Motion and Time

We say something is fast or slow by comparing how much distance it covers in a given time. A cheetah covers 120m in 1 second; a tortoise covers 0.003m in 1 second. Speed helps us compare motions objectively without saying just "fast" or "slow".

Speed = Distance / Time. SI unit: m/s (metres per second). Also used: km/h, cm/s. Uniform speed: same speed throughout (car on straight highway). Non-uniform speed: speed changes (car in city traffic). Speedometer in car measures instantaneous speed.

Plotting distance (y-axis) vs time (x-axis). Straight line through origin = uniform speed (slope = speed). Flat horizontal line = object at rest. Steeper slope = faster speed. Curved line = non-uniform speed (changing speed).

Ancient methods: sundial (shadow), water clock, hourglass. Modern: quartz clock (vibration of quartz crystal at 32,768 Hz), atomic clock (vibration of cesium-133 atom). Simple pendulum: T = 2π√(L/g). Time period depends only on length, not mass or amplitude (for small oscillations).