Chapter 5: Work and Machines

 Describe the six types of simple machines.  Explain how the different types of simple machines make work easier.  Calculate mechanical advantage.

 Simple Machine: a machine that does work with only one movement of the machine.

 Lever: a rigid bar that rotates around a fixed point called the fulcrum.  The bar may be either independent or attached to another object.

 In use, a lever has both an input force and an output force.

Input Force Output Force

 First Class Lever: fulcrum is in the middle of the input and output forces  MA may be greater or less than 1  Ex: scissors, see-saw, crowbar

Input Force Output Force

 Second Class Lever: output force is in-between the input force and the fulcrum.  MA is always greater than 1  Ex: wheelbarrow, nut cracker, bottle opener

Input Force Output Force

 Third Class Lever: input force is in-between the output force and the fulcrum.  MA is always less than 1  Ex: tweezers, staple remover, broom

 Pulley: a machine that consists of a wheel that turns freely in a frame called a block.

 A pulley can be used to change the direction of a force or to increase input force depending on how the pulley is arranged.

 Fixed Pulley: changes the direction of a force; however it does not create a mechanical advantage.  Example: Elevator

 A single moveable pulley creates a mechanical advantage; however it does not change the direction of a force.

 The mechanical advantage of a moveable pulley is equal to the ropes that support the moveable pulley.

 Wheel and Axle: a simple machine consisting of a larger wheel rigidly secured to a smaller wheel or shaft, called an axle.

 When either the wheel or axle turns, the other rotates with it.  One full revolution of either part causes one full revolution of the other part.

 Examples:  Pencil sharpener  Door knob  Faucet handles

 Inclined plane: is a sloping surface that reduces the amount of force required to do work by increasing the distance over which work is done.  The inclined plane makes it easier to move a weight from a low height to a high height.

 Wedge: an inclined plane that has one or two sloping sides.  It changes the direction of the input force.

 Examples:  Knife/ax  Door stopper

 Screw: an inclined plane wrapped in a spiral around a post.  The threads form a tiny ramp that run upward from its end.

 Example:  Many types of lids  Screws

 Two or more simple machines operating together.