Define Motion and Laws of Motion

Motion

If an object changes its position with respect to its surroundings with time, then object is said to be in motion.

• The time rate of change of position of the object in any direction is called average speed.

• The shortest path between the final and the initial position of an object is called displacement.
• The rate of change of displacement of a body is called velocity.

• The rate of change of velocity of a body is called acceleration.

• If an object is travelling in a straight line at a constant speed, then it will not be accelerating.
• There are various type of motion like projectile motion, circular motion, rotational motion etc.
• Displacement, velocity and acceleration may be positive, negative or zero. But distance and speed are always positive.

Projectile Motion

• When an object is thrown obliquely near the Earth’s surface, its motion on a parabolic path, is known as projectile motion.
• To achieve maximum range, the body should be projected at an angle of 45°. Therefore, a long jumper takes jump at an angle of 45°.
• To achieve maximum height, the body should be projected at an angle of 90°.
• When a body is dropped freely from the top of the tower and another body is projected horizontally from the same point, both will reach ground at the same time.

Circular motion

When a body moves along a circular path, then its motion is called circular motion e.g. An artificial satellite orbiting the Earth at a constant speed, a fan’s blades rotating around a hub.

Rotational Motion

The motion of a rigid body which takes place such a way that all of its particles move in circles about an axis with common angular velocity, called rotational motion e.g. an oscillating table fan.

Newton’s Law of Motion

There are three laws of motion:-

1. First Law : “Every body retains its state of rest or state of motion until an external force is applied on it.” This law is also known as law of inertia or law of Galileo. Ex: A person standing in a bus falls backward and if bus is suddenly stops, then the person falls forward, due to inertia.
2. Second law: “It states that the rate of change of momentum of an object is proportional to the applied unbalanced force in the direction force. Ex. A cricket player moves his hand backwards on catching a fast cricket ball, to reduce the impact of catching the fast moving ball,
3. Third law:” For every action, there is an equal and opposite reaction and both act on two different bodies. Ex. It is difficult to fix a nail on a freely suspended wooden frame because the wooden block and nails both move forward on being hit.

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