Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Name Date Work and Energy Before You Read Before you read the chapter, respond to these statements. 1. Write an A if you agree with the statement. 2. Write a D if you disagree with the statement. Before You Read Work and Machines • Holding a heavy object motionless involves a lot of work. • Energy is lost when an object is motionless. • A machine is a device that creates energy. • A light bulb transforms electrical energy into light and thermal energy. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Construct the Foldable as directed at the beginning of this chapter. Science Journal Diagram a bicycle and identify the parts you think are machines. Accept all reasonable answers. Work and Energy 43 Name Date Work and Energy Section 1 Work and Machines Skim Section 1 of your text. Write three questions that come to mind from reading the headings and the illustration captions. 1. Accept all reasonable responses. 2. 3. Review Vocabulary Define the word force. force a push or pull exerted on an object New Vocabulary Use your book or a dictionary to define these terms. machine simple machine compound machine efficiency application of a force through a distance a device that makes doing work easier does work with just one movement of the machine combination of two or more simple machines a measure of how much work put into a machine is turned into useful output by the machine mechanical advantage the ratio of the output force to the input force Academic Vocabulary Look up the words per and cent in a dictionory. percent 44 Work and Energy Then explain why 68 percent is the same as 68/100. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. work Name Date Section 1 Work and Machines What is work? I found this information on page . SE, p. 106 RE, p. 56 (continued) Create three sketches showing the following situations involving work. Accept all reasonable responses. A force is not doing A force is doing A force is not doing work, because the work. work, because there force does not point to is no motion. the direction of motion. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Sketch should show a force acting on some object that moves in the direction of the force. What is a machine? Sketch should show a force acting on an object that does not move. Complete the concept map relating simple and compound machines. I found this information on page . SE, p. 109 RE, p. 57 Sketch should show a force acting acting at right angles to the direction of motion. Machines Simple Machines Compound Machines does work with just one movement of the machine combination of two or more simple machines Sketch a nail and a screw. Explain which one uses less force and why. Answer: To drive a nail you have to exert a lot of energy on the hammer to force the nail into the wood. The screw uses less energy because the screw takes smaller movements to reach the same point (depth). Work and Energy 45 Name Date Section 1 Work and Machines Efficiency I found this information on page . SE, p. 110 RE, p. 58 (continued) Evaluate the efficiency of two identical-looking conveyor belts. Belt A can move a 10 newton weight one meter in 3 seconds. Belt B can move a 10 newton weight 2 meters in 3 seconds. (one joule ! 1 newton meter) The input work for both belts is 20 joules. Fill in the missing numbers below. What do you know? A Belt B Weight (newtons) 10 10 Distance (meters) 1 2 Time (seconds) 3 3 Joules = Newton/meter 10 Nm 6 Nm Joules 10 J 5J Input work (Win) 20 J 20 J Output work (Wout) 10 J 5J Efficiency (%) ! Wout " Win # 100 50 % 25 % CONNECT IT A child sits at the top of a slide at a playground. He wiggles forward slightly, and then slides all the way down with no further effort. Explain the source of the force acting on the child, and how you would calculate the work being done. Accept all reasonable responses. The force of gravity is acting on the child, causing him to slide. The work being done on the child is the vertical distance he slides times the force exerted, which is the height of the slide (in meters), times his weight (in newtons). 46 Work and Energy Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Belt