Speed
Speed is the rate at which an object covers distance, defined as the total distance travelled divided by the time taken. It is a scalar quantity, possessing magnitude but no direction, and is always non-negative. Average speed is useful for describing overall motion, while instantaneous speed gives the speed at any particular moment.
Key Formula
v_avg = d / t
LaTeX: v_{avg} = \frac{d}{t}
| Symbol | Meaning | Unit |
|---|---|---|
| v_avg | Average speed | m/s |
| d | Total distance travelled | m |
| t | Time taken | s |
Worked Example
Problem
A cyclist completes a 60 km route in 2.5 hours. What is the cyclist's average speed in km/h and m/s?
Solution
Step 1: Average speed = distance / time = 60 km / 2.5 h = 24 km/h. Step 2: Convert to m/s: 24 km/h × (1000 m / 1 km) × (1 h / 3600 s) = 24000 / 3600 ≈ 6.67 m/s.
Answer
Average speed = 24 km/h ≈ 6.67 m/s.
Typical speeds of common objects
| Object | Speed (m/s) | Speed (km/h) | Notes |
|---|---|---|---|
| Tortoise | 0.07 | 0.27 | Approximate walking speed |
| Human walking | 1.4 | 5 | Comfortable pace |
| Bicycle | 5–10 | 18–36 | Leisure to moderate cycling |
| Car (highway) | 28 | 100 | Indian highway speed limit |
| Sound in air | 343 | 1235 | At 20°C at sea level |
| Light in vacuum | 3 × 10⁸ | 1.08 × 10⁹ | Universal maximum |
Interactive Tools
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Related Terms
Velocity
Velocity is the rate of change of displacement with respect to time, making it a vector quantity with both magnitude (speed) and direction. Average velocity equals total displacement divided by total time, while instantaneous velocity is the derivative of position with respect to time. Velocity is central to Newton's laws and is measured in metres per second (m/s).
Distance
Distance is the total length of the path travelled by an object, regardless of direction. It is a scalar quantity, meaning it has magnitude only and is always non-negative. Distance differs from displacement because it tracks the entire route rather than the straight-line separation between start and finish.
Acceleration
Acceleration is the rate of change of velocity with respect to time, and is a vector quantity. An object accelerates whenever its speed changes, its direction changes, or both simultaneously. Acceleration is caused by a net force (Newton's second law) and is measured in metres per second squared (m/s²).
From Old English "sped" (success, quickness), related to Old High German "spuot". In physics, the modern scalar meaning was formalised in the 17th–18th centuries to distinguish rate-of-distance from directional velocity.