Simple Machines

Work and Machines A machine is a device

that makes work easier. When you use a

machine, two works are done! The work you do to the machine and the work the machine does to the resistance.

The force you use on the machine is the effort force, and the force opposing your effort (the thing you’re trying to move) is the resistance force.

The distance you move is the effort distance, and the distance the object moves is the resistance distance.

What is Work?

Work is done if (1) an object moves, and (2) if a force acts in the same direction that the object moves.

In other words a Force is applied over a distance. If nothing is moved no work.

Formula for Work Work is done if (1) an

object moves, and (2) if a force acts in the same direction that the object moves.

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

Work is measured in units called Joules (J).

One Joule = 1 kg m2/s2.

Power measures how fast you can do work.

Power = Work / time P = W/t

Solve the Problems

K Box = what you know from the problem (the given values)

F Box = The formula needed

C= calculations (substitute and solve step)

A Box = answer to the problem with all the proper units

How do machines make work easier? The machine reduces

the amount of force you need to use to do work.

The machine may change direction of your effort force so you are pulling in the same direction as gravity.

The machine might reduce the amount you have to push or pull to do the work.

What is a Simple Machine?

A simple machine is a machine that does work with just a small movement.

There are 6 simple machines.

These simple machines can work alone or be combined.

Combining simple machines is called a complex machine.

What are the 6 Simple Machines? The lever is a simple

machine that has 2 parts: a long pole resting on a balancing point. The balancing point is known as a fulcrum.

There are 3 classes of levers depending on where the fulcrum is positioned.

Examples: see-saw, hammer, pliers, broom, arm or leg

Simple Machines - Levers Machines that do work by

moving around a fixed point are called levers.

There are three classes of levers, depending on the location of the fulcrum, effort force, and resistance force (the weight of the load).

The balance point of a lever is called the fulcrum.

The mechanical advantage (M.A.) of a lever can always be found using: M.A.= effort arm length (DE) resistance arm length (DR)

First-class Levers

1st class--The fulcrum is between the effort force and the resistance force in a first class lever.

R

Second class Levers

2nd class--The resistance force is between the effort force and the fulcrum in a second class lever.

R

Third Class Lever

3rd class--The effort force is between the fulcrum and the resistance force in a third class lever.

R

Simple Machines - Pulleys A pulley is a rope wrapped

around a grooved wheel.

The two main types of pulleys are fixed pulleys and moveable pulleys.

To figure out the mechanical advantage of a pulley system, just count the ropes that support the resistance!

Simple Machines - Inclined Planes Simple machines do work

with one movement. There are six kinds of

simple machines: inclined plane, wedge, screw, lever, wheel and axle, and pulley.

A ramp is a inclined plane.

You use less force to pull something heavy up a ramp than you would use if you tried to lift it.

An inclined plane does not make you do less work. It lets you use less effort force, but you have to move a greater distance!

Simple Machines - Wheel and Axle A wheel and axle consists of two circular objects that share the same center.

The larger circle is the wheel and the smaller circle is the axle.

The mechanical advantage of a wheel and axle is the radius of the wheel divided by the radius of the axle.

M. A. = radius of wheel radius of axle

The Wedge A wedge is an inclined plane

that can move. An axe is a wedge, and so is

a chisel, or a wood plane. The effort force used to split wood is great. When you use a wedge, you use less effort force, but move a greater distance.

The Screw A screw is an inclined

plane that is turned in a circle. Car jacks are screws.

You turn a jack handle many times to lift the car a small amount, but the force you need to turn the handle is much less than is needed to lift the car!

Input Work and Output Work

The work you do on the machine is the work input.

Work Input = effort force x input distance

The machine does work on the resistance object. This is called work output.

Work output = resistance force x output distance.

If there is no friction then work input = work output.

If there is friction, work input – friction = work output

Mechanical Advantage Mechanical advantage

tells how many times a machine multiplies your effort force.

Mechanical advantage can also change the direction of your effort force.

M.A. = resistance force

effort force

Mechanical Efficiency Machines make it easier to

do work, but you always put more work into a machine than you get out of it!

This is because some work is used to overcome friction!

Mechanical efficiency (M. E.) of a machine is always less than 100%.

M. E. = work output x 100% work input

Energy and Its Forms Energy can be converted from one form to another.The five main forms of energy are:

Mechanical (sound is included)

Chemical

Nuclear

Electromagnetic (includes electricity, magnetism, and light)

Heat