Upload
homer-wade
View
213
Download
0
Tags:
Embed Size (px)
Citation preview
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
IOT
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.
IOT
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
IOT
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.
IOT
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?
IOT
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
IOT
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
IOT
POLY ENGINEERING3-13
WORK
Units for ForceEnglish System Metriclbs Newton
(N)=kg-m/s2
Units for WorkEnglish System Metricft-lbs Joule (J) = N*m
IOT
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%
IOT
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
IOT
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
IOT
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?
IOT
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