1. Simple Machines
Unit 2

2. Simple Machines
S8P3. Students will investigate the relationship between force, mass, and the motion of objects.
c. Demonstrate the effect of simple machines (lever, inclined plane, pulley, wedge, screw, and wheel and axle) on work.

3. Work
In science, the word work has a different meaning than you may be familiar with in your everyday life.
The scientific definition of work is:
The transfer of energy when a force moves an object over a distance in the same direction of the force.
Energy: the ability to do work
If no movement happens, no work is done.
Work = force x distance (W = Fd)
Measured in newton-meters or joules (J)
Examples: pushing a shopping cart, turning a door knob, kicking a soccer ball, lifting a box

4. Work or Not Work
A scientist delivers a speech to an audience of his peers. No
A bodybuilder lifts a dumbbell above his head.
Yes
A student pushes against a wall that does not move.
A father pushes a baby in a carriage.
A woman carries a grocery bag to her car.

5. Simple Machines Simple Machine
A device that makes work easier by changing the size and/or the direction of the force used to do the work.
A simple machine does not help you to do less work.
Work with a simple machine = Work without a simple machine
No machine can increase both the magnitude of the force and the distance an object travels at the same time.
Therefore, there is a trade-off between force and distance.

6. Work Work Input (Win) work done on a machine Work Output (Wout)
work done by a machine

7. Win = Wout Win > Wout Work Law of Conservation of Energy
Energy can never be created or destroyed.
Energy can be transformed from one form to another.
You can never get more work out than what you put in.
In an ideal machine...
In a real machine...
some energy (output force) is given off (“lost”) as friction.
Win = Wout
Win > Wout

8. Mechanical Advantage (MA): number of times a machine multiplies the effort force

9. 6 Kinds of Simple Machines
Inclined Plane Family
Inclined Plane
Wedge
Screw
Lever Family
Lever
Pulley
Wheel and Axle

10. How does the Simple Machine Make Work Easier for You?
Inclined Plane
Inclined Plane
A straight, slanted surface used to raise objects because it is higher on one end
Example: Ramps, stairs, ladders
How does the Simple Machine Make Work Easier for You?
The Effects on Work
Mechanical Advantage
Inclined planes: You use less effort force over a longer distance.
The longer the inclined plane = smaller effort force needed = easier work
MA greater than 1 (MA > 1) h l

11. Wedge Wedge A moving inclined plane with 1 or 2 sloping sides
Examples: knives, hatchets, ax blade, blades of scissors, nails, teeth, plow, and chisel
A wedge transfers force in one direction into force in two directions.
Wedges are used to split or cut things apart.

12. How does the Simple Machine Make Work Easier for You?
Screw
Screw
A screw is an inclined plane wrapped around a shaft or cylinder.
Examples: a fastener (screw), jar lid, top of jar, drill bit, light bulb, vise
The inclined plane allows the screw to move itself when rotated.
How does the Simple Machine Make Work Easier for You?
The Effects on Work
Mechanical Advantage
Screws: You use less effort force over a longer distance.
The closer the threads on the screw = longer the inclined plane = smaller effort force needed = easier work
MA greater than 1
(MA > 1)

13. Lever Lever a bar that pivots at a fixed point called a fulcrum
“Give me a place to stand and I will move the Earth.”
– Archimedes
Engraving from Mechanics Magazine, London, 1824
Resistance
arm
Effort arm
Fulcrum

14. The 3 Classes of Levers
The class of a lever is determined by the location of the effort force, the load, and the fulcrum.
Effort force (input force): the force applied to the lever
Load (output/resistance force): the object being moved

15. Lever Mechanical Advantage (MA)
Effort arm length
(input force)
Resistance
arm length
(output force)
Le must be greater than Lr in order to multiply the force.

16. Lever First Class Lever
fulcrum is located between the effort force and resistance force (load)
can increase force, distance, or neither
always changes the direction of force (i.e. a downward effort force on the lever results in an upward movement of the resistance force)
Examples: crowbars, scissors, pliers, tin snips, shovels, and seesaws

17. Lever Second Class Lever
the load (resistance) is located between the fulcrum and the effort force
always increases effort force
does not change the direction of force
effort force moves farther than resistance
When the load is located closer to the fulcrum than to the effort force, an increase in force (mechanical advantage) results.
Examples: nut crackers, wheel barrows, doors, and bottle openers

18. Lever Third Class Lever
the effort force is applied between the fulcrum and the resistance force (load)
always increases the distance that the effort force travels
does not change the direction of force
always produce a gain in speed and distance and a corresponding decrease in force
Examples: arm, tweezers, hammers, baseball bats, brooms, and rakes

19. How does the Simple Machine Make Work Easier for You?
Pulley
Pulley
grooved wheel with a rope or chain running along the groove
a “flexible first-class lever”
a load is attached to one end of the rope and a force is applied to the other end Le F Lr
How does the Simple Machine Make Work Easier for You?
The Effects on Work
Mechanical Advantage
Pulleys: Your effort force changes direction and/or you use less effort force over a longer distance.
Your effort force changes direction = easier work
AND/OR
More pulleys = smaller effort force needed = easier work
MA equal to 1 (MA = 1)
MA greater than 1 (MA > 1)

20. Pulley Mechanical Advantage equal to the number of supporting ropes
MA = 0
MA = 1
MA = 2

21. Pulley Fixed Pulley MA = 1 does not increase force
changes direction of force

22. Pulley
Movable Pulley
MA = 2
increases force
does not change direction

23. Pulley Pulley System/Block & Tackle MA = 4
combination of fixed and movable pulleys
increases force
may or may not change direction

24. Wheel and Axle Wheel Axle Wheel and Axle
two wheels of different sizes that rotate together
the wheel is always larger than the axle
a pair of “rotating levers”
Examples: door knob, gears, car axle, pencil sharpener, screw driver, faucet handles
Wheel
Axle

25. How does the Simple Machine Make Work Easier for You?
Wheel and Axle
When effort is applied to move the wheel, the axle turns a shorter distance, but moves with more force.
The larger the wheel is when compared to the axle, the larger the mechanical advantage.
How does the Simple Machine Make Work Easier for You?
The Effects on Work
Mechanical Advantage
Wheel and Axles: You use less effort force over a longer distance when turning the wheel.
The larger the wheel = smaller effort force needed = easier work
MA greater than 1 (MA > 1)