Section 15-4 : Simple and Compound Machines. Effort Force – force applied to the machine Resistance Force – force the machine tries to overcome. The 6 Simple Machines. Screw. Wedge. Inclined Plane. Pulley. Wheel and Axle. Lever. First Class Lever.
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Effort Force–force applied to the machine
Resistance Force–force the machine tries to overcome
Wheel and Axle
First Class Lever
Fulcrum is between EF (effort) and RF (load)Effort moves farther than Resistance.Multiplies EF and changes its directionThe 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.
RF (load) is between fulcrum and EF Effort moves farther than Resistance.Multiplies EF, but does not change its directionThe 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.
Third Class Lever
EF is between fulcrum and RF (load) Does not multiply force Resistance moves farther than Effort.Multiplies the distance the effort force travelsThe 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
A fixed pulley changes the direction of a force; however, it does not create a mechanical advantage.
Pulley that rises and falls with the load that is being moved
Only changes the Size of the force.
The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley.
Examples: light bulb, jar lid
How do you increase the mechanical advantage of a screw?
Increase the number of threads per inch
Safety Device for Walking on Icy Pavements
When you slip on ice, your foot kicks paddle (A),
lowering finger (B), snapping turtle (C) extends neck
to bite finger, opening ice tongs (D) and dropping pillow (E),
thus allowing you to fall on something soft.