Power and Energy Technology Simple Machines Power and Energy Technology
Behavioral Objectives Students will gain an understanding and be able to identify and use all of the following: Six Simple Machines Four classes of levers Pulleys Fixed Movable Block and Tackle Wheels and Axles Gears Types Bicycle applet
Incline Plane A surface set to an angle to another surface Same amount of work just over a longer distance Resistance Force Inclined Plane
The Wedge Double incline plane Pushes two objects apart Force Effort
The Screw A screw is a shaft that has a in inclined groove along its surface. By rotating the screw (applying a torque), the force is applied perpendicular to the groove, thus translating a rotational force into a linear one. Babylonians developed a "screw" that could elevate water from a low-lying body to a higher one (which later came to be known as Archimedes' screw).
Archimedes' screw
Wheels and Axles Type of lever that rotates around a center fulcrum. Force applied to provide rotation on the axle translates into rotation of the wheel. Force applied to the wheel causes the axle to rotate, which can be used to magnify the force (by, for example, having a rope wind around the axle).
The Lever Consists of a rigid object (bar of some kind) and a fulcrum (Pivot) There are three classes of lever Each offer magnification of the force at another point along the rigid object.
Load Fulcrum First Class Lever Effort
Second Class Lever Effort Fulcrum Load
Third Class Lever Load Fulcrum Effort
Pulleys A wheel with a groove along its edge, where a rope or cable can be placed. principle of applying force over a longer distance Provides mechanical advantage
Fixed Pulley Offers no mechanical Advantage Changes direction of force
Movable Pulley Block and Tackle Combination of fixed and a movable pulleys Can have several pulleys mounted on the fixed and moving axles, further increasing the mechanical advantage.
Block and Tackle Pulleys are assembled together to form blocks Blocks are paired so that one is fixed and one moves with the load A single rope is threaded, or reeved, through the pulleys to provide mechanical advantage
Types of Block and Tackle
Gun Tackle
Double tackle
Gears Are used to change speed, direction and torque Basic gears Spur Gear Bevel Gear Worm Gear Rack and Pinion
Spur Gear Straight-cut gears are the simplest type of gear Gears can be meshed together correctly only if they are fitted to parallel shafts.
Bevel Gear Creates right angles Changes direction of movement
Worm Gear High torque, low speed gear ratio Can create continuous motion
Rack and Pinion Toothed bar or rod. Torque can be converted to linear force by meshing a rack with a pinion: the pinion turns; the rack moves in a straight line
Gear Ratios http://illuminations.nctm.org/ActivityDetail.a spx?ID=178 Gear up this bicycle for speed or power.