ch1

Got it! Here's the corrected and properly formatted version, keeping the content unchanged:

1.1 Speed

We can calculate the average speed of something moving if we know the distance it moves and the time it takes:

In symbols, this is written as:

v=dtv = \frac{d}{t}

where:

  • vv is the average speed

  • dd is the distance traveled

  • tt is the time taken

If an object is moving at a constant speed, this equation will give its speed during the time taken. If its speed is changing, then the equation gives us its average speed (calculated over a period of time).

  • Speedometer: If you look at the speedometer in a car, it doesn’t tell you the car’s average speed; rather, it shows the instantaneous speed (speed at a specific moment).

Key Equation

v=dtv = \frac{d}{t}

Units

In the Système Internationale d’Unités (SI):

  • Distance: Measured in metres (m)

  • Time: Measured in seconds (s)

  • Speed: Measured in metres per second (m s−1m \, s^{-1} or m/s)

Other units of speed may be used depending on the context:

Unit Description

m s−1m \, s^{-1}

Metres per second

cm s−1cm \, s^{-1}

Centimetres per second

km s−1km \, s^{-1}

Kilometres per second

km h−1km \, h^{-1}

Kilometres per hour

mph

Miles per hour

Note: Many calculations require speeds to be converted into SI units (m s−1m \, s^{-1}).

Example Question

Scenario:
Mo Farah has just run 10,000 m10,000 \, \text{m} in a time of 27 minutes 5.17 seconds27 \, \text{minutes} \, 5.17 \, \text{seconds}.

Task: Calculate his average speed during the race.

Table 1.1: Units of Speed

Unit Example Usage

m s−1m \, s^{-1}

Standard SI unit for speed

mm s−1mm \, s^{-1}

Small, precise measurements

km s−1km \, s^{-1}

Very high speeds (e.g., light)

km h−1km \, h^{-1}

Everyday speeds (e.g., cars)

Additional Questions

  1. Units of Speed:
    Choose appropriate units for the following scenarios:

    • A tortoise

    • A car on a long journey

    • Light

    • A sprinter

  2. Snail’s Speed:
    A snail crawls 12 cm12 \, \text{cm} in one minute. Calculate its average speed in mm s−1mm \, s^{-1}.