.
Third Law: Walking, swimming, or using a jet ski all involve action-reaction forces.
