A light gate measures the time for a card of a fixed length to pass through it.
A radar gun measures changes in the frequency of reflected waves to measure speed.
A motion sensor can use reflected ultrasonic wave timings to measure changes in distance to determine speed.

Common misconception

Travelling at exceptionally high speed through a speed camera means that it will not be able to measure your speed accurately and so it will not trigger.

Tell pupils that speed cameras use radio waves which travel at 300 000 000 m/s. They can accurately measure the speed of objects travelling at thousands of metres per second.

Keywords

Speed camera - A speed camera is used to measure speed of vehicles on roads. It captures images of any vehicle exceeding the speed limit of the road.
Radar gun - A radar gun uses shifts in the frequency of reflected radio waves to measure the speed of objects.
Light gate - A light gate can be used to measure speed. It uses an infrared beam to turn a timer on and off as an object passes through.

Light gates allow for very accurate measurements of speed and vastly simplify measurements of acceleration in later lessons in the unit. If you have them, use them!

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).

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Starter quiz

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6 Questions

Q1.

Speed is a scalar quantity. Which of the following describes a scalar quantity?

It is a quantity that has magnitude (size) and direction.

Correct answer: It is a quantity that has only magnitude (size) and not direction.

It is a quantity that has only direction and not magnitude (size).

It is a quantity that has no direction and no magnitude (size).

Q2.

Match the the following objects with the example speeds.

Correct Answer:car on a motorway,70 mph

70 mph

Correct Answer:person walking,1.5 m/s

1.5 m/s

Correct Answer:snail moving across floor,10 cm/minute

10 cm/minute

Correct Answer:space station orbiting Earth,7.7 km/s

7.7 km/s

Correct Answer:sound wave in air,330 m/s

330 m/s

Q3.

A dog runs 80 m in 20 seconds. Which of the following calculations would give the speed of the dog?

speed = $$ 80 \text{ m} + 20 \text{ s}$$

speed = $$ 80 \text{ m} \times 20 \text{ s}$$

Correct answer: speed = $${ 80 \text{ m} \over 20 \text{ s}}$$

speed = $${ 20 \text{ s} \over 80 \text{ m}}$$

speed = $$ 80 \text{ m} - 20 \text{ s}$$

Q4.

A hot air balloon flies at a speed of 15 km/h for 5 hours. Which of the folloiwing is the distance it travels?

3 km

10 km

20 km

Correct answer: 75 km

150 km

Q5.

A sound waves takes 30 s to travel 45 000 m through water. Which of the following gives the speed of sound in water?

330 m/s

1350 m/s

Correct answer: 1500 m/s

15 000 m/s

1 350 000 m/s

Q6.

A dynamics trolley is rolled down a ramp reaching a speed of 2.4 m/s. Calculate the time it will take for the trolley to pass between a pair of markers which are 20 cm apart.

Correct Answer: 0.08 s, 0.08

Exit quiz

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6 Questions

Q1.

Match each of the following measuring devices to its description.

Correct Answer:light gate,sends signals to a timer when a passing object cuts its infrared beam

sends signals to a timer when a passing object cuts its infrared beam

Correct Answer:motion sensor,sends out sound pulses and the reflections from an object are detected

sends out sound pulses and the reflections from an object are detected

Correct Answer:radar gun,uses changes in frequency of reflected waves to measure speed

uses changes in frequency of reflected waves to measure speed

Correct Answer:speed camera,takes photos of road vehicles a short time apart

takes photos of road vehicles a short time apart

Q2.

A student measures the time taken for a trolley to travel down a ramp and get these measurements: 0.19 s, 0.18 s, 0.26 s, 0.17 s. Which of the following mean times should the student record?

Correct answer: 0.18 s

0.20 s

0.27 s

0.72 s

0.80 s

Q3.

A trolley with a card attached travels through a light gate, which measures the time for the card to pass through. Which of the following statements is correct if the trolley moves faster?

Correct answer: The measured time is shorter.

The measured time is longer.

The measured time is the same.

Q4.

A pair of speed cameras take photos of a car 0.50 s apart. The photos show that the car travelled 12 m during this time. The speed of the car is m/s.

Correct Answer: 24, 24m/s, 24 m/s

Q5.

A motion sensor sends out sound pulses. The pulses reflect off an object and return to the sensor after 0.0040 s. How far is the object from the sensor? The speed of sound in air is 330 m/s.

Correct answer: 66 cm

132 cm

165 cm

264 cm

Q6.

A trolley has a card of length 15 cm attached to it. The trolley passes through a light gate and the card cuts off the beam for 0.20 s. Which of the following is the speed of the trolley in cm/s?

0.75 cm/s

1.3 cm/s

3 cm/s

30 cm/s

Correct answer: 75 cm/s

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