номер 5, страница 75 - гдз по английскому языку 7 класс рабочая тетрадь Hardy-Gould, Mellersh

Gravity is the pulling force that holds us all down on the Earth's surface. The force of gravity gives us our weight: it makes us feel heavy.

Everything has a gravitational pull towards everything else; even two people attract each other. The bigger the object, the larger the pull, so the pull of the Earth is much more than the tiny pulls we have on each other. When we sit on a chair, gravity is pulling us down, but the chair is pushing up against us. Take the chair away and the pushing force disappears, and gravity pulls us onto the ground.

When there is no pushing force, gravity makes us fall freely. If we are in a lift and the cable breaks, the lift falls freely, and so do we. With nothing under us, we feel no weight. For a second, we feel weightless. When we are in orbit in space, we are falling towards the Earth but very slowly. We feel no support from our spacecraft because it is also falling towards the Earth. We feel weightless.

Weight = mass x gravity (w = mg). Mass is measured in kilograms (kg).

An elephant's mass (5,000 kg) never changes, but its weight can change because of gravity.

When gravity is weaker, objects are lighter. Weight is measured in Newtons (N).

On Earth 1 kg = 9.8 N.

So, the elephant weighs 5,000 kg x 9.8 N = 49,000 N.

On the Moon a kilo weighs 1.6 N. So, the elephant weighs 5,000 kg x 1.6 N = 8,000 N. The elephant is lighter on the Moon.