What are Newton’s Laws of Motion?

Whatever one observes today comes under the purview of the laws of motion. For example, when an object is kept at rest, when it is in motion when it is trying to come in motion. Even the earth and the other planets are made up of rocks. But it keeps revolving around the sun although there is no one to push it or pull it. Still, there is some force acting and it is called gravitational force. Such thoughts might arise in your mind. Let us see how it impacted Isaac Newton to state the first law, second law, and the third law.

Who is Sir Isaac Newton?

Sir Isaac Newton was an English scientist who worked and developed Calculus and physics. Although many other scientists like Aristotle and Galileo had already proposed the laws of motion and force, Newton’s first law, second law and third law are found to be more scientific.

Laws of Motion

 In our daily life we are observing so many things which keep motivating us to think about how things work around us. Have you seen the tall and beautiful mountains? For how many years have they been staying in the same place without moving? What makes it not to move? These mountains are made up of huge and small rocks and they are not easily moveable. But the small rocks and sand particles which we see around are easy to move. But it cannot move unless someone or something causes it to move. The mass of the object matters along with the force applied to the object.

Even the earth and the other planets are made up of rocks. But it keeps revolving around the sun although there is no one to push it or pull it. Still, there is some force acting and it is called gravitational force. Such thoughts might arise in your mind. Let us see how it impacted Isaac Newton to state the first law, second law and the third law.

How did Isaac Newton discover the laws of motion?

Imagine you are standing under an apple tree playing with your friends and suddenly an apple hits your head. Will you take time to think why objects do not go up and why it falls? It is said that this made Newton think about laws of motion. There are three laws of motion Newton has discovered. They are the first law, second law and the third law. It is written in the book Philosophiae Naturalis Principia. It is interesting to note that the universe obeys these laws.

Newton’s first law of motion

Suppose there is an object like a ball or pen in front of you and it is staying at rest. It will stay in the same position until you do something to it and make the object exert some force. This is what newton’s first law of motion says. It is also called as law of Inertia. But if you throw any object like a ball up in the sky, it exerts some force. The ball will keep going up until some external force stops it. The ball’s velocity moves it upward. But it slowly comes downwards and the velocity decreases. It is because of the earth’s gravitational force that pulls the object down to the ground. As the ball rolls in the ground its speed gets slower due to friction and then it stops. The friction force acts in a direction that is opposite to the motion of the ball.

As per this law any body continues its state of motion or rest unless an external force is applied.

Now let us think of some other scenario. Have you seen the video footage of the astronauts in space? It looks like they are floating in the spaceship. When they throw an object at some speed it keeps moving in the same direction unless it hits an object. It would not fall as it falls in the earth since there is no gravity in space.

Net force 

There is a force that acts in the same direction as the motion of any object. It is called a parallel force. Now, in this object, two or more forces are acting. Instead of seeing it separately, they can be combined. This is called the net force.

If the force is acting in the direction opposite to the motion of any object, the net force will be the difference of one force from the other. This force causes the ball to stop as we saw earlier.

These forces can be of equal or unequal magnitude. If two forces are equal and acting in opposite directions, the net external force is zero. But if the forces are unequal, the net force is the difference of the lesser force from the greater force.

Newton’s first law of motion examples

While driving in a car if the driver takes a sharp turn everyone will lean sideways. This is because you are continuing to go in one direction and suddenly an external force is applied and the direction is changed. This is an example of inertia. What are the examples of Newton’s 1^st law of motion you can give?

Newton’s second law of motion

As per this law the rate of change of momentum of an object is proportional to the force applied. Mathematically this can be expressed as

Where p is the momentum, t is the time, F is the force, m is the mass and a is the acceleration of the object.

Suppose that there are two round shaped objects of same size on the ground. One is a football and the other is a metal ball. If you kick the football with some force, it will move forward. But with the same force if you kick the metal ball, it will not move far like the football. It is because of the two different masses of the object. The mass of football is very less than the metal ball. 

Now, imagine there are two footballs of the same mass. If you kick the first object with less force and the other with greater force, which one will go far? The ball kicked with greater force will go far. It is because of the acceleration. When you apply more force to an object, the acceleration is also more. Thus, force is the product of the mass of an object and acceleration. It has both direction and distance. So, it is a vector quantity.

Second law of motion examples

Suppose that you are pushing an object along with your friend. You will be able to move the object faster than pushing it alone by yourself. It is because the force is more when you move with your friend. So the acceleration is also more. 

When you are riding a bicycle the speed is more if you push the pedals faster. You can reach a longer distance at a shorter time. But if add so much weight to the bicycle’s basket and pedal it with the same force, the bicycle moves comparatively slower than the above case.

Newton’s third law of motion

According to this an equal and opposite reaction is present for every action. Both the action-reaction occur on two different objects. If you see someone swimming in the water, you might have noticed the person pushing the water backward for the person to move forward. In the same way, when a person fires a bullet, the bullet goes forward. But the gun moves backward at the same time. There is an opposite reaction to these actions. This is exactly the third law of motion by Newton. These are the third law of motion examples.

 Context and Applications   

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for 

• Bachelors in Science (Physics) 
• Masters in Science (Physics)