2 W = F • d Unit= Joule

5 For there to be work on an object, there must be a displacement and the force must cause that displacement

Is work done here? pushing on a wall pushing a boat out to sea 6 Is work done here? pushing on a wall pushing a boat out to sea lifting up a box holding up a box

Which car does the most work? 7 Which car does the most work?

W = F • d = (400 N) • (0.25 m) Calculating Work 8 When doing a chin-up, a physics student lifts her 40-kg body a distance of 0.25 meters in 2 seconds. How much work is done by the student's biceps? W = F • d = (400 N) • (0.25 m) W = 100 J

9 Work has nothing to do with the amount of time that this force acts to cause the displacement. Sometimes, the work is done very quickly and other times the work is done rather slowly.

POWER The rate of energy transfer. How fast work is done. 10 The rate of energy transfer. How fast work is done. Machines with different power ratings do the same amount of work...just in different amounts times.

12

14 watt (W) 1W = 1 J/s One watt is equal to a power rate of one joule of work per second of time. 1Kilowatt = 1000 Watts

15 Calculating Power

16 W = F • d = (400 N) • (0.25 m) W = 100 N-m W = 100 J When doing a chin-up, a physics student lifts her 40-kg body a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps? The work done to lift her body is W = F • d = (400 N) • (0.25 m) W = 100 N-m W = 100 J The power is the work/time ratio which is (100 J) / (2 seconds) = 50 Watts.