Coral wants her bike wheel's period. She spins the wheel and times one revolution with a stopwatch. Her thumb is late at the start and early at the stop.
One revolution is over too fast to time well. How does she get an accurate period?
Time many revolutions instead of one.
Coral counts 30 complete revolutions while her stopwatch runs: the total time is 45 s.
Each revolution took an equal share of that total.
A thumb slip of 0.2 s now spreads across all 30 revolutions, so each revolution's share of the slip is less than 0.01 s.
Count complete revolutions only: a revolution still in progress when the stopwatch stops is not counted.
Coral counts 30 complete revolutions of her bike wheel in 45 s. Calculate the period.
Write down the values:
total time = 45 s, revolutions = 30, T = ?
Write down the equation:
period = total time ÷ number of revolutions
Substitute in the values, and calculate:
T = 45 / 30 = 1.5
The wheel's period is 1.5 s.
Coral oils the bearings and spins the same wheel again: 30 complete revolutions in 36 s. Calculate the period now.
Write down the values:
total time = 36 s, revolutions = 30, T = ?
Write down the equation:
period = total time ÷ number of revolutions
Substitute in the values, and calculate:
T = 36 / 30 = 1.2
The wheel's period is now 1.2 s.
A box fan's blade completes 50 revolutions while Dagny times 20 s. Which division gives the period?
The same box fan: 50 complete revolutions in 20 s. Enter the period in s.
A wind turbine blade completes 12 revolutions in 90 s. Enter its period in s.
A record turntable completes 25 revolutions in 54 s. Enter its period in s.
Astrid times 40 revolutions of a wheel instead of one. Why does timing many revolutions give a more accurate period?
Bruno watches an old mill's water wheel for 140 s and counts 20 complete turns in that time. Enter the period in s.