In physics, a simple machine is any device that only requires the application of a single force to work. It is a tool used to make work easier. Machines use a force (push or pull) to move a load. Incline, Lever, Pulley, Wheel
The lever magnifies force or velocity. It is often used to move heavy loads with less effort. It is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object.
- Hammer and claw to remove nails.
The Wheel and Axle
The wheel and axle (axel) make it easier to move heavy loads along. A wheel is a disc- or torus-shaped object, the fundamental operation of which is to transfer linear motion (that is, going along) into rotary motion (that is, going around).
- Wagons and carts.
- Motorised vehicles (cars, trains, etc).
The pulley is one or more wheels on axles, with a rope going over each wheel. It makes it easier to lift heavy loads. It is a wheel with a groove along its edge, for holding a rope or cable. A first-class pulley has a fixed axle and is used to redirect the rope (called a belt when it goes in a full circle). A second-class pulley has a free axle, and is used to transform forces - when stationary the total force on the axle balances the total force provided by the tension in the rope (which is constant in magnitude in each segment).
- Flag hoist.
- Crane and jib.
- Engine block lifter in mechanics garage.
The Inclined Plane
The inclined plane makes it easier to raise heavy loads. It is a ramp that reduces the force necessary to overcome the force of gravity when changing the elevation of mass in a gravitational field.
- Wheelchair ramps.
- Loading ramps (e.g. into removals vans).
- The wedge and the screw use inclined planes to split objects or pull into objects.
All of these convert low forces into high forces or vice versa, and the ratio of the input force to the output force is the mechanical advantage. Mechanical advantage for a lever is equal to the ratio of the length of its two arms, for example, and the mechanical advantage for an inclined plane with the force acting parallel to the plane is the cosecant of the angle of inclination. The mechanical advantage of a simple machine is also affected by factors such as friction and elasticity, however, and so will usually differ somewhat from its theoretical value.
These simple machines fall into two general classes; those dependent on the vector resolution of forces (inclined plane, wedge, screw, toggle joint) and those in which there is an equilibrium of torques (lever, pulley, wheel). Simple machines are often used in combination as components of more complex machines; for example the Archimedes screw, which is a pump, is an example of a complex machine where the screw is a helical inclined plane.