THE INCLINED PLANE FAMILY

Inclined planes, wedges,

and screws

INCLINED PLANES An inclined plane is the simplest

of the simple machines because there are no moving parts.

A plane is a flat surface, and if it is inclined, one end of it is raised.

Examples include ramps, sloped roads or driveways, and the up or down sections of a roller coaster.

M.A. OF INCLINED PLANE The inclined plane produces a mechanical advantage

by increasing the distance a force must move. The box below is moved 15 feet along the slope in

order to increase the vertical distance (height) by 3 feet.

M.A. OF INCLINED PLANE The mechanical advantage of an

inclined plane is equal to the length of the slope divided by the height of the inclined plane.

MA = Slope/Height

FORCE – INCLINED PLANE As the angle of incline increases, the

force required to move the blocks at constant speed increases too.

Imagine that you need to move a block to the top of a table.

Block C illustrates that you must exert the greatest force to lift the block to the table top when the angle in incline is the greatest.

For block B, the distance through which you exert the force is the shortest.

For block A, you would exert less force in the first example, but would need to exert that force over a greater distance.

A B C

TRADE-OFFS

WEDGE Examples of wedges are everywhere in

your life: knives, nails, fork tines, flat head screwdrivers, ax heads, your front teeth (incisors)

Now imagine a wedge (perhaps an axe) on the top of the block of wood. You hit the top of the wedge with a hammer.

Imagine holding a block of wood and trying to pull it apart into two pieces. That would be difficult…

WEDGE DEFINITION A wedge is two

inclined planes placed back-to-back.

A wedge allows you to push through and cut apart substances with less force than you would need to push through or pull the substance apart without the wedge.

Incl

ined P

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#1

Inclin

ed P

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#2

HOW WEDGES WORK The force of the hammer is in a

downward direction. The wedge changes the direction of the force outward, pushing sections of the block apart.

WEDGE EXAMPLE A knife cutting butter functions the

same way. You push downward on top of the putter with a knife.

The butter is not crushed under the edge of the knife, it is pushed apart into two pieces as the knife moves through it.

M.A. OF A WEDGE The mechanical advantage of a wedge

is determined by dividing the length of the slope (S) by the thickness (T) of the widest end.

M.A. OF A WEDGE In the example below, the length of the

slope of the wedge is 6 inches and the thickness is 2 inches.

The mechanical advantageis equal to 6/2, or 3.

SCREW A screw is a

combination of simple machines: it’s an inclined plane that wraps around a shaft with a wedge at the end of the shaft.

Some screws are used to lower and raise things.  They are also used to hold objects together.

EXAMPLES OF SCREWS Jar Lids Light Bulbs Stools Clamps

Jacks Wrenches Key Rings Spiral Staircase

MA OF SCREW The total mechanical

advantage of a screw is equal to the circumference of the screwdriver handle divided by the pitch of the screw. (The pitch is the distance from one thread to the next.)

MA OF SCREW In this example, a screw with

12 threads per inch is turned by a screwdriver having a handle with a diameter of 1.5 inches.

MA = Handle circumference/PitchHandle circumference = 1.5 x Pi

= 1.5 x 3.14 = 4.71”Pitch = 1/12 of an inch = 0.083”

MA = 4.71”/0.083” = 56.7

SCREWS - PITCH The screw with more

space between thread (higher pitch) will take more force and less turns to be turned into the wood.

The screw with less space between threads (lower pitch) will take less force and more turns to be turned into the wood.