They can change the amount of force They can change the distance (Remember that Work = Force X Distance) They can also change the direction MORE
How do machines make work easier? Any change in the size of the force changes the distance. No machine can increase both force and distance. 1.Multiply force – use a smaller effort force over a longer effort distance 2.Multiply the distance – use a larger effort force over a smaller effort distance 3.Or, they leave force and distance alone but change the direction in which the load moves.
The number of times a machine multiplies the effort or input force. -If MA is greater than 1, the effort force is decreased -If MA is less than 1, the effort distance is decreased -If MA = 1, the direction of the effort is changed
Calculating Mechanical Advantage Ideal MA – does not take friction into account IMA = de/dr effort distance divided by resistance distance MA does not have units Actual MA – takes friction into account AMA = Fr/Fe resistance force divided by effort force
A first class lever is like a teeter-totter or see-saw. One end will lift an object (child) up just as far as the other end is pushed down. A second class lever is like a wheel barrow. The long handles of a wheel barrow are really the long arms of a lever. A third class lever is like a fishing pole. When the pole is given a tug, one end stays still but the other end flips in the air catching the fish. MORE
Diagrams of Levers Effort force = input force Load – output force
Diagrams of Levers http://www.professorbeaker.com/lever_fact.html
Fixed pulley Does not multiply force. Changes the direction of the effort force. Mechanical advantage is equal to one. Movable pulley Multiplies effort force but cannot change direction of the effort force. Mechanical advantage is the effort distance divided by the resistance distance. Pulley system A combination of fixed and movable pulleys. Mechanical advantage is equal to the number of supporting ropes.
A wheel and axle is a modification of a pulley. A wheel is fixed to a axle. The wheel and axle must move together to be a simple machine. Sometimes the wheel has a crank or handle on it. Examples of wheel and axles include roller skates and doorknobs.
Diagram of Wheel & Axle http://www.smartown.com/sp2000/machines2000/wheelandaxle.htm
A simple machine that is a modified inclined plane. The inclined plane wraps around a shaft and is called threads.
Diagram of Screw The closer together the threads on the screw, the longer the effort distance (or inclined plane). A longer inclined plane increases the mechanical advantage.
Go to this link for more information about machines. Remember to hit the “back” button on your browser to return to this slide show. http://www.usoe.k12.ut.us/curr/science/sciber00/8t h/machines/sciber/intro.htm