Using the ticker-timer to measure time

Class practical

This is a useful introduction to the use of ticker-timers.

Apparatus and materials

For each student or student group

Ticker-timer

Ticker-tape

Stopwatch or stopclock

Mechanics trolley or wind-up/pull-back toy car OPTIONAL

Health & Safety and Technical notes

In crowded laboratories, estimate the space needed by the tape puller and arrange the groups to avoid collisions.

The ticker-timer should come with a recommended power supply unit (low voltage AC as specified, with on/off switch).

Some ticker-timers use light-developed tape rather than carbon discs. After the tape has been struck with the vibrating arm, it takes a few minutes for the dots to become visible.

Procedure

a Thread a short length of ticker-tape through the ticker-timer. If there is a carbon paper disc, make sure the tape goes underneath the disc.

b Turn the ticker-timer on for a few seconds. It vibrates rapidly and hits the top of the carbon paper. It makes a lot of dots on the tape, at regular intervals.

c Remove the tape from the ticker-timer. If the tape didn't move when the ticker-timer was switched on, then all the dots will be in the same place.

d Thread a longer piece of ticker-tape, about 1 metre long, through the ticker-timer. Switch the ticker-timer on. Pull the tape slowly through the ticker-timer.

e Check the tape to see if you can see each individual dot, with a space between. We can say that each dot-to-dot space stands for a 'tick' of time.

f Thread another 1 metre piece of tape through the ticker-timer.

g You need a 'start' signal and a 'stop' signal. These could be handclaps by one of your group or by your teacher. They should be just a few seconds apart. Pull the tape slowly and switch the ticker-timer on at the start signal. Switch it off at the stop signal.

h Count the number of dot-to-dot spaces between the start and the stop. That is the time between the signals, measured in 'ticks'.

i Use a fresh piece of tape, and a stopwatch or stopclock. Pull the tape through the ticker-timer for 3 seconds. Find out how many 'ticks' there are in 3 seconds. Find out how many there are in 1 second. Work out the time in seconds that is the same as 1 tick.

Teaching notes

1 All students could use the same start and stop signals, such as two handclaps by the teacher. This provides the opportunity for comparison of the times obtained by different students. Times can be tabulated, and used for discussion of range, mean and estimated error.

2 You could make a bar chart of students' answers for the time, in seconds, that is equivalent to one tick. Most ticker-timers vibrate at 50 Hz, and thus make 50 dots per second. For these, the expected mean value of one tick is 1/50 second, or 0.02 s. (Some ticker-timers will give dot-making frequency of 100 Hz, and for these the value of one tick is equivalent to 1/100 seconds or 0.01 s.)

3 You can make a model of the action of the ticker-timer and the ticker-tape. Move a roll of wallpaper along the bench or floor and ask a student to put blobs of paint or ink onto the wallpaper at regular times. These could be indicated by a steady handclap or a metronome. Fast and slow motion by the 'wallpaper puller' will produce blobs at different separations for equal time intervals. Each blob-to-blob space represents a 'tick' of time.

4 How Science Works extension: This activity can be used as a prompt to discuss the relative merits of the ticker-timer as a timing device compared to a stopwatch. Make a simple speed measurement for a moving object such as a mechanics trolley or a pull-back car using the ticker-timer and conventional stopwatch. Encourage students to discuss or write about the strengths and weaknesses of each method. The key teaching point is how to select appropriate equipment, by using the concepts of accuracy and uncertainty in measurements.

Many students find the ticker-timer an awkward piece of equipment. Some struggle to get a time reading from the paper tape and get confused about what the dot spacings represent. If you plan to use ticker-timers regularly in motion experiments, give students extra time with early investigations so they become familiar and confident with the equipment.

This experiment was safety-checked in January 2007