Space and gravity, Year 8: more practice

Its lit half faces away from the Earth

提示The Moon is still there; think about which side the Sun lights.

为什么At new Moon, the Moon is between the Earth and the Sun, so the sunlit half faces away from us.

The whole of its lit half faces the Earth

提示Think about where the Moon is in its orbit.

为什么At full Moon, the Moon is on the far side of the Earth from the Sun, so we look at the whole sunlit half.

About a month (29.5 days)

提示Count the cycle of phases on a calendar.

为什么The cycle of phases takes about 29.5 days.

The Earth

提示The body we live on blocks the Sun's light from reaching the Moon.

为什么In a lunar eclipse the Sun, Earth and Moon are in a line with the Earth in the middle. The Moon is in the Earth's shadow.

A balance

提示One measures kilograms.

为什么A balance compares masses and gives kg. A newtonmeter measures a force, weight, in newtons.

The Moon's gravity is weaker

提示Weight depends on the pull of the body you stand on.

为什么The Moon is smaller than the Earth, so its gravitational field strength is lower, so the same mass is pulled less. Mass is unchanged.

Towards the centre of the Earth

提示Which way would an object fall?

为什么Weight is the pull of gravity, so it acts downwards towards the centre of the Earth.

80

提示W = m × g.

为什么8 × 10 = 80 N.

80

提示W = m × g.

为什么50 × 1.6 = 80 N. On Earth the same rock weighs about 500 N.

24

提示Rearrange W = m × g.

为什么m = W ÷ g = 240 ÷ 10 = 24 kg.