What are they? Simple machines are machines with few or no moving parts that are used to make work easier
Energy: Ability to do work Work= Force x Distance Force: A Push or a Pull Definitions:
Why Use Simple Machines? For the mechanical advantage… Making something easier to do, but it takes a little longer to do it For example, going up a longer flight of stairs instead of going straight up a ladder
The 6 Simple Machines Lever Pulley Wheel and Axle WedgeScrew Inclined Plane
The mechanical advantage of a lever is the ratio of the length of the lever on the applied force side of the fulcrum to the length of the lever on the resistance force side of the fulcrum.
Fulcrum is between EF (effort) and RF (load) Effort moves farther than Resistance. Multiplies EF and changes its direction First Class Lever
Group Discussion What are 3 examples of first class levers?
First Class Lever. – Common examples of first-class levers include crowbars, scissors, pliers, tin snips and seesaws.
RF (load) is between fulcrum and EF Effort moves farther than Resistance. Multiplies EF, but does not change its direction The mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance from the resistance force to the fulcrum. Second Class Lever
Second Class Lever Examples of second-class levers include nut crackers, wheel barrows, doors, and bottle openers.
EF is between fulcrum and RF (load) Does not multiply force Resistance moves farther than Effort. Multiplies the distance the effort force travels The mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance of the resistance force to the fulcrum Third Class Lever
Third Class Lever Examples of third-class levers include tweezers, arm hammers, and shovels.
Wheel and Axle Group: What are 3 complex machines that use wheel and axles?
Wheel and Axle Makes it easy to move things by rolling them, and reducing friction Examples: car, bicycle, office chair, wheel barrow, shopping cart, hand truck, roller skates
Wheel and Axel The mechanical advantage of a wheel and axle is the ratio of the radius of the wheel to the radius of the axle. MA = Rwheel / Raxle In the wheel and axle illustrated above, the radius of the wheel is five times larger than the radius of the axle. Therefore, the mechanical advantage is 5:1 or 5. 5 1
The wheel and axle can also increase speed by applying the input force to the axle rather than a wheel. This increase is computed like mechanical advantage. This combination would increase the speed 5 times.
Pulley Makes lifting things with a rope easier by redirecting force and the addition of additional pulleys Examples: flag pole, elevator, sails, fishing nets, clothes lines, cranes, window shades and blinds, rock climbing gear
Pulleys Pulley are wheels and axles with a groove around the outside A pulley needs a rope, chain or belt around the groove to make it do work
A fixed pulley does not create a mechanical advantage. It only allows you to change the direction of force.
Moveable Pulley A moveable pulley has a mechanical advantage of 2n (n = number of moveable pulleys).
Wedges Two inclined planes joined back to back. Wedges are used to split things.
Wedge – Mechanical Advantage The mechanical advantage of a wedge can be found by dividing the length of either slope (S) by the thickness (T) of the big end. S As an example, assume that the length of the slope is 10 inches and the thickness is 4 inches. The mechanical advantage is equal to 10/4 or 2 1/2. As with the inclined plane, the mechanical advantage gained by using a wedge requires a corresponding increase in distance. T
Wedge Pushes materials apart, cuts things Examples: axe, doorstop, chisel, nail, saw, jackhammer, bulldozer, snow plow, horse plow, zipper, scissors, airplane wing, knife, fork, bow of a boat or ship
36 Screw The screw is also a modified version of the inclined plane. While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp (or inclined plane).
37 MA of an screw can be calculated by dividing the number of turns per inch.
Screw Turns rotation into lengthwise movement Takes many twists to go a short distance Holds things together Examples: screws, bolts, clamps, jar lids, car jack, spinning stools, spiral staircases
Mechanical Advantage of the Screw MA = π x d / L L = distance between the threads D = the diameter of the cylinder
Practice Problems 1. First Class Lever: The Effort length is 12m. The Load length is 3m. What is the mechanical advantage?
2. Wheel and Axle The wheel has a radius of 15 cm. The axle has a radius of 2 cm. That is the mechanical advantage?
3. Inclined plane An inclined plane has a length of 18m. The plane has a height of 6m. What is the mechanical advantage?
4. Pulleys A single fixed pulley with a rope 8ft long is used to life 18N. What is the mechanical advantage?