How exact is a clock?
Two clocks start together. After a month, an early pendulum clock could be 5 minutes wrong. A quartz watch is a common battery watch. After a month, it could be 15 seconds wrong.
Step 1 of 3
- An early pendulum clock: could be 5 min off after 30 days.
- A quartz watch: up to about 15 s off in a month.
- An atomic clock: almost no error.
The new words
A vibration is a quick back-and-forth shake. Atoms are the tiny particles that make up matter.
- Quartz clock — counts the tiny vibrations of a quartz crystal.
- Atomic clock — counts the vibrations of atoms.
- Drift — how far a clock gets wrong as time passes.
The rule
A clock gains time if it runs fast. It loses time if it runs slow.
A good clock gains or loses very little time. A quartz clock counts the vibrations of a crystal. An atomic clock drifts by about one second in millions of years.
Early pendulum clocks could drift 10 s or more a day. Take 10 s a day. In 30 days, 10 × 30 = 300 s. Then 300 ÷ 60 = 5 min.
Now try it. Pick a clock. Pick how long it runs.
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