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# 1.3: Newton's Law of Motion

TABLE OF
CONTENTS

### 1.3: Newton's Law of Motion

When we observe objects around us, one question that comes to mind is why they move or stay still. The answer to this question can be explained using Newton's laws of motion. These laws describe the fundamental principles of motion and the effects of forces on objects.

The first law of motion, also known as the law of inertia, states that an object at rest will stay at rest, and an object in motion will continue to move at a constant speed and direction unless acted upon by an external force. For example, when a sliding box slows down on its own, the net external force on the box is the friction force that acts against the box's motion to slow it down.

Newton's first law considers bodies at rest or in motion at a constant velocity. However, if the velocity of the object changes, then the accelerated motion is addressed by Newton's second law. The second law of motion describes how an object responds to an unbalanced force acting upon it. The law states that the acceleration of an object is directly proportional to the force exerted on it and inversely proportional to its mass. For example, when a person hits a ball, it moves with an acceleration directly proportional to the force applied to it.

The third law of motion, also known as the law of action and reaction, states that for every action, there is an equal and opposite reaction. For example, if a person stands on roller skates and throws a ball forward, then it is likely that the person will start moving backward at a given speed.

Newton's laws of motion have many applications in the real macroscopic world. For example, the laws can be used to design structures and machines that can withstand external forces. The trajectory of celestial objects or rockets can also be calculated using Newton's laws of motion.

In conclusion, Newton's laws of motion provide a foundation for understanding the relationship between forces and motion. These laws are fundamental to many fields of science and have practical applications that impact our daily lives. Whether we're watching a football game or launching a spacecraft, we rely on these laws to explain the motion of objects and the effects of forces on them.