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Class 7 Science — Measuring time

Say how old clocks kept time, find a pendulum's time period from a count of oscillations, and convert between the second, the minute and the hour.

Name: ________________________

Before you start

The parts of a simple pendulum, and where the bob reaches at one extreme.

1234
  1. 1. The support
  2. 2. The thread
  3. 3. The bob
  4. 4. One extreme

The dark bob hangs at the mean position, straight below the support. The pale one shows where it reaches at one extreme; there is a matching extreme on the other side. One oscillation is mean, extreme, across to the other extreme, back to mean.

  1. 1.What does a quartz clock count to keep time?

    • a) The swings of a very short pendulum
    • b) Drops of water falling through a fine hole
    • c) The turning of gears driven by a hanging weight
    • d) Very rapid vibrations of a quartz crystal

  2. 2.A sundial, an hourglass and an atomic clock look nothing alike. What do they have in common?

    • a) Each of them can measure a thousandth of a second
    • b) Each of them counts a process that repeats at a steady rate
    • c) Each of them was invented in the same century
    • d) Each of them needs sunlight to work

  3. 3.Two pendulums hang side by side. They are the same length, but one has a much heavier bob. What can you say about their time periods?

    • a) They are the same, because the time period depends on length rather than on the mass of the bob
    • b) There is no way to say without timing them
    • c) The heavier bob gives the shorter time period, because it swings with more force
    • d) The heavier bob gives the longer time period, because it is harder to move

  4. 4.A journey takes 6 hours. How many minutes is that? Answer with a number.

  5. 5.Match each old timekeeping device to the steadily repeating thing it counted.

    • Sundial
    • Water clock
    • Hourglass
    • Candle clock
    • water flowing out of, or into, a vessel
    • a marked candle burning down
    • sand running from one bulb to the other
    • the moving shadow an object casts in sunlight

  6. 6.Put the stages of one oscillation of a pendulum in order, starting from the moment the bob leaves the mean position.

    • It swings across to the other extreme position and turns
    • It reaches one extreme position and turns
    • The bob leaves the mean position
    • It arrives back at the mean position

  7. 7.The time a pendulum takes to complete one oscillation has a two-word name. What is it?

  8. 8.What is the SI unit of time? Give the word, not the symbol.

Answer key — Class 7 Science — Measuring time

  1. 1. d) Very rapid vibrations of a quartz crystal
  2. 2. b) Each of them counts a process that repeats at a steady rate
  3. 3. a) They are the same, because the time period depends on length rather than on the mass of the bob
  4. 4. 360
  5. 5. Sundial → the moving shadow an object casts in sunlight; Water clock → water flowing out of, or into, a vessel; Hourglass → sand running from one bulb to the other; Candle clock → a marked candle burning down
  6. 6. 1. The bob leaves the mean position 2. It reaches one extreme position and turns 3. It swings across to the other extreme position and turns 4. It arrives back at the mean position
  7. 7.
    • time period
    • the time period
  8. 8. second