CHAPTER 14 Study Guide

14.1 Work and Power

Key Concepts

• $\mathrm{Work} = \mathrm{Force} \times \mathrm{Distance}$. Work is done on an object when a force acts in the same direction as the object moves.

• $\mathrm{Power} = \mathrm{Work} ÷ \mathrm{Time}$. Power is the rate of doing work. Doing work faster requires more power.

Vocabulary

• work, p. 412

• joule, p. 414

• power, p. 414

• watt, p. 415

• horsepower, p. 416

14.2 Work and Machines

Key Concepts

• Machines make work easier by changing the force needed, the direction of the force, or the distance over which the force acts.

• Work output (done by a machine) is always less than the work input (done on the machine).

Vocabulary

• machine, p. 417

• input force, p. 419

• input distance, p. 419

• work output, p. 419

• output force, p. 420

• output distance, p. 420

• work output, p. 420

14.3 Mechanical Advantage and Efficiency

Key Concepts

• Friction is present in all machines. Because of friction, the actual mechanical advantage is always less than the ideal mechanical advantage.

• $Actualmechanicaladvantage=\genfrac{}{}{0.1ex}{}{Outputforce}{Inputforce}$

• $Idealmechanicaladvantage=\genfrac{}{}{0.1ex}{}{Inputdistance}{Outputdistance}$

• $Efficiency=\genfrac{}{}{0.1ex}{}{Workoutput}{Workinput}\times 100\%$

• Because of friction, the efficiency of any machine is always less than 100 percent.

Vocabulary

• mechanical advantage, p. 421

• actual mechanical advantage, p. 422

• ideal mechanical advantage, p. 423

• efficiency, p. 425

14.4 Simple Machines

Key Concepts

• The six types of simple machines are the lever, the wheel and axle, the inclined plane, the wedge, the screw, and the pulley.

Vocabulary

• lever, p. 428

• fulcrum, p. 428

• input arm, p. 428

• output arm, p. 428

• wheel and axle, p. 430

• inclined plane, p. 431

• wedge, p. 431

• screw, p. 431

• pulley, p. 432

• compound machine, p. 435

Thinking Visually

Concept Map Use information from the chapter to complete the concept map below.

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