Typical speeds

1. Speed tells you how far an object travels in each second, and in physics it is measured in metres per second, $m/s$.
2. Most everyday speeds are not fixed, because they change with the person, the vehicle, the route and the conditions.
3. A typical speed is a sensible, rounded value that represents an activity, so it is an estimate rather than an exact measurement.
4. Knowing a small set of typical speeds lets you estimate times and distances for everyday journeys.
5. Typical speeds also let you check whether the answer to a calculation is realistic.
6. Typical speeds are usually given to one or two significant figures, because more figures would suggest a precision that the estimate does not have.

Walking, running and cycling

1. A person walking at a comfortable pace moves at about $1.5m/s$, which is roughly two steps every second.
2. A person running or jogging moves at about $3m/s$, so running is roughly twice as fast as walking.
3. A trained athlete sprinting can reach about $10m/s$, but only over a short distance.
4. A person cycling on a road moves at about $6m/s$, which is about four times walking speed.
5. These speeds depend on age, fitness, the slope of the ground, the surface and the distance to be covered, so a long uphill walk is slower than $1.5m/s$.

Road, rail and air transport

1. A car in a town or city usually travels at about $13m/s$, which is close to a $30$ mph speed limit.
2. A car on a motorway travels at about $30m/s$, which is close to the $70$ mph limit.
3. A bus in town moves at about $10m/s$ between stops, but its average speed over a whole journey is much lower because it stops often.
4. A fast train travels at about $50m/s$, and high-speed trains can travel faster than this.
5. A passenger ferry crossing the Channel travels at about $10m/s$.
6. A passenger aircraft cruising at height travels at about $250m/s$.
7. Comparing the values shows that a cruising aircraft is roughly $20$ times faster than a car in town and more than $150$ times faster than a person walking.

Wind and sound

1. Wind speed changes a great deal with the weather, so there is no single typical value.
2. A gentle breeze moves at about $3m/s$, a fresh wind at about $10m/s$ and a gale at about $20m/s$.
3. In a hurricane the wind speed is more than $30m/s$, which is faster than a car on a motorway.
4. Sound travels through air at about $330m/s$, which is much faster than any road vehicle.
5. The speed of sound in air changes a little with temperature, but $330m/s$ is the value to use in estimates.
6. Light travels about a million times faster than sound, so in a thunderstorm you see the lightning almost at once but hear the thunder later.
7. Each $3s$ between the flash and the thunder means the storm is about $1km$ away, because sound travels roughly $330\times 3\approx 1000m$ in that time.