Newton’s First (1st) Law of Motion (Law of Inertia)

The laws of the motion explain the relationship or connection between the body and forces acting upon it and the motion in response to those forces formulated by the English physicist and mathematician Isaac Newton. So here in this article, we have made you understand Newton’s First Law for Kids in the simplest way.

Newton’s First Law Definition

According to Newton’s first law of motion, ‘’every object or body will always remain at rest or in uniform position until and unless an external force is applied to it. ‘’

Newton’s First Law of Motion

Let us understand some terms for easy understanding of Newton’s first law for kids:

Force: A force is a push or pulls applied to one object by some other object. The unit of the force is considered as newtons or simply you can write N.

One Newton (standard metric unit of force) can be referred to as the amount of force which is needed by a mass of 1 kg to produce an acceleration of 1 m/s

Thus, 1 Newton = 1 kg m/s2

External force: An external force can be defined as a force exerted on the object from outside rather than internally. For example, the force of the gravity exerted by the earth on the moon is an external force on the moon.

Net force: Net force is generally denoted as E F is the total force exerted on the object. If at a point many forces are applied on the object then sum total of all the forces is referred to as the net force.

Unbalanced force: Unbalanced forces are those forces that produce a change in the motion of an object.

Balanced force: Balanced forces are those forces that are same in size but different or opposite in direction.

Friction: Friction can be understood as the resisting power of one object to the motion of another.

There are two parts explained in the above definition. The one that understands the behavior of the stationary objects and the other that understand the behavior of the moving objects. This implies that if the objects are at rest then the velocity tends to be 0m/s whereas if the objects are in moving position then their velocity is not equal to 0m/s. The objects have the ability or behavior to do what they are doing. If an object is in a position of rest it tends to remain in rest. If an object is moving with a velocity of 2m/s then it will remain moving with 2m/s velocity. If it moves with the velocity of 7m/s then it will move with same velocity 7m/s. The same motion of the object is maintained same until any unbalanced force will not be exerted on it.

This law is normally understood as the name of the law of inertia. The tendency of many objects or bodies to resist a change in motion is what known as inertia. The law of inertia has been firstly discovered by the Galileo Galilee for horizontal notion on earth. There is a direct opposite of Newton’s law of inertia to more known origins of motion. The thought that struck in Newton’s mind is that the objects have the tendency to maintain a position of rest. An object in the moving position will also comes at rest after a period of time until any force is applied on it in order to keep it moving. But if nothing will be doing then the object will definitely attain a position of rest and will stay in the rest. Therefore, it is an idea that rules in the Newton’s mind that it is the natural ability of an object to stay in the position of rest.

Experiment by Galileo: In an experiment, using a pair of slanted planes confronting each other. He found that a ball firstly rolls down of one plane and rolls up on another plane approximately up to same height. Also he found out that if smoother planes were to be used then the ball will be rolled up closer to the original height from the opposite plane. The main theme observed by Galileo behind this is that the only difference between the original and final height is due to fiction persisting. So he concluded that if that fiction would be completely removed then the balls will attain same height.

Galileo additionally found that paying little heed to the edge at which the planes were situated, the final height was almost equal to the original height. If the slope of the oppositely inclined plane was decreased then the ball would roll a more distance so that it can reach to the original height.

Also, if the inclined plane were put at an angle of 0 degrees then the ball would make complete action to reach at the original height. But if the oppositely inclined plan was not at all inclined then the ball would continue in the motion itself.

The law means that there is no net force that is acting on the object or body (all the external means are cancel out each other), thus the body will be maintaining a constant velocity. Velocity is defined as a vector quantity which defines both the speed of the object and the direction of its motion. So if the velocity will be at 0 then the object will be at rest. Again, if an external force will be applied on the object than the velocity will change corresponding to that force.

This law can also be called uniform motion. An object can do whatever it wants unless an external force is exerted upon it. If it is in the position of rest then it will remain at rest. If it is in the moving position then it will continue to move without changing its speed.

The Newton’s first law for kids can be explained by these points:

  • The net force acting upon a body will be zero if the body is at rest.
  • The net force acting upon a body is zero if the body is moving in uniform motion and that in a straight line.
  • The net force acting upon the body will not be zero if the body is neither at rest nor in uniform motion.
  • The net force acting upon the body will not be zero if the body is in changing direction.

Newton’s First Law Formula

The law can be described mathematically as:

Ef =0 <-> dv/dt = 0

This E (sigma) sign depicts the vector sun of all the forces acting or the net force acting upon the object.

For example: A block is there on a smooth surface. By calling smooth surface we assume that there is no fiction acting upon the surface. The block is not moving, it is at rest.

Now our task is to evaluate the forces acting upon the block. There are two forces acting upon the block. One is the force of gravity applied and the other one if the force of the normally smooth surface. There is no force exerted on the block in the horizontal direction. So the forces acting upon the block in the vertical direction has equal magnitude, hence they cancel each other out, thus there is no force externally applied on it. It concludes that the block is at rest and this confirms the Newton’s first law of motion.

If we applied a constant force on the block then it will start moving in the direction of the exerted force with constant acceleration.

Application of Newton’s first law on our human body:

To broaden your concept we can also apply Newton’s 1st law of motion for kids on our own body. Have you at any point feels a lightheaded inclination after coming to a stop in a plunging lift? Better suggested to hold on the railing of the elevator.

Every component of our body moves down along with the movement of the lift. Suddenly when the elevator comes to a stop, the floor of the elevator exerted an external force to our body, producing it to come to a top.

Newton’s First Law Examples

Wearing a seat belt:  

Newton’s first law of motion has to be applied in the situation of seat belts. Have you wondered what happens when we don’t wear the seat belt and suddenly the vehicle stops? You move in forward direction and continue in motion until any unbalanced force acts upon you. As we have made you understood earlier that unbalanced force refers to a force that changes the motion of an object. So when you stop at a point you wouldn’t stop motion unless any force is caused to change your motion and put you at rest. Therefore if you will wear the seat belt then it would be acting as an unbalanced force and it prevents you from being in motion.

Sudden moving bus:

Have you ever come across while travelling in a bus that when bus suddenly starts after a stop at the station. The passengers travelling inside the bus tends to fall in reverse which means backwards. This is because the inertia of rest. When the bus all of a sudden starts then the lower part of our body comes in contact of the bus also moves as the bus moves but the upper part of the body remains in the rest position due to law of inertia. That’s why the passengers falls backward.

Winnowing on grains:

As you may know that by winnowing the grain got separated from the husk. It is an agricultural process in which we separate the grain and the husk. Grain has the larger mass as compared to the husk. Thus, the inertia of grain is always more than the inertia of husk. Thus more force has to be act in order to change its motion. When they fallen from height in gentle wind, because of the larger inertia they just fall down vertically. On the other hand the mass of husk is about negligible and thus have same inertia. Very little amount of force is required to change their motion. When fallen from height they get carried away in the direction of wind through some distance. Thus, the husk and grain get separated.

Drying of clothes by shaken:

It must be a very funny activity you do just for having fun. But it is really important to do. Your mothers must do it when drying the clothes. So when a cloth is shaken the water particles from the clothes come out. When the cloth is shaken for drying it tends to obtain motion. But due to inertia the water particles stays in the position of rest. Thus they get separated from the clothes and clothes can be dried.

Solve the worksheet:

Given are questions related to Newton’s first law of motion. Solve the given questions.

  1. Name the factor responsible for keeping an object at rest or maintaining an object’s constant velocity?
  2. Describe the relation between the inertia and the mass?
  3. Explain inertia in your own words?
  4. Calculate the amount of force to be applied by you on the ball in order to keep in moving if you were in a spaceship and fired a cannonball into space?
  5. There are two closed containers placed at the same table? One container is packed with lead and the other container is packed with few feathers. How will you evaluate which one has more mass?
  6. Explain that how much force will you exerted on an object to maintain its constant velocity if the force of friction acting upon the object is 100N?
  7. Evaluate net force applied on the crate?
  8. Determine the acceleration?
  9. How can we examine the weight of any astronaut which is far away from the planets?
  10. On what kind of path will the planets circulate if the force of the sun stops acting on them?
  11. Calculate the net force if you push a cart to the right with 10N of force and a friend pushes the cart to the left with 10N of force?

Final words

The deeper understanding of Newton’s first law of motions is essential for kids to get various terms of science in their day to day life. So please read the above information carefully.  Solve the worksheet provided. All the best.

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