Fields in Physics
A field is the general idea of something having values through space (and time).
In physics it describes a force or influence that extends through space and time.
Objects with mass, like the Earth or an apple, are pulled towards each other over a distance.
You can jump really high but won't escape Earth's gravity field, you merely move within it and then get pulled back down.
Gravity changes through space: it gets weaker with distance.
Gravity changes over time: The Moon creates tides. The Sun, Planets, Moons, Comets, etc, are all in a gravitational dance.
Play with Gravity Freeplay to see the movements.
Types of Fields
The main types of field in physics are:
- You can move a paperclip without touching it! The region around the magnet exerts a force on the paperclip
- A compass needle shows the direction of the magnetic field
- You can feel the warmth from a fire without touching the flames
- your phone gets reception even though you are far from the nearest tower
Electric and Magnetic Fields
Here's how it works:
When an electric charge accelerates (not just moves at a constant speed, but changes its velocity) it produces electromagnetic waves.
These waves are ripples in the electromagnetic field that carry energy from one place to another, see Electromagnetic Spectrum to learn more.
Electromagnetism and Gravity are two of the four fundamental forces of nature.
Let's look at charged particles: we know there is an interaction between them: Opposites attract and like charges repel.
We can model that as a simple line between two charges.
But with many charges, all the interactions become hard to deal with:
But a model where each charge contributes to a field is easier to use, and gives a better feel for what is happening:
We can now imagine being anywhere in that field, with the lines pointing in the direction we feel force.
Play with Electric Field Animation.
- Gravity attracts masses together and creates a gravitational field
- Static electric charges create an electric field which can exert force on other charges.
- Moving electric charges (electric current) create a magnetic field which can influence magnets and other currents.
- Accelerating electric charges create waves in the electromagnetic field which carry energy of different frequencies from radio through light on to X-Rays and Gamma rays.