Speed and velocity describe how fast motion occurs. We cover definitions, units, types, conversion, measurement, and applications.
What are Speed and Velocity?
Speed is scalar: distance/time. Velocity is vector: speed with direction.
Key Concept:
Constant speed on a circle still means changing velocity because direction changes.
Units of Speed and Velocity
Metric System
- m/s (SI)
- km/h (vehicles)
- cm/s (slow)
Imperial/US
- mph
- ft/s
- knots (nautical)
Types of Speed and Velocity
Instantaneous
At a specific moment (speedometer).
Average
Total displacement / total time.
Relative velocity
Observed from a moving frame.
Terminal velocity
Drag balances weight in freefall.
Speed and Velocity Conversion Table
| Unit | m/s | km/h | mph | knots |
|---|---|---|---|---|
| 1 m/s | 1 | 3.6 | 2.237 | 1.944 |
| 1 km/h | 0.2778 | 1 | 0.6214 | 0.54 |
| 1 mph | 0.447 | 1.609 | 1 | 0.869 |
| 1 knot | 0.514 | 1.852 | 1.151 | 1 |
Measuring Speed and Velocity
Radar gun
Doppler effect for moving objects.
Pitot tube
Static vs dynamic pressure in fluids/aircraft.
LDV
Laser Doppler velocimetry for particles/flows.
Applications of Speed and Velocity
Transportation
- Speed limits
- Vehicle testing
- ATC
- Navigation
Sports
- Pitch speed
- Serve velocity
- Swing speed
- Performance analysis
Meteorology
- Wind speed
- Storms
- Forecasting
- Climate models
Industrial
- Conveyors
- Pipe flows
- Manufacturing
- Robotics
Did You Know?
Parker Solar Probe exceeds 700,000 km/h; hypersonic aircraft like X‑43A reached Mach 6.
Speed and Velocity in Everyday Life
Common speeds
- Walk ~1.4 m/s
- Sprint ~10 m/s
- Cycle ~6 m/s
- Highway ~30 m/s
- Airliner ~250 m/s
Nature
- Sound ~343 m/s
- Light 3×10^8 m/s
- Earth rotation ~460 m/s
- Earth orbit ~29,800 m/s
Practical Tip:
Mind units: 1 m/s = 3.6 km/h; 1 mph ≈ 1.61 km/h. Velocity needs direction; draw vectors.