Chapter 2.1.2 Work in Mechanical Systems Principles of Technology I Edinburg North High School.
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Chapter 2.1.2 Chapter 2.1.2 Work in Mechanical Work in Mechanical Systems Systems Principles of Technology Principles of Technology I I Edinburg North High Edinburg North High School School
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Transcript of Chapter 2.1.2 Work in Mechanical Systems Principles of Technology I Edinburg North High School.
Chapter 2.1.2Chapter 2.1.2Work in Mechanical SystemsWork in Mechanical Systems
Principles of Technology IPrinciples of Technology I
Edinburg North High SchoolEdinburg North High School
Notes 2.1.1Work in Mechanical Systems
Objectives:• Identify basic machines.• For a given machine, identify the input and output
work.• Explain how efficiency relates to input and output
work for a mechanical system.• Calculate efficiency for non-ideal (real machines)
Machines
• Machines can make work easier by:• changing the direction of the force used to do the work;• and multiplying the force used to do the work.
• In an ideal machine, the work put into the machine is equal to the work coming out of the machine.
outin WW
An Inclined Plane (or Ramp)
Mechanical Advantage
• Mechanical Advantage (MA) is the number of times the output force is multiplied by a machine.
• If in an ideal machine
• then
• By definition of MA
outin WW
outoutinin dFdF
out
in
in
out
d
d
F
FMA
Six Types of Machine in Two Families
Real Machines Are Not 100% Efficient
• Machines are designed to convert input work into useful forms of energy or output work.
• In real machines the output work is always less than the input work.• Some input work has to overcome undesired loses such as
the negative work of friction.
• Machines are often rated by efficiency or percent efficiency.• Efficiency in real machines is always less than 1, or 100%
in
out
W
WEfficiency
%100in
out
W
WEfficiency Percent
Sample Problem
• A sailor uses a rope and an old, squeaky pulley to raise a sail that weighs 140 N. He finds that he must do 180 J of work on the rope in order to raise the sail by 1 m (doing 140 J of work on the sail). What is the efficiency of the pulley? Express your answer as a percentage.
Example 2.3 Work and Efficiency for a Block and Tackle, p. 89
• The block and tackle shown in figure 2.3 (p. 88) is used to lift an automobile engine. The engine weighs 600 lb and is raised 0.9 ft. The operator pulls with a force of 100 lb over a distance of 6 ft. Calculate the efficiency of the block and tackle system.
