Simple Machines

What is a Simple Machine? A simple machine

has few or no moving parts.

Simple machines make work easier

Wheels and Axles The wheel and axle

are a simple machine

Gears are a form of wheels and axles

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

Inclined Planes An inclined plane is

a flat surface that is higher on one end

Inclined planes make the work of moving things easier

Wedges Two inclined

planes joined back to back.

Wedges are used to split things.

Screws A screw is an

inclined plane wrapped around a shaft or cylinder.

The inclined plane allows the screw to move itself when rotated.

Levers-First Class In a first class lever

the fulcrum is in the middle and the load and effort is on either side

Think of a see-saw

Levers-Second Class In a second class

lever the fulcrum is at the end, with the load in the middle

Think of a wheelbarrow

Levers-Third Class In a third class lever

the fulcrum is again at the end, but the effort is in the middle

Think of a pair of tweezers

Simple Machines Simple Machines

can be put together in different ways to make complex machinery

Simple Machines- Mechanical AdvantageMechanical advantage (MA) is the ratio

of the force put into the machine (Effort Force) to the force the machine exerts on an object (Resistance Force).

MA = Fr / Fe MA > 1 means that the machine makes

work easier and increases the amount of force applied

A sample problemA worker uses a pulley to lift a 45 kg

object. If the mechanical advantage of the pulley is 5.2, what is the effort force exerted by the worker?

MA = Fr / Fe

Effort Force = ???Mass = 45 kgResistance Force = 45 * 9.8 = 441 N

5.2 = 441 N / Fe

Effort Force = 85 N

A sample problem – You try itA worker uses a lever to lift an object

with a mass of 3500 N. If the force applied by the operate was 1500 N, what is the mechanical advantage of the lever?

MA = Fr / Fe Effort Force = 1500 NResistance Force = 3500 N

MA = 3500 N / 1500 N

MA = 2.33

Simple Machines – Ideal Mechanical Advantage Ideal Mechanical advantage is the ratio

of distance moved by the person (de ) to the distance the machine moved the object (dr ).

IMA = de / dr

LOOK AT PAGE 266 Figure 10-9

A Sample Problem- You Try itA worker testing a multiple pulley

system to estimate the heaviest object the system could move. When the worker moves the rope 1.5 m, the object moves 0.25 m. What is the IMA of the system?

IMA = de / dr

Simple Machines - efficiencyEfficiency is the ratio of work output

(Wo) to work input (Wi ) multiplied by 100. Efficiency = e = (Wo / Wi ) *100

Another way to calculate it using mechanical and ideal mechanical advantage Efficiency = e = (MA / IMA) * 100

A sample problem

A man exerts a force of 310 N on a lever to raise a crate with a mass of 910 kg. If the efficiency of the lever is 78%, what is the lever’s IMA?e = (MA / IMA) * 100 IMA = de / dr MA = Fr / Fe

Effort Force = 310 NMass = 910 kgResistance Force = 910 * 9.8 = 8910 N

MA = 8910 / 310MA = 28.7

e = (MA / IMA) * 100

78 = (28.7 / IMA) *100

IMA = 36.8

A sample problem – You Try It

A man exerts a force of 650 N on a lever to raise a crate with a weight of 1000 N. If the efficiency of the lever is 55%, what is the lever’s IMA?e = (MA / IMA) * 100 IMA = de / dr MA = Fr / Fe

Effort Force = 650 NResistance Force = 1000 N

MA = 1000 / 650MA = 1.53

e = (MA / IMA) * 100

55 = (1.53 / IMA) *100

IMA = 2.8

HomeworkPage 280

Problems: 79-84