Minds On

How can we measure speed?

The following is an image of a tunnel and cars moving very quickly through this tunnel.

Cars moving quickly through a tunnel

How might we compare the speed of two objects, such as cars? Discuss with a partner, a small group, or brainstorm independently, how we measure speed.

Action

Rate

Speed is measured and defined as a fraction as DISTANCE OVER TIME.

The units of speed are expressed as fractions.

Next time you come across a speed limit sign, notice the units are often expressed as kilometres per hour (km/h). The kilometre (km) is a unit of distance, and the hour (h) is a unit of time.

A road sign that reads maximum 15 km slash h (kilometres per hour)

In proper standard fractional notation, we use a ― (line) with the numerator on top and the denominator on the bottom.

We come across the unit of speed kilometres per hour (km/h) as 1 kilometre IN ONE hour or 1 kilometre PER hour.

The speed limit sign 50 km/h (kilometres per hour) means that a vehicle cannot cover more than 50 kilometres IN ONE hour.

This means we multiply 50 times the unit speed of 1 kilometre IN ONE hour.

Practice

Write the following examples in the form of a fraction.

Compare the speeds in kilometres per hour (km/h) and order them from fastest to slowest.

A highway speed limit is 100 kilometres per hour (km/h).

A cheetah is the world’s fastest land mammal sprinting up to 113 kilometres per hour (km/h).

The sailfish is the world’s fastest fish moving at 109.4 kilometres per hour (km/h). Some scientists claim it moves at 113 kilometres per hour (km/h)!

The Peregrine falcon is the fastest winged animal moving at over 320 kilometres per hour (km/h) with the ability to plunge from great heights to do steep dives.

Consolidation

Speed check

A radar was recording speeds of drivers on a busy city road. The following are the most recent speeds of drivers on the road.

  • Car 1:  54 kilometres per hour
  • Car 2:  66 kilometres per hour
  • Car 3:  71 kilometres per hour
  • Car 4:  47 kilometres per hour
  • Car 5:  55 kilometres per hour
  • Car 6:  80 kilometres per hour
  • Car 7:  49 kilometres per hour
  • Car 8:  59 kilometres per hour
  • Car 9:  60 kilometres per hour
  • Car 10:  61 kilometres per hour

If the speed limit on this busy road is 60 kilometres per hour, which of the cars were speeding?

Write each speed as a fraction.

Order the cars from the fastest to the slowest.

Reflection

As you read through these descriptions, which sentence best describes how you are feeling about your understanding of this learning activity? Press the button that is beside this sentence.

I feel...

Now, record your ideas using a voice recorder, speech-to-text, or writing tool.

Press 'Discover More' to extend your skills.

Research the top 10 fastest land, water or winged animals in the world speeds in metric units. If there are decimal values, round to the nearest tens place value.

For each fastest land animal in the top 10, compare their speeds to determine which animals are the fastest to the slowest.