Newton's First Law of Motion

In his study about motion, Isaac Newton formulated the Newton's Three Laws of Motion. The first law states that

"An object at rest will remain at rest and an object in motion will continue in motion unless acted upon by an unbalanced force." 

When an object is at rest, it will continue to be in rest position. When a nonzero force acted on that object, there's a certain little amount of time that it will not move immediately upon the application of the force. On the other hand, a moving object has a tendency to continue moving even if a force is applied to make it stop. This tendency of a body to resist a change in its state of motion is called inertia. The first law of motion explains that a body can resist a change in its state of motion. For this reason, the first law is also called as the Law of Inertia.

Inertia can be classified into three - inertia of rest, inertia of direction and inertia in motion.

Suppose you are sitting at the backseat of a car. As the car starts to move forward, you tend to move backward on your seat, this is because of the inertia of rest. Your body continue to be at rest state and opposes the motion of the car, that's why instead of moving forward as in the direction of the moving car, your body tend to remain at rest in the seat causing the backward motion.

As the car turns left, the body's direction is moving to the right and as the car turns right, the body moves left. This tendency of the body to resist a change in its direction is called inertia of direction.

While the car is moving forward, the body is in motion same as the direction of the car. During a sudden stop, the body moves forward instead of stopping. This is because of the inertia of motion. A body has a tendency to continue moving even if it is forced to stop.

The following situations can help us understand more about the law and find out how this concept is applied to real-life situations.

Situation 1.

Ritz is driving his car faster than the speed limit. Assuming he is not wearing a seatbelt, is he safe? What might happen if he comes into a sudden stop?


While driving, Ritz's body is in motion in the direction of the car. When the car comes to a sudden stop, he might fly off the car since his body has a tendency to continue moving forward even if the car stopped. Thus, driving or riding a car without wearing seatbelt is not safe. Seatbelt is our protection and help us stay in place in our seats when the car stops.

Situation 2.

Imagine you are in a rollercoaster ride. Have you felt like blood rush up from your feet to the head everytime the rollercoaster is going down? Why is this so?


Inertia. Our body moves up and down as in the rollercoaster. Everytime it goes up, we go up. As it goes down, the body continues to move up giving us the feeling like our blood is moving up from our feet.

Situation 3.

Al is working in an appliance center. He has to deliver a refrigerator to a customer. The driver of the delivery truck is asking him to stay at the back of the truck to hold the refrigerator for there's no rope available to tie it up. Will he still continue to deliver the refrigerator in this situation?


Definitely, no. As the truck moves, the ref and the person is also moving, When the truck changes direction, the ref moves in an opposite direction of the truck. When the truck stops, the two continue to move forward. Knowing that the refrigerator is heavier, it is hard to hold it up in place. Thus, riding at the back of a truck with a refrigerator untied is not safe. It can cause injury to the person and the ref might also be destroyed.