1. MACHINES

2. Simple Machines A device that does work in one movement
Makes work easier by changing the force you exert in size, direction, or both

3. Applying Force and Doing Work
Two forces are involved when a machine is used to do work
The force applied to the machine is called the effort force (Fe)

4. Applying Force and doing Work
The force applied by the machine to overcome resistance is called the resistance force (Fr)

5. Work
There are two kinds of work to be considered when a machine is used
The work done on the machine or work input (Win)
The work done by the machine or work output (Wout)

6. Work Work is the product of force and distance: W = F x d
Work input is the product of the effort force and and the distance that force is exerted
Win = Fe x de
Work output is the product of the resistance force and the distance that force is exerted
Wout = Fr x dr

7. Energy is always conserved (There is no free lunch)
You can never get more work out of a machine than you put in
Wout = win
In fact Wout is always smaller then Win due to energy loss due to friction

8. The Perfect Machine
Although a perfect machine has never been built, it helps to imagine a frictionless machine in which no energy is converted to heat
Win = Wout
Fe x de = Fr x dr

9. Mechanical Advantage
The number of times a machine multiplies the effort force is the mechanical advantage (MA)
MA = resistance force
effort force
MA = Fr Fe

10. Levers
A lever is a bar that is free to pivot on a fixed point which is called a fulcrum
The part of the lever on which the effort force is applied is the effort arm
The part that exerts the resistance force is called the resistance arm

11. Levers IMA = length of effort arm
A lever makes work easier by multiplying your effort force and changing the direction of your force
The ideal mechanical advantage can be found by dividing the length of the effort arm by the length of the resistance arm
IMA = length of effort arm
length of resistance arm

12. Types of Levers

13. Types of Levers
There are three types of levers that are based on the position of the effort force, resistance force, and the fulcrum
The easiest way to remember them is to just remember what is in the middle
1st class – fulcrum
2nd class – resistance
3rd class – effort
FRE

15. Pulleys
A pulley is a grooved wheel with a rope or chain running along the grove
A pulley works like a 1st class lever, instead of a bar it has a rope, the axle works as the fulcrum. The two sides of the pulley are the effort and resistance arms

16. Pulleys Pulleys can be fixed or movable
A fixed pulley is attached to something that doesn’t move and can change the direction of an effort force, it does not multiply the effort force
A fixed pulley will have a mechanical advantage of one

17. Pulleys A movable pulley multiplies the effort force
A movable pulley will have a mechanical advantage greater than one
A single movable pulley will have a ideal mechanical advantage of 2

18. Block and Tackle
A block and tackle is a combination of fixed and movable pulleys
Depending on the combination they can have a lager mechanical advantage

19. Wheel and Axle
A wheel and axle is a simple machine consisting of two wheels of different sizes that rotate together

20. Wheel and Axle An effort force is usually applied to the larger wheel
The smaller wheel, also called the axle, exerts the resistant force
In many cases the , the larger wheel doesn’t look like a typical circular wheel

21. Wheel and Axle
The ideal mechanical advantage of the wheel and axle can be calculated by dividing the radius of the wheel (effort arm) by the radius of the axle (resistance arm)
IMA = radius of wheel
radius of axle

22. Gears Gears are modified wheel and axle machines
Effort is exerted on one gear, causing the other to turn
The larger gear is the effort gear, the smaller gear is the resistance gear

23. Inclined Plane
An inclined plane is a sloping surface used to raise objects
An inclined plane makes work easier because it increases the distance for the amount of work done
Increased distance means that less force is needed
work = force x distance

24. Inclined Plane
You can calculate ideal mechanical advantage of an inclined plane using distances
IMA = __effort distance__
resistance distance
IMA = length of slope
height of slope

25. The Screw The screw is an example of an inclined plane that moves
It is wrapped around a cylindrical post, the threads form a tiny ramp that runs from the tip to its top

26. The Wedge A wedge is an inclined plane with one or two sloping sides
Chisels, knives, and axe blades are examples
A wedge is a moving inclined plane, the material remains in one place while the wedge moves through it

27. Compound Machines
A compound machine is a combination of two or more simple machines
Even a tool as simple as an axe is a compound machine made up of a wedge and a lever

28. Mechanical Advantage of a Bicycle
The ratio of the resistance force exerted by the tires on the road to the effort force exerted by the rider on the pedals
Multi speed bikes can change gear ratios which change mechanical advantage
A MA of less than 1 sacrifices force to gain speed

29. Efficiency
Some energy you put into a machine is lost as thermal energy produced as a result of friction
The work put out by a machine is always less than the work put into it
Efficiency is a measure of how much of the work put into the machine is changed into useful work put out by the machine

30. Efficiency Efficiency = Wout X 100% Win Efficiency = Fr x dr X 100%
Fe x de
Many machines can be made more efficient by reducing friction
This is usually done by adding a lubricant such as oil or grease

31. Efficiency In the 1970’s cars were only about 15% efficient
Today cars are about 21% efficient
Most Coal power plants are only about 13% efficient

32. Power Power is the rate at which work is done
To calculate power, divide the work done by the time required to do the work
Power = work
time
P = W t

33. Power
Power is measured in watts, named for James Watt, who worked on the steam engine
A watt (W) is one joule per second

34. Power
One watt is about equal to the amount of power used to raise a glass of water from your knees to your mouth
Large amounts of power are expressed in kilowatts
One kilowatt (kW) = 1000 watts

35. HorsePower
Is the unit of power in the English system, for measuring the rate at which an engine or other prime mover can perform mechanical work. It is usually abbreviated hp. Its electrical equivalent is 746 watts, and the heat equivalent is 2545 British thermal units per hour. One horsepower was originally defined as the amount of power required to lift 33,000 pounds 1 foot in 1 minute, or 550 foot-pounds per second.
Scottish engineer and inventor James Watt established this value for the horsepower after determining in practical tests that horses could haul coal at the average rate of 22,000 foot-pounds per minute.