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The Earth

Physics: Cambridge International GCSE Supplement, topic 6.1.1

The Earth

Basic facts

Basic facts

  • The Earth is a planet.
  • The Earth spins on its axis.
  • The axis is tilted.
  • The Earth makes one full spin in about 24 hours.
Apparent daily motion of the Sun

Apparent daily motion of the Sun

  • The spinning of the Earth around its axis causes the Sun to appear to move across the sky each day.
  • We call this the apparent daily motion of the Sun.
Day and night

Day and night

  • When our part of Earth faces the Sun, we see daylight.
  • When our part of Earth faces away from the Sun, we see night.
  • The tilt of the axis affects how long days and nights last in different seasons.
  • This cycle of day and night repeats every 24 hours.

The Earth's orbit around the Sun

The orbit

The orbit

  • The Earth moves around the Sun.
  • This movement is called an orbit.
  • The Earth takes about 365 days to complete one orbit.
Seasons

Seasons

  • The orbit of the Earth around the Sun causes the seasons to repeat every year.
  • The tilt of the Earth’s axis changes how sunlight falls on different parts of the Earth.
  • This is why we see summer, autumn, winter, and spring.
Orbital speed

Orbital speed

  • We can calculate the Earth’s average orbital speed.
  • The formula is v=2πrTv = \dfrac{2πr}{T}.
  • rr is the average radius of the orbit.
  • TT is the time the Earth takes for one orbit.

Test yourself on The Earth

  • What causes the apparent daily motion of the Sun across the sky?

  • What do we call the line that the Earth spins around?

  • How does the tilt of the Earth’s axis affect day and night?

  • What causes the repeating pattern of the seasons?

  • Why is Earth warmer in summer and colder in winter?

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