# Measuring time intervals

##### Class practical

Practice in estimating time and measuring time.

#### Apparatus and materials

As many different time measuring devices as possible, including

Wall clock

Wrist watch (to allow the use of the human pulse as a timer)

Laboratory timers, electronic (ideally ones with different scale intervals, e.g. 0.1 s, and 0.01 s)

Sand hourglass / egg timer

Kitchen timer (either wind-up or digital)

Electronic timers or datalogging package, OPTIONAL

#### Health & Safety and Technical notes

Some mobile phones also have in-built timers which can be used.

#### Procedure

a Ask students to make some rough measurements of time, to gain familiarity both with time intervals, e.g. of the time between hand claps, the time for a book to drop, the time to walk or run a given distance and stopwatches and other measuring devices.

b Have them measure (or attempt to measure) the same time interval with a variety of devices.

#### Teaching notes

1 This activity can begin with students estimating time intervals between various activities and then by measuring time intervals to check how good their estimates are. Young students will find five minutes of silence to be a life sentence!

Some real tasks will improve motivation, e.g. measuring the time to run a 100 m race. Average speed measurements might also be included, e.g. the time taken for a ball to fall from a high window.

2 Discuss the difference between timing an unexpected time period (e.g. between hand claps hidden under a desk) compared to something that they can predict (e.g. a falling object).

3 There are many electronic timers and datalogging packages available for measuring time, which will make a change from stopwatches and provide an introduction to electronic time measurement.

4 How Science Works extension: The selection of appropriate equipment to carry out a particular measurement is an important skill that is often overlooked, particularly if the ‘correct’ equipment for any experiment is generally made available for students. Students need practice choosing equipment and justifying their choice if they are to become confident experimenters.

This activity allows students to look at different ways of measuring time and to compare uncertainties in measurements. They could also discuss measurement errors. Point out that no single timing device will suit all situations.

This experiment was safety-checked in July 2007