A field is a quantity defined at every point in space. Gravity, electric force, magnetic force — all act through fields.
Quick check
What is a 'field' in physics?
Field lab — drag the source, follow the field
Field arrows point away from + and toward −; the dots are tiny positive test charges riding the field. Drag either charge.
Three fields you meet at school
- Gravitational — every mass makes one; always attractive; strength g = F/m.
- Electric — charges make one; can attract or repel; strength E = F/q.
- Magnetic — moving charges make one; acts on other moving charges; strength B in teslas.
Field lines are a drawing trick: closer lines mean a stronger field, and a small test object always feels a force *along* the line through its position.
Why bother with fields?
Newton disliked 'action at a distance' — how does the Sun pull the Earth across empty space? The field idea fixes it: the Sun fills space with a gravitational field, and the Earth responds to the field right where it sits. Electromagnetism and even gravity (general relativity) are field theories.