Space and gravity, Year 8: more practice

Its lit half faces away from the Earth

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

The whyAt 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

HintThink about where the Moon is in its orbit.

The whyAt 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)

HintCount the cycle of phases on a calendar.

The whyThe cycle of phases takes about 29.5 days.

The Earth

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

The whyIn 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

HintOne measures kilograms.

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

The Moon's gravity is weaker

HintWeight depends on the pull of the body you stand on.

The whyThe 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

HintWhich way would an object fall?

The whyWeight is the pull of gravity, so it acts downwards towards the centre of the Earth.

80

HintW = m × g.

The why8 × 10 = 80 N.

80

HintW = m × g.

The why50 × 1.6 = 80 N. On Earth the same rock weighs about 500 N.

24

HintRearrange W = m × g.

The whym = W ÷ g = 240 ÷ 10 = 24 kg.