How Machines do Work

Mechanical Advantage and Efficiency

What is a Machine?

0 Shovel0 Wheelbarrow0 Bulldozer0 Rake

What is a Machine?

0A machine is a device that makes work easier!0Amount of work does

not change!

2 Types of MachinesSimple

0Unpowered mechanical device0There are 6:

0Lever0Pulley

0Wheel and Axle0 Incline Plane

0Screw0Wedge

Compound0A machine that has two or

more simple machines

Input Force0The force YOU PUT INTO the machine is called the

input force.

0It is also called the EFFORT force

0In other words: The input includes everything you do to make the machine work.

Input Force

Output Force0The force done by the machine is called the

output force.

0Also called the RESISTANCE

0In other words: The output is what the machine does for you.

Output Force

Force/Distance Trade Off0Mechanical Advantage: how many times the

machine increases your force 0(how much the machine makes work easier)

0A machine can make work easier by changing either:0Direction0Distance 0Force

0The amount of work stays the same!!

Changing Direction0When a machine changes the direction of the

input force, the amount of force and distance remain the same

InputDirection

Output Direction

Changing Distance0If you want the machine to increase your distance,

you must apply more force over a shorter distance.

0Force (F) x distance (d) = Work (W) = Force (F) x distance (d)Input Distance

OutputDistance

Changing Force0 If you want the machine to help you use less

force, you must apply the smaller force over a longer distance.

0Force (F) x distance (d) = Work (W) = Force (F) x distance (d)

Efficiency of Machines

0The efficiency of a machine tells how well the machine works

0Efficiency is always a percent.

0The higher the percent, the more efficient the machine is.090%075%050%

Input and Output Work0Friction always converts some of the input work to heat

and wear, so the output work is always less than the input work.

0The more friction in a machine, the less efficient the machine!

More

Less

Real vs. Ideal Machines0An ideal machine would have an efficiency of 100%.

0However, all real machines have an efficiency of less than 100% because some work is wasted due to friction.