Five (or six) Simple Machines

1  Lever (s)

1.1  A lever is a stiff rod (lever) that rotates around a pivot point (fulcrum). Downward motion at one end results in upward motion at the other end. Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the force is applied. There are three types of levers:

2  Wheel and Axle

2.1  A continuous second class lever.  In this machine a wheel or spoke is locked to a central axle so that when one is turned the other must turn. A longer motion at the edge of the wheel is converted to a shorter more powerful motion at the axle. In reverse, a short powerful force at the axle will move the wheel's edge a greater distance.

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

2.1.1.1  Bevel Gears Gears that mesh at an angle change the direction of rotation.

2.1.1.2  The Worm Gear A worm gear is a combination of a gear meshed with the threads of a screw. 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.

2.1.1.3  The Rack and Pinion A single gear, the pinion, meshes with a sliding toothed rack. This combination converts rotary motion to back and forth motion. Windshield wipers in cars are powered by a rack and pinion mechanism. A small pinion at the base of the wiper meshes with a sliding rack below.

2.1.1.4  Cam A cam is a wheel with shaped bumps on it. Cams are often connected to rods, levers, or springs. In the gravity trip hammer shown here, the bumps on the turning cam push down on the end of the lever making it raise the hammer again and again.

2.1.1.5  The Crank and Rod The crank is a wheel with a pivoting arm attached near its edge. The arm is attached by a hinge 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 giant steam engine.

2.1.5  Chains and Belts A chain or belt connects two separated wheels so that one turns, the other will turn in the same direction.

2.1.1.6  The Ratchet A ratchet is a device that allows a wheel to turn in only one direction. The ratchet wheel has specially shaped teeth. A bar on a pivot called the "pawl" is fixed above the ratchet wheel. The pawl slides over the teeth of the ratchet in one direction, but blocks the motion of the teeth if the wheel turns in the other direction.

3  Sheave & Line System (pulley)

3.1  A sheave and line are a continuous first class lever. A single sheave simply reverses the direction of a force. When two or more sheaves are connected together, they permit a heavy load to be lifted with less force. The trade-off is that the end of the line must move a greater distance than the load. There are three basic types of sheaves:

3.2  Fixed Sheaves: A sheave in which the wheel does not move. Fixed sheaves change the direction of the effort force. It does not increase the size of the effort force. The effort force is equal to the resistance force in a fixed pulley; therefore, the mechanical advantage (MA) of a fixed sheave is equal to 1.

3.3  Movable Sheaves: Does not change the direction of the effort force but does increase the size of the force. When you pull on the line, the pulley and the load come up. You can find the mechanical advantage (MA) of a movable pulley by counting the number of lines that lift the load. 3.

3.4  Sheave Systems: These are simply a fixed and movable pulley put together. The sheaves are used to increase the mechanical advantage of the system. A pulley system's mechanical advantage (MA) is equal to the number of supporting ropes.

4  Inclined Planes¹

4.1  The inclined plane is a plane surface set at an angle, other than a right angle, against a horizontal surface. The inclined plane permits one to overcome a large resistance by applying a relatively small force through a longer distance than the load is to be raised.

4.2  A wedge converts motion in one direction into a splitting motion that acts 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.

5  Screw

5.1  A continuous inclined plane (wedge). A screw is a central core with a thread or groove wrapped around it to form a helix. While turning, a screw converts a rotary motion into a forward or backward motion. Screws are generally classified by pitch and thread type, although the shape of the screw head is often used to sort screws too.

Footnotes:

A wedge is really a three dimensional inclined plane. A wedge is just not a right angle.