An exercise machine is any machine used for physical exercise. These range from simple spring-like devices to computerized electromechanical rides to recirculating-stream swimming pools. Most exercise machines incorporate an ergometer. An ergometer is an apparatus for measuring the work a person exerts while exercising as used in training or cardiac stress tests or other medical tests.
Weight machines use gravity as the primary source of resistance, and a combination of simple machines to convey that resistance, to the person using the machine. Each of the simple machines (pulley, lever, wheel, incline) changes the mechanical advantage of the overall machine relative to the weight.
Ellipticals (elliptical machines) are a combination of stair-climbing and a treadmill. Generally it contains two tracks upon which the user stands; when he or she moves his or her legs, they describe an elliptical motion (hence the machine name). Some ellipticals have magnetic resistance controls that add difficulty to doing the motion.
This machine allows the user to stand on two separate foot pedals and use their own muscles to create the movement. The stabilized movement can be likened to that of a "swing set" for each leg.
Also named stair-climbing machines, they work the user's legs as he/she pumps pedals up and down, much like climbing stairs. Some climbing machines have handles to push and pull to exercise the whole body.
Rowing machines, also named rowers, simulate the body movements of using a rowing boat.