Work

Work definition corresponds to our everyday meaning of the word in that when you lift a brick 6 feet from the floor you do (1) as much work as when you lift it 3 feet.  Or suppose you lift 50 bricks to a height of 3 feet.  You do (2) times as much work as lifting one brick that high.

Work definition corresponds to our everyday meaning of the word in that when you lift a brick 6 feet from the floor you do twice as much work as when you lift it 3 feet. Or suppose you lift 50 bricks to a height of 3 feet. You do 50 times as much work as lifting one brick that high.

But here comes a conclusion that may seem odd.  After you lift a dozen bricks up to your waist, you are told by your boss to hold them there for 5 minutes.  Do you do work in holding them there?  To answer this, we must go back to our definition.  The force you exert is simply the weight of the 50 bricks.

1. In holding them waist-high, does the force move the bricks through a distance? (1)
2. Using the formula, calculate the total work done in holding the bricks. (2)

Formula: W = Fd

If force is measured in pounds and distance in feet, the unit of work is the ft.lb, or foot.pound.  In SI units, recall (from frame 5 of Chapter 2) that force is measured in newtons and distance in meters.  The unit of work is the newton.meter, called (1)