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Year 9

Speed of sound

I can measure the speed of sound waves in air using an echo method.

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New
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Year 9

Speed of sound

I can measure the speed of sound waves in air using an echo method.

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Lesson details

Key learning points

  1. The ‘speed of sound’ is the distance travelled by a sound wave pulse every second, measured in m/s.
  2. Sound wave speed depends on the medium: it is about 340 m/s in air, faster in liquids and faster still in solids.
  3. Sound waves can reflect from hard surfaces, travel back and be heard again (an echo).
  4. The speed of sound waves (or the distance they travel) can be calculated using the equation: speed = distance ÷ time.
  5. In an experiment, measuring longer distances and times means any errors are a smaller proportion of the measurements.

Keywords

  • Speed - how fast something is moving, often measured in metres per second

  • Sound wave - a ‘pulse’ that travels through a material caused by forward and backward vibrations of particles

  • Medium - the material through which a wave travels

  • Frequency - the number of vibrations each second

  • Echolocation - a method of detecting distances to objects by making a sound and waiting for an echo to return

Common misconception

High pitched sounds (higher frequency sound waves) travel faster than low pitched sounds (lower frequency sound waves).

Take measurements for the speed of sound using a high-pitched blast of a whistle as well as the lower pitched sound of hitting pieces of wood together to show they are the same (within error).

It is advisable to trial the experiment at your chosen location (with low and high pitched sounds) before doing with a class. Consider if this can be filmed to show in class in case of bad weather. Teachers could also consider whether the experiment will work best as a demo. or a class practical.
Teacher tip

Equipment

a long tape measure or trundle wheel, timer, blocks of wood, whistle, a suitable outdoor space with a large distance (over 80 m) and a large, hard vertical wall

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).

Lesson video

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Starter quiz

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6 Questions

Q1.
A car’s speedometer shows a speed of 20 miles per hour. What does this mean?
The car has travelled for an hour and covered a distance of 20 miles.
Correct answer: If the car continued for an hour at this speed, it would travel 20 miles.
If the car continued for 20 hours at this speed, it would travel 20 miles.
The car has travelled for 20 hours and covered a distance of a mile.
Q2.
Which of the following describes the medium of a wave?
It is another word for the amplitude.
Correct answer: It is the material the wave travels through.
It is half-way between a peak and a trough.
It is the distance between one peak and the next.
Q3.
Which of the following can describe the motion of particles in sound waves?
Correct answer: back and forth
forwards
Correct answer: left and right
to the right
Correct answer: up and down
Q4.
Which of the following can sound travel through?
a vacuum
Correct answer: solids
Correct answer: liquids
Correct answer: gases
Q5.
Which of the following statements about the speed of sound waves in solids, liquids and gases are correct?
It is higher in liquids than solids, as particles in liquids move faster.
Correct answer: It is higher in liquids than gases, as particles in liquids are closer together.
Correct answer: It is higher in solids than liquids, as attractions are stronger in solids.
It is higher in gases than liquids, as particles in gases are more free to move.
Q6.
Which of the following is the best definition of experimental errors?
writing down measurements incorrectly
Correct answer: differences between measured values and the true values
ways in which the method of an experiment could be improved
mistakes made by the experimenter when carrying out the experiment

Exit quiz

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6 Questions

Q1.
Which of the following statements are correct?
All sound waves travel at the same speed.
All sound waves have the same frequency.
Correct answer: The frequency of a sound wave affects the pitch of the sound heard.
The frequency of a sound wave affects its speed in a particular medium.
Q2.
A bird is flying at a constant speed. In 3.5 s, it travels 42 m. The speed of the bird is m/s.
Correct Answer: 12, 12.0, 12m/s
Q3.
Two pupils use an echo method to measure the speed of sound in air. The diagram shows the arrangement. When should the pupil start and stop the timer?
An image in a quiz
Start when the blocks hit; stop when the sound hits the wall.
Correct answer: Start when the blocks hit; stop when they hear the sound a second time.
Start when the sound hits the wall; stop when they hear the sound a second time.
Q4.
Two pupils measure the speed of sound. The time between making a sound and hearing its echo from a wall 150 m away is 0.94 s. The sound speed they calculate, written to 2 s.f., is m/s.
Correct Answer: 320
Q5.
A ship uses sonar to find the distance to an underwater object, by measuring the time taken for sound to return after reflecting from the object. This technique, also used by dolphins, is called .
Correct Answer: echolocation, echo location, echolocating, echo locating
Q6.
A sonar system on a ship sends out a sound wave and receives an echo 1.20 s later. How far away is the object, if the speed of sound in water is 1500 m/s?
625 m
Correct answer: 900 m
1250 m
1800 m

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