Measuring speed accurately | Exit Quiz | Oak National Academy

Match the key words to the explanations.

• instantaneous speed

• overall distance travelled divided by overall time taken

• random error

• a difference in a measurement of time and the true time

• timing error

• unpredictable difference between measurement and true value

• average speed

• the speed at a particular moment

Answer explanation

Random errors are unpredictable and repeat readings can be used to reduce the effect. Timing measurements involve a reaction time between an event and stopping a clock. Instantaneous speed is at an instant and average speed is over a given time.

Tags

NGSS.MS-PS3-1

Select the reading that has a large timing error in this set of timing data.

• 4.25 s

• 4.15 s

• 3.25 s

• 4.20 s

• 4.20 s

Answer explanation

The reading 3.25 s is noticeably lower than all of the others, so it is likely to have a large timing error.

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.

• 2.5 s

• 1.6 s

• 2.1 s

• 2.9 s

• 2.2 s

Answer explanation

The speed is greatest for the shortest time and so the order is: 1.6 s then 2.1 s, 2.2 s, 2.5 s and finally 2.9 s.

Tags

NGSS.MS-PS3-1

Which of these will help to reduce timing errors in a trolley rolling experiment?

• Using a shorter track.

• Counting down before releasing the trolley and starting the watch together.

• Using a steeper track.

• Observing directly across the finish line.

• Using a stopwatch with a precision of 0.001 s.

Answer explanation

Counting down to release and observing along the finish line will reduce timing errors.

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.

• 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.

Answer explanation

As the time measured is too large and speed = distance ÷ time, the speed calculated will be too small.

Tags

NGSS.MS-PS3-1

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

• Making a video of the ball with a mobile phone

Answer explanation

Making a video of the event will mean you can pause it at the start and the end of the ball's journey and read off the time exactly.