100 Physics Ideas in 100 Words

g CONTENTS

Force Fields

The idea of a field is very widespread in physics – we think of magnetic, electric and gravitational fields. A force field fills three-dimensional space and tells us about the force that will act on an object placed anywhere in the field.

If one magnet is brought close to another they may attract or repel one another, even though they are not touching. This “action at a distance” can seem surprising because we are used to objects exerting forces on each other when they are in contact. We explain it by saying that each magnet is surrounded by a magnetic field.

When astronomers first realised that an orbiting object such as the Moon required a force to hold it in its orbit – another example of action at a distance ...