Clocks count repeats
Every clock needs something that repeats.
Old and new clocks
A wall clock, a wristwatch and a mobile phone all show the time. Inside, each one counts something.
What do all clocks count?
What this lesson covers
The idea
All clocks are based on some continuously repeating process that marks equal intervals of time; modern clocks use tiny, very rapid vibrations of a quartz crystal (quartz clocks) or of specific atoms (atomic clocks).
Old and new clocks
A wall clock, a wristwatch and a mobile phone all show the time. Inside, each one counts something.
What do all clocks count?
- Something that repeats again and again
- Something that moves only once
- Only the swings of a pendulum
What repeats inside?
Tap each clock to see what repeats inside it.
Equal intervals
The pendulum swings. The quartz crystal vibrates very fast. Atoms vibrate. Each repeats continuously and marks equal intervals of time.
All clocks are based on some continuously repeating process that marks equal intervals of time. Modern clocks use tiny, very rapid vibrations of a quartz crystal (quartz clocks) or of specific atoms (atomic clocks).
Notes
All clocks are based on some continuously repeating process that marks equal intervals of time. Modern clocks use tiny, very rapid vibrations of a quartz crystal (quartz clocks) or of specific atoms (atomic clocks).
Check yourself
All clocks are based on a process that …
A quartz clock uses the vibrations of …
An atomic clock uses the vibrations of …
Which clock is the most precise?
- happens only once. A clock needs a process that repeats, to mark equal intervals of time.
- is different every time. Equal intervals need a process that repeats in the same way.
- repeats continuously and marks equal intervals of time — correct. Yes!
- a quartz crystal — correct. Yes!
- an atom. Atomic clocks use the vibrations of specific atoms.
- a pendulum. Pendulum clocks use a pendulum.
- a quartz crystal. Quartz clocks use a quartz crystal.
- specific atoms — correct. Yes!
- a candle flame. A candle clock burns a candle. An atomic clock uses atoms.
- A candle clock. A candle clock is only a rough way to measure time.
- An early pendulum clock. Early pendulum clocks could gain or lose 10 seconds each day. Atomic clocks lose only one second in millions of years.
- An atomic clock — correct. Yes!