Simple Machines
Subpages (8): Cam Gear Inclined Plane Levers Pulley Screw Wedge Wheel & Axle
Mechanical systems produce and/or then control forces in order to create desired output motion. Simple machines make it easier to do mechanical work by providing mechanical advantage. Mechanical advantage is a mathematical calculation of how much easier a mechanical system make doing work. There are three kinds of advantages that simple machines can provide. They can produce a force multiplication (greater out force), produce a distance/speed multiplication (force applied over a greater distance) or simple change the direction of a force or motion.
Kinds of Simple Machines
The two most basic simple machines are levers and inclined planes. Levers reverse direction of a force (you push down and the load goes up). Inclined planes create an output motion that is perpendicular to the input motion (you push horizontally and the load moves up). A wedge is just an inclined plane that moves. If you design a lever to rotate all the way around (360 degrees) you will have a wheel and axle. A wheel with a grove around its circumference is a pulley. Add teeth to the edge of a wheel and you have a gear. The axles of the wheel & axle, the pulley and the gear are the point that the motion rotates about and are equivalent to the fulcrum of the lever. The screw and cam are combinations of the concept of lever and inclined plane. A screw has an inclined plane wrapped around an axle. A cam has an inclined plane added to a wheel. In both an rotary input motion produces a linear output motion.
Inclined Plane - A sloping ramp up where heavy loads can be raised.
Wedge Tool- Triangular shaped tool, used to separate, lift up, or hold an object.
Lever
Lever Arm- - The lever arm is defined as the perpendicular distance from the axis of rotation to the line of action of the force.
Mechanical Advantage = Effort Arm / Load Arm
Classes of Levers:
Class 1: Fulcrum is directly in the middle, the effort is applied on one side of the fulcrum and the resistance (or load) on the other side, for example, a seesaw, a crowbar or a pair of scissors.
Class 2: Resistance (or load) in the middle: the effort is applied on one side of the resistance and the fulcrum is located on the other side, for example, a wheelbarrow, a nutcracker, a bottle opener or the brake pedal of a car. Mechanical advantage is always greater than 1.
Class 3: Effort in the middle: the resistance (or load) is on one side of the effort and the fulcrum is located on the other side, for example, a pair of tweezers or the human mandible. Mechanical advantage is always less than 1.
Wheel- a circular object that revolves on an axle and is fixed below a vehicle or other object to enable it to move easily over the ground.
Wheel & Axle- A simple lifting machine consisting of a rope that unwinds from a wheel onto a cylindrical drum or shaft joined to the wheel to provide mechanical advantage.
Pulley- a wheel with a grooved rim around which a cord passes. It acts to change the direction of a force applied to the cord and is chiefly used (typically in combination) to raise heavy weights.
Mechanical Advantage = number of rope sections parallel to the output motion
Screw- A short, slender, sharp-pointed metal pin with a raised helical thread running around it and a slotted head, used to join things together by being rotated so that it pierces wood or other material and is held tightly in place. Different types of screws: Pan head, Flat head, Round head, Oval head, Fillister head, Binding head, Truss head, Holt head, One-Way head.
Gear- one of a set of toothed wheels that work together to alter the relation between the speed of a driving mechanism (such as the engine of a vehicle or the crank of a bicycle) and the speed of the driven parts (the wheels).
Mechanical Advantage = Input teeth / Output teeth
Cam- a projection on a rotating part in machinery, designed to make sliding contact with another part while rotating and to impart reciprocal or variable motion to it.