Understanding Motion

Motion

• Everything around us is either in motion or at rest.
• Motion can be judged by comparing an object's position with respect to stationary landmarks.
• When an object's position relative to its surroundings does not change with time, it is at rest.
• When an object's position relative to its surroundings changes with time, it is in motion.

Motion is Relative

• All motion is relative.
• A boy sitting in a moving bus is at rest relative to the bus, but in motion relative to the road.

Types of Motion

• Random Motion: Motion without a pattern, e.g., a kite or a mosquito.
• Regular Motion: Motion that follows a pattern.
• Translatory Motion: Motion in a straight line, e.g., a bus or a ball thrown straight up or down.
• Rectilinear Motion: Motion along a straight line, e.g., vehicles on a straight road or athletes running on a track.
• Curvilinear Motion: Motion along a curved path, e.g., water from a garden hose.

Motion in Physics

Curvilinear Motion

• Motion of a body along a curved path, e.g., a vehicle turning from one road to another.

Rotatory Motion

• Motion of an object around an axis passing through itself, e.g., the rotation of the earth or an electrical fan.
• Examples: wheels of a car, food processors, and Ferris wheels.

Oscillatory Motion

• Motion of a pendulum, a swing, or a bell hanging by a cord.
• Not all swinging motions are oscillatory, e.g., swinging arms while walking.

Circular Motion

• Motion of a body around a fixed point, e.g., a string rotating around a hand.

Periodic Motion

• Any motion that repeats itself after a fixed interval, e.g., a clock's hands or the earth around the sun.
• Oscillatory motion is a type of periodic motion.

Simple Pendulum

• Consists of a small, heavy sphere (bob) suspended by a light string from a fixed support.
• Can oscillate freely when released from a small angle (< 4°) with the vertical.
• Mean Position: The position of the pendulum at rest, with the string vertical.
• Effective Length (l): The distance from the point of support to the centre of the bob.
• Amplitude: The angle of oscillation (< 4°) with the vertical.

Time Period

• The total time taken by one complete oscillation of a simple pendulum.
• Related to the length (l) and acceleration due to gravity (g) by the formula: T = 2π√(l/g)
• A pendulum with a time period of 2 seconds is called a seconds pendulum, used in clocks at one-second intervals.