Simple Machines and Work

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

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

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 A lever is a simple

machine containing a bar that can turn around a fixed point

Fixed point is called a fulcrum

There are three classes of levers

Levers The force the person applies to the

machine is called effort force The object to be lifted, the load, is called

the resistance. The force the machine uses to move the

resistance is called the resistance force The force the machine exerts is greater

than the force the person exerts, SO using a machine makes a person’s job easier!

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 and Work Energy cannot be created or destroyed;

and, because energy is the ability to do work, work cannot be created either

No simple machine can do more work than the person using it supplies

Machines can increase or change the direction of the force a person exerts; and, some machines allow a person to use less force to do the same amount of work

Simple Machines and Work The amount of work a person puts into a machine is

called the work input Work input equals the person’s effort force

multiplied by the distance of that effort work input = fe × de

The amount of work actually done by the machine against the resistance is called the work output

Work output equals the resistance force multiplied by the distance the resistance moved

work output = fr × dr

Simple Machines and Work Work output can never be greater than work input

because energy cannot be created The efficiency of a machine measures how much

useful work it can do compared with how much work was put into it

efficiency = work output/work input × 100%

Efficiency is written as a percent, and multiplying by 100 tells you what percent of the work input is converted to work output

ALL machines have efficiencies that are less than 100 percent

Mechanical AdvantageA simple machine makes a task easier

because it multiplies the force a person applies

The number of times a machine multiples your effort force is called the mechanical advantage

mechanical advantage = resistance force /effort force

Mechanical AdvantageSuppose a machine lifts a resistance

that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage?

MA = Fr/Fe MA = 30 newtons/10 newtons

MA = 3

Mechanical AdvantageSuppose a machine lifts a resistance

that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage?

MA = Fr/Fe MA = 30 newtons/10 newtons

MA = 3

Mechanical AdvantageSuppose a machine lifts a resistance

that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage?

MA = Fr/Fe MA = 30 newtons/10 newtons

MA = 3

Mechanical AdvantageSuppose a machine lifts a resistance

that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage?

MA = Fr/Fe MA = 30 newtons/10 newtons

MA = 3

Mechanical Advantage You can increase the mechanical advantage

of a lever simply by moving the fulcrum closer to the resistance and farther from the effort force

The effort arm is the distance between the fulcrum and the effort force of a lever

The resistance arm is the distance between the fulcrum and the resistance force of a lever

MA = effort arm/resistance arm

Mechanical Advantage To increase Mechanical Advantage in a

pulley, simply add more pulleys For each pulley the

MA is 1