Physics!Simple Machines!

What is work?

•When you exert a force on an object that causes it to move some distance

•Work=Force x Distance

Mechanical Advantage

•mechanical advantage (MA) is the factor by which a mechanism multiplies the force or torque applied to it.

Calculating Mechanical Advantage•MA = distance over which force is

applied/ distance over which load is moved

•MA = output force/input force

Inclined Plane

•A flat sloped surface•How it works: exert a force over a longer

distance•Mechanical Advantage: divide length of

incline by its height▫I MA = LI/HI

3

1

Inclined Plane

•When is this an advantage?▫Using a ramp versus lifting straight up▫Begin the motion of an object

Input force

Output force

Wedge

•Thick at one end and tapers to a thin end at the other

•How it works: move the inclined plane, turns the output force at a 90 degree angle

•Mechanical advantage: divide the length of the wedge by its width▫W MA = Wl/WW

5

4

WedgeInput force

Output force

Output force

Screw

•Inclined plane wrapped around a cylinder•How it works: Threads increase the

distance over which you exert the input force. Output force pulls screw into object

•Mechanical Advantage: the closer the threads the greater the MA.▫S MA = length around threads/ length of

screw

Screw

Output force

Lever

•Bar over a fulcrum•How it works: input force, pivots on the

fulcrum, output force•Mechanical Advantage: distance to input

force/distance to output force▫L MA = D IF/D OF

FulcrumOutput force (dist)

Input force (distance)

Levers

Fulcrum

Input force (longer dist)

Output force (dist)

Types of Levers• 1st Class Lever – Change the direction of

input force. The fulcrum is between the output force and input force.

• Examples: scissors, pliers, seesaw• 2nd Class Lever – increase the force, they

don’t change the direction of the force.• Examples: door, nutcracker, bottle opener• 3rd Class Lever – increase distance, don’t

change direction.• Examples: Fishing pole, shovel, baseball bat

 

Wheel & Axle•Two cylindrical objects fastened together and rotate on a common axis. Large radius is the wheel, small radius is the axle.

•How it works: Increases force, must exert force over a longer distance

•Mechanical Advantage: radius of wheel/radius of axle▫WA MA = RW/RA

R = 5

R = 0.5

Wheel & Axle

Output force

Input force

Pulley

•A grooved wheel with a rope or cable•How it works: increase the effect of your

input force. Changes the direction of the input force.

•Mechanical Advantage: number of sections of rope that support the object

Input forceOutput force

Pulley

•Fixed pulley – does not change the amount of force applied, only changes direction

•Moveable pulley – increase amount of force applied, does not change direction

•Block and tackle – both fixed and moveable pulleys