**Sir Isaac Newton**

Sir Isaac Newton discovered the reason for an apple falling from a tree which was gravity, therefore, inventing the laws of gravity. He was one of the most successful and brilliant physicists to have ever existed. He made very important theories and made the world believe that the universe obeyed his theories.

He was born on the 16th of January in the year 1643. He was an English physicist. He was also a mathematician. In the scientific revolution, Newton was one of the most important thinkers.

The most important theories laid down by Sir Isaac Newton were his three laws about motion. These theories are called Newton'sNewton's laws of motion.

The laws laid by newton are considered very basic today, but they were considered revolutionary about centuries ago. The law tells us what happens to an element when it is still or in motion or when different types of forces act on it.

**Newton's first law of motion**

The law states that an object cannot move, stop, or change direction without a force being applied to the object. The force must come from the outside. The property of different types of elements to resist changes in their state is called inertia. Newtons'Newtons' first law of motion is sometimes called the law of inertia.

Newton'sNewton's first law states that a body will continue to be at rest or it will continue to be in motion unless a net external force starts to act on it.

The object will continue to move at constant velocity if no unbalanced force is acting on it. If the object's velocity is zero, then it will not move, and therefore it will continue to be at rest.

**Newton's second law of motion**

The second law of motion by newton tells us that the force is proportional to the product of mass and acceleration when an external net force starts to act on an object.

Newton'sNewton's second law states the rate of change of momentum of an element is directly proportional to the resultant or net force acting on the element in the direction of the resultant or net force.

The larger the force, the larger the momentum change rate. The momentum change rate takes place in the direction of the force.

From the law, F = mv-mu/t => m(v-u)/t => ma

Therefore, f = ma

When a force of magnitude 1N acts on an object of mass 1 kg, the object produces an acceleration of 1 m/s^2.

A car of mass 65 kg is accelerating at 5 m/s^2. What is the net force on the car?

- Putting it into the equation, f = 65 x 5 = 325N.

A lorry of mass 165 kg is accelerating at 6 m/s^2. What is the net force on the car?

- Putting it into the equation, f = 165 x 6 = 990N.

A bike of mass 12kg increases its velocity from 5 m/s to a velocity of 10 m/s in a time of 5 seconds. What is the net force on the biker?

- Putting it into the equation, f = 12 x (10-5/5) = 12N.

**Newton'sNewton's third law of motion**

The third law of newton is one of the most important laws of physics. This law tells us what happens when one element exerts a force on a different or the same element.

Newton'sNewton's third law states every action has an equal and opposite reaction.

When two objects meet, they exert forces on one another. The forces are opposite in direction but of the same magnitude.

Let'sLet's look at some examples in order to fully understand Newton'sNewton's third law.

Consider a bottle of milk resting on a table. The bottle of milk exerts a downward force on the table, and therefore the table applies an upward force of equal magnitude on the bottle of milk. The upward force that the table exerts on the bottle of milk is also called the reaction force, normal force, or contact force.

Suppose a cat is sitting in a chair. The cat exerts a downward force on the chair. As a result, the chair applies an upward force of a similar magnitude as the downward force on the cat.