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.

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.

Try the lab to finish this lesson.