1. Work and Simple Machines
All you need to know about simple machines

2. Work Work is when a force is exerted on an object causing it to move.
*If an object doesn’t move, NO work is done.
*The force must be in the same direction the object moves. (If you carry something it is NOT work because the force is up & the movement is horizontal).

3. Work (cont.) Formula : Work = Force X Distance
Measured in Newton meters (Nm) or Joules (J) (Named after physicist James Joule)
1 Joule = 1 Nm
Sample problem:
If you use 20 N of force to move a desk 10 m how much work is done?
Solution:
Work = F X D
Work = 20 N X 10 m
(D)
Work = 200 Nm or 200 J

4. What is a machine?
A machine is any device that makes work easier or transfers energy.
A machine makes work easier 3 ways.
Changing force exerted amount
Changing distance you exert force
Changing direction you exert force
*Input force – force you exert on the machine
*Output force (resistance force) – force exerted by the machine.

5. Mechanical Advantage Mechanical advantage = output force / input force
If the mechanical advantage is greater than 1 it multiplies force.
If the mechanical advantage is less than 1 it multiplies distance
If the mechanical advantage = 1 it changes direction.

6. Efficiency
Efficiency is used to see how good a machine is & how much work is wasted overcoming outside forces like friction or tools that stick.
*Efficiency = output work / input work X 100%
Ideal mechanical advantage – how the machine would work without friction.
Actual mechanical advantage – the actual advantage of a machine including friction.
Sample problem:
You go out to cut grass with a non motorized push lawn mower. You put 250,000 J of work into mowing the work done by the mower is 200,000 J what is the mower’s efficiency?
Solution
Efficiency = output work / input work X 100%
Efficiency = 200,000 J / 250,000 J X 100%
.8 X 100% = 80%
The lawn mower is 80% efficient.

7. Simple Machines There are 6 basic kinds of simple machines.
Inclined plane
Wedge
Screw
Lever
Wheel & Axle
Pulley

8. Inclined Planes
Inclined planes – a flat slanted surface like a ramp. It allows you to exert your input force over a longer distance.
*The longer the inclined plane the greater the mechanical advantage if your planes height doesn’t change.

9. Wedges Wedge – 1 or 2 moving inclined planes.
An axe head & a zipper are examples of wedges.
It multiplies the force to do more work

10. Screws Screw- an inclined plane wrapped around a cylinder
The closer the threads of a screw the greater the mechanical advantage.

11. Levers The fixed point is called a fulcrum.
Lever- a rigid bar that moves around a fixed point.
The fixed point is called a fulcrum.
There are 3 classes of levers
1st class- multiplies forces or distance depending on fulcrum placement. Also changes input force direction. Ex. Scissors, pliers, seesaws.
2nd class- multiplies forces but don’t change direction of input force. Ex. Wheelbarrows, doors, bottle openers, nutcrackers.
3rd class - multiplies distance but doesn’t change input force direction. Ex. Fishing poles, baseball bats, shovels.
The mechanical advantage is greater than 1 if the fulcrum is farther from the input force but you can move it a shorter distance.

12. Wheel & Axle
Wheel & Axle – 2 cylinders stuck together that rotate about a common axis.
The larger (in diameter) cylinder is the wheel
The smaller (in diameter) cylinder is the axle.
Ex. Doorknobs, screwdrivers, vehicles.

13. Pulley
Pulley – a grooved wheel with a rope, chain, etc. wrapped around it to pull other objects with.
You change the amount & direction of the input force
Pulley types:
Fixed pulleys – change direction but not amount of force. Mechanical advantage (MA) = 1.
Movable pulleys – change amount of input force. MA = 2.
Pulley systems – also called “block & tackle”
The ideal mechanical advantage of a pulley system is = the number of sections that support the weight.

14. Compound Machines
A compound machine is a machine that uses 2 or more simple machines.
To calculate the MA of a compound machine you must calculate the MA of each simple machine in it & add them together.
Ex. Pencil sharpener (Wheel & axle & screws).
Gears are toothed wheels that fit together to help turn other objects. (They connect wheels & Axles to each other.)

15. Machines in the Human Body
Many body parts act like simple machines & help the body do work.
Muscles & tendons act like levers.
Teeth act like wedges.