100 Physics Ideas in 100 Words

g CONTENTS

Forces and Motion

Our lives are full of movement, from the natural world – people, birds, water, the wind – to human inventions such as cars and aircraft. Until the 16th century, the way things move was taken to be “natural” – a stone falls because its natural place is on the ground. Smoke rises because it has a natural property called “levity” that makes it move upwards. The Moon goes round the Earth because that’s what celestial bodies do.

However, this changed when scientists – particularly Italian astronomer Galileo Galilei and English physicist Isaac Newton – set about understanding what were the true “laws” that govern the motion of objects, both here on the surface of the Earth and beyond, in space. Although these laws ...