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Year 8

Measuring speed accurately

I can clearly describe how to measure speed and explain how I can do this accurately.

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New
New
Year 8

Measuring speed accurately

I can clearly describe how to measure speed and explain how I can do this accurately.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. The instantaneous speed of an object is the speed at a particular moment in time.
  2. For an accurate measurement a person needs to be in line with the observation.
  3. Manual timing can lead to a range of timing errors.
  4. Repeat readings can reduce the effect of random errors.
  5. Some readings are anomalous and these should not be used in caluations of averages.

Common misconception

Students commonly confuse instantaneous and average speeds.

Be very careful when using the word speed, always use 'average' or 'instantaneous' explicitly, linking average speed to a time period.

Keywords

  • Average speed - The average speed of an object is the distance travelled divided by the time taken.

  • Instantaneous speed - The instantaneous speed of an object is its speed at a particular moment.

  • Timing error - Manual timings include some timing errors. These can be due to reaction times or observing from incorrect positions.

  • Random error - Random errors are errors that vary from test to test in an uncontrolled way.

Modelling movement with a motion sensor will really help show the difference between average and instantaneous speed. Move from one end of the room to the other while stating your instantaneous speed and then have students calculate average speed.
Teacher tip

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Video

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Starter quiz

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6 Questions

Q1.
Match the units to the quantities they are used to measure.
Correct Answer:metres (m),distance

distance

Correct Answer:seconds (s),time

time

Correct Answer:metres per second (m/s),speed

speed

Q2.
Which of these equations shows how distance travelled can be calculated from average speed and time?
distance travelled = speed - time
distance travelled = speed + time
distance travelled = speed ÷ time
Correct answer: distance travelled = speed × time
Q3.
Starting with the slowest, sort these objects in order of speed.
1 - snail: 1 mm/s
2 - spider: 10 cm/s
3 - cat: 1 m/s
4 - motorcycle: 10 m/s
5 - jet: 1 km/s
Q4.
A student measures how long a trolley takes to fall a distance of 1.5 m three separate times. Their readings are 2.5 s , 2.1 s, and 2.0 s. Calculate the average roll time.
2.0 s
Correct answer: 2.2 s
2.5 s
5.7 s
6.6 s
Q5.
A trolley was allowed to roll along a series of tracks of different steepness giving different average speeds. Starting with the slowest, sort the results in order of increasing average speed.
1 - ramp C: 2.4 s
2 - ramp B: 1.8 s
3 - ramp E: 1.7 s
4 - ramp A: 1.5 s
5 - ramp D: 0.9 s
Q6.
A toy car rolls through a distance of 3.2 m in a time of 1.6 s. Calculate the average speed of the trolley giving the correct unit.
Correct Answer: 2.0 m/s, 2 m/s, 2.0 metres per second, 2.0 mps, 2 mps

Exit quiz

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6 Questions

Q1.
Match the key words to the explanations.
Correct Answer:random error,unpredictable difference between measurement and true value

unpredictable difference between measurement and true value

Correct Answer:timing error,a difference in a measurement of time and the true time

a difference in a measurement of time and the true time

Correct Answer:instantaneous speed,the speed at a particular moment

the speed at a particular moment

Correct Answer:average speed,overall distance travelled divided by overall time taken

overall distance travelled divided by overall time taken

Q2.
Select the reading that has a large timing error in this set of timing data.
4.25 s
4.15 s
Correct answer: 3.25 s
4.20 s
4.20 s
Q3.
Five different trolleys are rolled along a 3.0 m track. Their times are shown. Starting with the fastest, put them into order of speed.
1 - 1.6 s
2 - 2.1 s
3 - 2.2 s
4 - 2.5 s
5 - 2.9 s
Q4.
Which of these will help to reduce timing errors in a trolley rolling experiment?
Using a shorter track.
Correct answer: Counting down before releasing the trolley and starting the watch together.
Using a steeper track.
Correct answer: Observing directly across the finish line.
Using a stopwatch with a precision of 0.001 s.
Q5.
Due to a timing error a student measures a time that is longer than the true time. How will this affect the speed they calculate for a rolling trolley?
There will be no effect.
The calculated speed will be faster than the true speed.
Correct answer: The calculated speed will be slower than the true speed.
The calculated speed will be random.
They will not be able to calculate a speed.
Q6.
Suggest which of the following items would be the most accurate way of measuring the time taken for a ball to be thrown across the lab?
using a timer on a mobile phone
reading the clock on the wall
using a school stopwatch
Correct answer: Making a video of the ball with a mobile phone