Measurement of
Time and Motion

We measure time using events that repeat in equal intervals — periodic events. The second is the standard unit: 60 s = 1 minute, 60 min = 1 hour.

• A simple pendulum (a bob on a thread) swings to and fro in equal times. One full to-and-fro swing is one oscillation; the time it takes is the time period.
• Because the time period stays steady, pendulums were used to run the first accurate clocks.

An object is in motion if its position changes with time; if it stays put, it is at rest. How quickly it moves is its speed:

speed = distance ÷ time

• Units: metre/second (m/s) or kilometre/hour (km/h).
• For the same distance, a faster object takes less time.
• To compare two speeds, always put them in the same units (1 m/s ≈ 3.6 km/h).

Once you can find speed, you can compare anything that moves. A walking person is about 1–2 m/s; a cyclist 5 m/s; a car on a highway 25 m/s (≈ 90 km/h); a cheetah, briefly, ~30 m/s.

To rank them fairly, work each one out as distance ÷ time and bring them to the same unit first — then the bigger number is simply faster.