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# Newton’s Laws of Motion : Definition & Examples

Jul 15, 2022

## Newton’s Laws of Motion – Overview

Newton’s three laws of motion explain the motion between massive bodies and their way of interacting with each other. Newton’s laws of motion seem simple for today’s generation, but in the past three centuries, these laws of motion have been revolutionary for humankind.

Newton has always been categorised as one of history’s most important scientists. His theories served as the foundation for modern physics. He expanded on notions set forward in the writings of earlier scientists, such as Aristotle and Galileo, and was able to substantiate some of these theories. He was an expert in astronomy, maths, and optics; he created calculus. (In almost the same period, the German mathematician Gottfried Leibniz also was attributed for independently creating it.)

The work of Newton in analysing gravitation and planetary motion is undoubtedly the best recognised. Newton formalised the synopsis of how massive bodies start moving under externally applied forces in his seminal work, “Philosophiae Naturalis Principia Mathematica” (Mathematical Principles of Natural Philosophy). Newton formulated his theory after being prompted by astronomer Edmond Halley, who admitted that he had dropped his evidence of elliptical orbits a few years earlier.

## Newton’s Law of Motion

Newton’s consideration of enormous bodies was made simpler when he formulated his three scientific laws of motion by treating them as mathematical observations without rotation or size. It enabled him to focus on occurrences that can only be explained in terms of length, mass, and time while ignoring considerations like temperature, friction, material properties, air resistance etc. As a result, Newton’s three laws of motion cannot be utilised to describe the behaviour of big rigid or flexible objects properly. Still, they frequently offer appropriately accurate predictions.

Newton himself rarely defines such a reference frame. Still, his equations apply to the motion of large masses in an inertial frame of reference, often known as a Newtonian reference frame. Now, what is an inertial reference frame? It is a 3-dimensional coordinate system that is either fixed or moving uniformly in one direction, i.e., not rotating or accelerating. Newton found his laws of motion could adequately capture motion with such an inertial reference frame.

### Newton’s First Law of Motion

According to Newton’s first law of motion, an object or a body will stay at its resting position. Similarly, an object or a body will continue to be in motion unless an external force is applied to that object or body. It simply means that nothing can begin, end, or alter course on its own. Some external force must be acting on them. Inertia is occasionally used to describe a huge body’s ability to resist changes in its state of motion.

 Examples of Newton’s First Law of Motion A paper holder resting on the table  In this case, a normal force from the table distributes the weight of the paper holder when it is resting on it, maintaining it in equilibrium. Unless an extra external force is used to move it, it will stay in its equilibrium position. A bicycle rides down a level route at 20 kilometres per hour. When a biker is riding ahead at a steady pace, forces pushing against him are balanced by pushing him backward. The biker is aligned and will keep moving in the same direction and at the same pace until an external force acts upon him. The bicycle slows down due to external influences like air resistance and friction. A rocket in outer space A rocket would not be subject to any external forces in outer space because there is no air pressure and hardly any gravity pull. As a result, it would continue to move in one direction and at the same speed without consuming fuel. An automobile abruptly slows down. When an automobile suddenly decelerates, things keep travelling in the same direction and at the same speed until a force is applied. Until the restrictive force of their seatbelts limits their mobility, passengers continue to go “forward.” Unless other external forces impact them to cease their motion, loose objects or bodies in the vehicle will continue to travel ahead.

### Newton’s Second Law of Motion

Newton’s second law of motion states what happens to a large body or object when subjected to an external force. The law states, “The external force applying on a body or object is equal to that object’s mass times its acceleration (velocity)”. The formula for Newton’s second law of motion is

F = ma,

where

F = External force

m = Mass of the object

a = Acceleration or velocity

Both acceleration and external force are vector quantities, which ultimately means they have both a direction and a magnitude. The force may be a unified force or the vector sum of multiple forces, representing the net force due to adding up all the forces.

Thus, students can conclude that an object or body will travel in the force’s direction when subjected to an external force. Acceleration is inversely related to mass and directly to the external force acting on the object.

 I.e. a ∝ F and a ∝ 1/m from which F = ma

With the help of Newton’s second law of motion, students can better understand why an item could slow down, speed up, or change its direction when an external force is applied to it. The law also explains why it is more challenging to accelerate a heavy item and to bring it to a stop.

### Newton’s Third Law of Motion

Newton’s third law of motion states, “There will always be an equal and opposite reaction to every action.” This law explains what transpires when one body applies force to some other body. In Newton’s third law of motion, when two objects or bodies push against each other, the second object pushes back with equal force because forces always occur in sets.

For instance, if a person pushes a bicycle, the bicycle will also apply pressure against the person. In the same way, if a person takes out water from the well with the help of a rope, the rope will pull back against the person. Thus, Newton’s third law of motion states that if gravity pulls an object down to the earth’s surface area, the earth pushes up against one’s feet.

 Examples of Newton’s Third Law of Motion A spaceship ignites its engines to travel to a high elevation Action: The engines propel a stream of heated gases downward (i.e. the hot gases act as a force). Reaction: Hot gases push the spaceship upward in response (i.e. the external force acts on the spaceship). Motion: The reaction force from heated gases is the only external force acting on the spaceship, causing the object to speed upward. The Moon and the Earth Action: The earth attracts the moon. Reaction: The moon exerts an equal and opposite reaction force on earth. Motion: The moon rotates around the earth in a circular path because only one pressure is exerted on it.

#### Conclusion

Newton’s three laws of motion continue to be frequently applied even today to describe the types of acceleration and objects that one experiences daily despite having been supported by innumerable studies over the previous three centuries. Studying substantial bodies that are bigger than the micro-scale discussed by quantum theory and travelling at lower velocities than the extremely high velocities discussed by relativistic physics is recognised as classical mechanics, and these concepts serve as its foundation.

1. Andrew places his folder on the passenger seat while commuting to work, and by the time he arrives at his destination, he sees it was dropped on the front seat floor. He wants you to explain the mechanics behind this case and why this occurred. What can you say about this?

Ans. Andrew may understand this by using Newton’s first law of motion. The folder moves ahead with the car due to the law of inertia and drops on the front seat floor. The folder will remain in motion unless an additional external force is applied to the object.

2. Which of Newton’s principles most accurately explains how a magician may remove a tablecloth from behind serving ware?

Ans. Newton’s first law of motion can explain the tablecloth being pulled under the dishes by a magician. During the technique, a tiny lateral force is exerted. Following Newton’s first law of motion, which keeps them undisturbed, the plates and glasses remain resting. In the technique, the tablecloth is so frictionless that it doesn’t cause any resistance to the glasses and plates.

3. Describe the law of inertia concept.

Ans. Unless operated upon by an external stimulus, Newton’s first law of motion describes that “A body at rest will stay at rest and a body in motion will stay in motion in the same direction and at the same speed.” Things have a propensity to “continue whatever they’re performing.” Objects have a built-in tendency to avoid alterations in their rate of motion. Inertia is the tendency for objects to resist alteration in their state of motion.

Thus, the law of inertia can be defined as the reluctance of a body towards change in its state of motion.

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