By accelerating particles to very high energies and smashing them into targets, or into each other physicists can unravel the forces acting between them.

Accelerators come in two types, linear (see the LINAC) and circular. Accelerators use powerful electric fields to push energy into a beam of particles - causing an increase in velocity and kinetic energy. Magnetic fields are used to keep the beam tightly focused, and in circular machines to steer the particles around the ring. See the cyclotron and the synchrotron.

Linear machines push energy into the beam all along the accelerator's length. The longer the machine, the higher the final energy, but this has practical implications!

In circular machines the particles go round and round again, collecting energy with each lap. But the faster the particles are going, the more they try to 'skid' off the ring, just like cars going round a tight curve in the road. CERN's biggest accelerator, the Large Electron Positron collider LEP, is 27 kilometres round, keeping the curves as gentle as possible.