IOT POLY ENGINEERING 3-9 1.Energy Sources – Fuels and Power Plants 2.Trigonometry and Vectors 3.Classical Mechanics: Force, Work, Energy, and Power 4.Impacts.

IOT

POLY ENGINEERING3-9

1. Energy Sources – Fuels and Power Plants

2. Trigonometry and Vectors3. Classical Mechanics:

Force, Work, Energy, and Power4. Impacts of Current Generation

and Use

UNIT 3 – ENERGY AND POWER

Topics Covered

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POLY ENGINEERING3-13

WORK

• The man below is holding 1 ton above his head. Is he doing work?No, the object is not moving.

• Describe the work he did do:Lifting the 1 ton from the ground to above his head.

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POLY ENGINEERING3-13

WORK1. Velocity, acceleration, force, etc. mean nearly the same

thing in everyday life as they do in physics.2. Work means something distinctly different.3. Consider the following:

1) Hold a book at arm’s length for three minutes.2) Your arm gets tired.3) Did you do work?4) No, you did no work whatsoever.

4. You exerted a force to support the book, but you did not move it.

5. A force does no work if the object doesn’t move

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POLY ENGINEERING3-13

WORK

WORK = FORCE x DISTANCE

The work W done on an object by an agent exerting a constant force on the object is the product of the component of the force in the direction of the displacement and the magnitude of the

displacement.

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POLY ENGINEERING3-13

WORK

WORK = FORCE x DISTANCE

W = F x d

Consider the 1.3-lb ball below, sitting at rest. How much work is gravity doing on the ball?

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POLY ENGINEERING3-13

WORKWORK = FORCE x DISTANCE

W = F x d

Now consider the 1.3-lb ball below, falling 1,450 ft from the top of Sears Tower. How much work will have gravity done on the ball

by the time it hits the ground?

F = 1.3 lbs W = F x dd = 1,450 ft. = (1.3 lb) x (1,450 ft.)W = ? W = 1,885 ft-lb

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POLY ENGINEERING3-13

Work

You are pulling a wagon with a 20 lbs of force at a 60o angle. You pull the wagon 10 feet, how much work did you do?

20 lbs

60oFy

Fx

lbsFFx 102

12060cos

lbsftftlbsdFWork x 1001010

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POLY ENGINEERING3-13

WORK

Units for ForceEnglish System Metriclbs Newton

(N)=kg-m/s2

Units for WorkEnglish System Metricft-lbs Joule (J) = N*m

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POLY ENGINEERING3-13

Efficiency

Efficiency compares how well you did to the best that you could have done.A basketball player shoots 20 free throws and makes 15. What is his shooting percentage/efficiency?

%75%100*20

15

havecouldyoubest

didyouhowEfficiency

Efficiency is always less than or equal to 100%

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POLY ENGINEERING3-13

Efficiency

Units for EfficiencyNo Units or percentage

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POLY ENGINEERING3-13

Efficiency

You are pulling a wagon with a 20 lbs of force at a 60o angle. How efficiently are you using your pulling

20 lbs

60oFy

Fx

lbsFFx 102

12060cos

%505.020

10or

lbs

lbsEfficiency

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POLY ENGINEERING3-13

POWER

Power is the rate of doing Work

P =

The less time it takes….The more power

Units:Watts, Horsepower, Ft-

lbs/s

W t

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POLY ENGINEERING3-13

POWER

1. Three Buddhist monks walk up stairs to a temple.2. Each weighs 150 lbs and climbs height of 100’.3. One climbs faster than the other two.4. Who does more work?5. They all do the same work:

W = F x d (force for all three is 150 lb) = (150 lb)(100’)W = 15,000 ft-lb

6. Who has greater power?

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POLY ENGINEERING3-13

Work

You are pulling a wagon with a 20 lbs of force at a 60o angle. You pull the wagon 10 feet in 10 seconds, how much power did you use?

20 lbs

60oFy

Fx lbsFFx 102

12060cos

s

lbsft

s

lbsft

time

WorkPower

10

10

100

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POLY ENGINEERING3-13

Tomorrow

WORKSHEET

Problem Solving Steps:

1. Write given, sketch and label a diagram

2. Write equation/formula

3. Substitute values and solve

4. Check answer

5. Box answer