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Newton's Laws of Motion

Last updated date: 09th Apr 2024
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About Newton's Laws of Motion

Newton's laws of motion give a scientific relationship between the forces that act on a body and the changes that occur due to this force. Sir Isaac Newton formulated the laws of motion in the year 1686 in his book ‘Principia Mathematica Philosophiae Naturalis’.

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What are the Three Laws of Motion?

The Three Laws of Motion are:

  1. Newton’s first law - 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. 

  2. Newton’s second law - 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.

  3. Newton’s third law - According to Newton's third law of motion, to every action, there is always an equal and opposite reaction.

First Law of Motion

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 generalized 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

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 or 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

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.

Some of Newton’s Laws Examples are Mentioned Below

  1. You apply force when you want to move your study table from one side of the room to another side.

  2. A cargo train is running on the track at 60 kilometres per hour.

  3. Swimming in the water with an almost constant velocity.

Isaac Newton was a scientist from England. He was a bit stuffy with unpleasant hair, but he was a brilliant person. Newton is the founder of differential calculus and has dedicated his life to the world of physics. One of his significant works is the laws that govern classical physics. His ideas and concepts have been experimentally verified throughout the years. These are called Newton's Laws of Motion.

FAQs on Newton's Laws of Motion

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 given by

Σ F = 30N- 20N

Σ N = 10 N in the right

If there are multiple numbers of forces acting on an object, then Newton's second law of motion is given by

\[\overline{a}\] =    \[\sum \frac{\overline{f}}{m}\]

This is a universal formula for force, and it shows that the direction of acceleration is in the same direction as the net force.

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 Questions 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 numerical given after every chapter, students should also focus on the ones provided in the sample papers for clearing concepts and building a stronger foundation of the topic.