Simple Machines: A Comprehensive Guide to Mechanical Advantage

Simple Machines and Mechanical Advantage

Simple machines are devices that make work easier. They do this by changing the magnitude or direction of a force. Many simple machines are combined to create complex machines.

Wheel and Axle

A wheel is attached to a central axle so that when one turns, the other must turn. A longer motion at the wheel's edge is converted to a shorter, more powerful motion at the axle. Conversely, a short, powerful force at the axle moves the wheel's edge a greater distance.

Pulley System

A single pulley simply reverses the direction of a force. When two or more pulleys are connected together, they permit a heavy load to be lifted with less force. The trade-off is that the rope's end must move a greater distance than the load.

Wedge

A wedge converts motion in one direction into a splitting motion at right angles to the blade. Nearly all cutting machines use the wedge. A lifting machine may use a wedge to get under a load.

Screw

A screw is a central rod with a thread or groove wrapped around it to form a helix. While turning, a screw converts rotary motion into a forward or backward motion.

Lever

A lever is a stiff rod that rotates around a pivot point. Downward motion at one end results in upward motion at the other. Depending on the pivot point's location, a lever can multiply either the applied force or the distance over which the force is applied.

Gears

Gears are toothed wheels meshed together to transmit motion and force. In any pair of gears, the larger one rotates more slowly than the smaller one but with greater force. Each gear in a series reverses the direction of rotation of the previous gear.

Bevel Gears

Bevel gears, which mesh at an angle, change the direction of rotation.

Worm Gear

A worm gear combines a gear meshed with a screw's threads. This combination changes the direction of turning motion by ninety degrees. Worm gears also decrease the speed of turning from screw to gear and increase its force.

Rack and Pinion

A pinion (single gear) meshes with a sliding toothed rack. This combination converts rotary motion to back-and-forth motion. Car windshield wipers are powered by a rack and pinion mechanism; a small pinion at the wiper's base meshes with a sliding rack below.

Cam

A cam is a wheel with shaped bumps. Cams are often connected to rods, levers, or springs. In a gravity trip hammer, the bumps on the turning cam push down on the lever's end, raising the hammer repeatedly.

Crank and Rod

A crank is a wheel with a pivoting arm attached near its edge. The arm is hinged to a rod. When the crank turns, the rod is pushed back and forth. Alternatively, if the rod is pushed back and forth at the right speed, the crank will turn. The crank and rod shown here are part of a giant steam engine.

Chains and Belts

A chain or belt connects two separated wheels so that when one turns, the other turns in the same direction.

Ratchet

A ratchet allows a wheel to turn in only one direction. The ratchet wheel has specially shaped teeth. A pivoted bar, called the pawl, is fixed above the ratchet wheel. The pawl slides over the teeth in one direction but blocks motion if the wheel turns the other way.