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## MACHINES and EFFICIENCY

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Title: MACHINES and EFFICIENCY

1
MACHINES and EFFICIENCY
• Chapter 9.8-9.9

2
Key Terms
• Work Force x distance
• Simple machine
• a device used to multiply forces or change the
direction of forces
• Compound machine
• A machine composed of two or more simple machines

3
Key Terms
• Input (effort)
• Input distance the distance you input the force
when using a machine
• Input force the force you use when using a
machine
• Output (resistance)
• Output distance the distance the object that
work is done on moves
• Output force the force required to move the
object without a machine (usually the weight of
the object in newtons)

4
Key Terms
• A unitless ratio that indicates the number of
times a machine multiplies your input force
• The calculated MA, does not consider friction
• The measured or real MA, does consider friction
• Because of friction, AMA lt IMA

5
A simple machine
• Multiplies and redirects force
• Does not reduce the amount of work to be done,
but makes work easier.
• MA gt 1 means that your input force will be less
• More leverage means more mechanical advantage
• If you increase MA, then
• Input force will decrease
• Input distance will increase

6
Key Terms
• Efficiency (a ratio)
• Is calculated using the following equations
• Useful work output/total work input

7
Key Terms
• Efficiency of a machine decreases as friction
increases
• Friction increases the thermal energy by
increasing molecular KE (non-mechanical energy)
• In other words friction causes the particles to
speed up, raising the average KE of the particles
(and temperature!)
• Friction causes the useful work output to be less
than the total work input

8
Key Terms
• When using a machine
• Work is done to move the object
• Work is done against friction
• Useful work output is the work done to move the
object
• Total work input is work done to move object
work done against friction

9
Simple Machines
• Two families

Lever
Inclined plane
--Lever --Pulley --Wheel and axle
--Ramp --Wedge --Screw
10
LEVER FAMILY
11
The Lever
fulcrum
12
Three Classes of Levers
• First class

Examples Crowbar See-saw
13
Three Classes of Lever
• Second class

Examples Wheelbarrow Door
14
Three Classes of Lever
• Third class

Examples Human arm Baseball bat
15
Calculating the Mechanical Advantage of a Lever
• MA input distance/output distance which is MA
length of effort arm/length of resistance arm.

Effort or input distance
0.5 m
Resistance or output distance
2.5 m
Effort arm
Resistance arm
16
Calculating the Mechanical Advantage of a Lever
• 2nd class lever
• 3rd class lever

2nd class levers decrease the input force but
increase the input distance.
3rd class levers reduce the output force, but
increase output distance and speed
17
• Which lever would have the highest mechanical

b has the largest input distance, giving the
largest MA
c
b
a
18
Pulley
Fixed pulley 1 support rope IMA 1
19
Pulleys
IMA 2
Two supporting ropes
20
Pulleys
IMA ?
2
21
Pulley
How many support ropes?
4
What is the IMA?
4
22
Wheel and Axle
• Wheel connected to a shaft

GIVES YOU LEVERAGE
23
INCLINED PLANE FAMILY
24
Inclined planes
• Ramps

25
Wedge
• Two inclined planes stuck together

26
Screw
• An inclined plane wrapped around a cylinder

27
What type of machine is this?
Compound made of two or more machines
Two 1st class levers