1. 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 of Current Generation and Use U NIT 3 – E NERGY AND P OWER Topics Covered

2. IOT POLY ENGINEERING 3-13 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.

3. IOT POLY ENGINEERING 3-13 WORK 1.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

4. IOT POLY ENGINEERING 3-13 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.

5. IOT POLY ENGINEERING 3-13 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?

6. IOT POLY ENGINEERING 3-13 WORK WORK = 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 lbsW = F x d d = 1,450 ft. = (1.3 lb) x (1,450 ft.) W = ?W = 1,885 ft-lb

7. IOT POLY ENGINEERING 3-13 Work You are pulling a wagon with a 20 lbs of force at a 60 o angle. You pull the wagon 10 feet, how much work did you do? 20 lbs 60 o Fy Fx

8. IOT POLY ENGINEERING 3-13 WORK Units for Force English SystemMetric lbsNewton (N)=kg-m/s 2 Units for Work English SystemMetric ft-lbsJoule (J) = N*m

9. IOT POLY ENGINEERING 3-13 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? Efficiency is always less than or equal to 100%

10. IOT POLY ENGINEERING 3-13 Efficiency Units for Efficiency No Units or percentage

11. IOT POLY ENGINEERING 3-13 Efficiency You are pulling a wagon with a 20 lbs of force at a 60 o angle. How efficiently are you using your pulling 20 lbs 60 o Fy Fx

12. IOT POLY ENGINEERING 3-13 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

13. IOT POLY ENGINEERING 3-13 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?

14. IOT POLY ENGINEERING 3-13 Work You are pulling a wagon with a 20 lbs of force at a 60 o angle. You pull the wagon 10 feet in 10 seconds, how much power did you use? 20 lbs 60 o Fy Fx

15. IOT POLY ENGINEERING 3-13 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