Simple Machines

Biblical Reference

The wheels were made like chariot wheels; the axles, rims, spokes and hubs were all of cast metal.

1 Kings 7:33

What is a Simple Machine?• A simple machine has few or no moving

parts.• Simple machines make work easier.• Simple Machines:

– Transfer a force from one place to another.

– Change the direction of a force.

– Increase the distance or speed of a force.

What is a Simple Machine?• Six types of simple machines do work

using only one movement.

• Lever

• Wheel and Axle

• Inclined Plane

• Wedge

• Screw

• Pulley

Levers• A lever is a rigid bar that

rotates around a fixed point, called the fulcrum.– The bar can be either

straight or curved.

• Force is applied at one end of a lever, and the force is transferred to a load at the other end.

Three Classes of Levers• The class of a lever is determined by the

location of the applied force and the load in relation to the fulcrum.

First Class Levers• In a first-class lever,

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

• The direction of the input force is opposite the direction of the output force

First Class Levers• A finger tab on a beverage can is a first-

class lever.

Second Class Levers• A second-class lever

has the output force between the input force and the fulcrum.

• The output force and the input force act in the same direction.

• A second-class lever makes the output force greater than the input force.

Second Class Levers• A wheel barrow is an example of a

second-class lever.

Third Class Levers• A third-class lever

has the input between the output force and the fulcrum.

• The output force is less than the input force. Both the input force and the output force act in the same direction.

Third Class Levers• A rake is an example of a third-class lever.

Levers on the Human Body• The neck, foot, and arm are examples of

first-, second-, and third-class levers in the human body..

Mechanical Advantage of Levers• The ideal mechanical advantage of a lever

equals the length of the input arm divided by the length of the output arm.

1st Class Lever MA

2nd Class Lever MA

3rd Class Lever MA

Wheel & Axle• The wheel and axle

are a simple machine.

• The axle is a rod that goes through the wheel which allows the wheel to turn.

• Gears are a form of wheels and axles

Wheel & Axle• For a wheel & axle, the length of the input

arm is the radius of the wheel; the length of the output arm is the radius of the axle.

• A screwdriver is a wheel & axle. The handle is the wheel and the shaft is the axle.

Wheel & Axle MA• Even though no machine is 100% efficient,

you can calculate the ideal mechanical advantage of a wheel and axle.

Inclined Planes• An inclined plane is a flat

surface that is higher on one end

• Inclined planes make the work of moving things easier– Can be used to change effort

and distance involved in doing work.

Inclined Planes• Moving a sofa is easier using a ramp.

– Using a ramp only requires a 100-N force to move the 500-N sofa.

– Because of friction, no ramp operates at its ideal mechanical advantage.

Inclined Plane MA• The ideal mechanical advantage of an inclined

plane equals its length divided by its height.

Inclined Planes• The longer or less-

sloped an inclined plane is, the less force is needed to move an object along its surface.– A wagon train often went back

and forth up a steep hill to reduce the slope to help a team pull a heavy load

– This same technique is used in modern freeways, which travel winding paths up steep mountains

Wedge• A sloped surface that

moves is called a wedge.• A wedge is really a type

of inclined plane with one or two sloping sides.– The MA of a Wedge is

the length of either slope divided by the thickness of the big end.

Screw• A screw is an inclined

plane wrapped around a cylinder.– The inclined plane allows

the screw to move itself when rotated.

– When you turn a screw, the screw threads change the input force to an output force and the output force pulls the screw into the material.

Screw MA• The MA for a screw is the number of

threads per linear inch.

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 pulley can be used to change the direction of a force or gain mechanical advantage.

Fixed Pulley• A fixed pulley only

changes the direction of the force.

Movable Pulley• Movable pulleys are

attached to the object being lifted and decrease the force needed to lift the object.

Pulley System• A pulley system is a

combination of fixed and movable pulleys that work together.

Pulley MA• The ideal mechanical

advantage of a pulley or a pulley system is equal to the number of sections of rope supporting the object.

Compound Machines• Simple Machines can be

put together in different ways to make complex machinery.– Compound Machines

can be as small as a watch or large as a tank.

Gears• A gear is a wheel and axle with teeth

around the wheel. – Two or more gears working together form

a compound machine.– When the teeth of two gears interlock, turning

one gear causes the other to turn.– Gears of different sizes turn at different speeds.

Compound Machine Efficiency• The efficiency of a compound machine is

calculated by multiplying the efficiencies of each simple machine together.– Each simple machine decreases the overall

efficiency of the compound machine.

Example: Wheel & Axle (93%), Screw (88%), Lever (91%) & Wedge (96%)

%5.71%100)96.0)(91.0)(88.0)(93.0( TotEff

Everyday Compound Machines

Everyday Compound Machines

A. Complex Machines

B. Compound Machines

C. Ideal Machines

D. Simple Machines

What are levers, wheels and axles, inclined planes, wedges, screws, and pulleys examples of?

Pop Quiz

Which uses less force to raise an object compared to lifting the object straight up?

Pop Quiz

A. Fulcrum

B. Inclined plane

C. Screw

D. Wheel

Which is a simple machine consisting of a grooved wheel with a rope or cable wrapped around it?

Pop Quiz

A. Gear

B. Pulley

C. Screw

D. Wedge