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Newton's First Law of Motion


Sir Isaac Newton was a well known mathematician as well as a physicist who plays an important role in the revolution of science field especially in physics.He wrote a book named Philosophiee Naturalis Principia Mathematica and published in 1687. Newton's laws of motion are the important physical laws which built a foundation in classical mechanics.The details of the first law is given below.

Issac Newton
Sir Isaac Newton

What is Newton's First Law of Motion?

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The first law of motion states that, every objects continue its state of uniform motion or rest until and otherwise an external force is acted upon it.This law is also known as law of inertia. This law means that, there is a natural tendency of objects to do continuously what they are doing. All body rejects the changes in their present states, whether it is rest or in motion. The given figure illustrate the first law of motion. Actually, this law is a definition of force. And it tells that when a body is acted upon an external or an unbalanced force, it will accelerate. Otherwise it continue its present state.
This law provides a definition of force. A force is any influence that can change the velocity of an object. To accelerate something a net force is required.
Newton's First Law

Newton's First Law Formula

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According to the first law, the velocity of an object is constant unless it is acted upon by an unbalanced force. so, if the force is zero, the velocity remains constant or acceleration will be zero. Hence, the mathematical representation of the Newton's first law is given by,

if $\sum$ F = 0
or $\frac{dv}{dt}$ = 0

Newton's First Law of Motion Examples

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Some of the examples of Newton's first law is given below:
  • While skating, we fly forward when the skateboard is hitting a rock that stops the motion of the board.
  • The rapid flow of blood from head to your feet while quickly stopping when riding on a descending elevator.
  • Seat belts safely provide an unbalanced force that can stop or slow down our body when the car stops or slows down.
  • Air bags work by increasing the time of impact and decreasing the force of impact thus stopping you from getting hurt and being killed.
  • Headrests are placed in cars to prevent injuries while the sudden break occurs.

Newton's First Law Experiments

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  1. Ball Bounce Experiment

The material required for this experiment:

  • A basket ball
  • A cricket ball


1) First bounce a basket ball and a cricket ball to compare their level of bounces. And begin from around the 1m height.
2) When we put the cricket ball on top of the bigger one and then drop it. What change will happen to the bounce of the two balls?
The energy of basket ball is transferred in to the cricket ball while motion. If we look at the larger ball, compared to the smaller one the level of bounce is less.

2. Penny on a Card Experiment

The materials required for this experiment:

  • A small beaker
  • A card
  • A coin


1) Keep a card on the top of a beaker.
2) And placed a coin on the card.
3) Suddenly pull the card towards you.
4) The coin will drop in to the beaker.

Every object has inertia. So the coin which is placed on the top of the card is also posses inertia. If we move the card slowly, the coin also move with the card. If you move it quickly, the coin stays in one position and then drops in to the beaker.

Newton's First Law Problems

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Some of the problems related to the first law of motion is given below:

Solved Examples

Question 1: Newton's first law of motion is also known as law of inertia. Justify your answer.

Newton's first law tells that a particle originally at rest, or moving in a straight line at constant velocity, will remain in this state if the resultant force is acting on it is zero. And the inertia is the tendency of an object to resist the changes in motion. So, both the concept is same. Hence the first law of motion is known as law of inertia.


Question 2: If the forces acting on a body are balanced, then the body
a) must be moving with a velocity
b) must be accelerating
c) must not be accelerating
d) none of these

c) must not be accelerating


Question 3: Which of the following condition is possible according to the Newton's first law?
1) An object moves at constant velocity under the action of a single force.
2) Two forces act on a body and the body moves at a constant velocity in a straight line.
3) A car drives along a straight road at constant velocity under a net force.
4) An object accelerates without exerting forces on any other bodies.

1) Not possible
2) Possible
3) Not possible
4) Not possible