Sir Isaac Newton

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

• Birth: 16th January 1643

• Nationality: English

• Professions: Physicist and Mathematician

• Newton was one of the most important thinkers during the scientific revolution.

The most important theories laid down by Newton were his three laws of motion, known as Newton's Laws of Motion. Though considered basic today, these laws were revolutionary centuries ago. They describe what happens to an object when it is at rest, in motion, or when forces act upon it.

Newton's First Law of Motion

The first law states that an object cannot move, stop, or change direction without an external force being applied.

• The property of objects to resist changes in their state is called inertia.

• Another name for Newton's first law is the law of inertia..

• A body will remain at rest or continue in motion at constant velocity unless acted upon by a net external force.

• If the object's velocity is zero, it remains at rest.

Newton's Second Law of Motion

Newton's second law explains that the force on an object is proportional to the product of its mass and acceleration:

F=maF = maF=ma

• The momentum of an object changes at a rate proportional to the net force applied, and this change occurs in the direction of the force

• Larger forces cause larger changes in momentum.

Examples:

1. A car of mass 65 kg accelerates at 5 m/s⊃2;:

F=65×5=325 NF = 65 \times 5 = 325\,NF=65×5=325N

2. A lorry of mass 165 kg accelerates at 6 m/s⊃2;:

F=165×6=990 NF = 165 \times 6 = 990\,NF=165×6=990N

3. A bike of mass 12 kg increases its velocity from 5 m/s to 10 m/s in 5 seconds:

F=12×10−55=12 NF = 12 \times \frac{10-5}{5} = 12\,NF=12×510−5​=12N

Newton's Third Law of Motion

The third law is one of the most important laws of physics:

• Every action has an equal and opposite reaction.

• When two objects interact, they exert forces of equal magnitude but in opposite directions.

Examples:

1. A bottle of milk resting on a table:

   • The bottle exerts a downward force on the table.

   • The table applies an upward force of equal magnitude, also called the reaction force, normal force, or contact force.

2. A cat sitting on a chair:

   • The cat exerts a downward force on the chair.

   • The chair applies an upward force of similar magnitude.