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Transcript
Name Date Forces and Newton’s Laws Section 3 Using Newton’s Laws Skim through Section 3 of your book. 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 momentum using a dictionary or your book. momentum property of a moving object that equals its mass times its velocity New Vocabulary State the definitions of the terms below as found in your book. air resistance a friction-like force opposing the motion of objects that move centripetal force law of conservation of momentum a force exerted towards the center of a curved path states that if a group of objects exerts forces only on each other, their total momentum does not change Academic Use a dictionary to define initial. Then use it as an adjective in a Vocabulary sentence to show its scientific meaning. initial the first; Student responses will vary. 38 Forces and Newton’s Laws Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. through the air Name Date Section 3 Using Newton’s Laws What happens in a crash? I found this information on page . Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. SE, p. 86 RE, p. 50 Newton’s Second Law and Gravitational Acceleration I found this information on page . SE, p. 87 RE, p. 51 (continued) Analyze the effects on a passenger riding in a car traveling at 50 km/h that collides head-on with a solid object. Without Restraints With Safety Belts and Air Bags Passenger continues moving forward. Passenger is slowed by the safety belt. Passenger slams into dashboard, steering wheel, or front seats. Passenger is cushioned by the air bag. Passenger may be thrown from the car. Passenger stays in the car. Analyze the formula W mg to explain how an object’s weight can change even when its mass remains constant. Accept all reasonable responses. Even though m remains constant, g can change because it represents the strength of local gravity. If g changes, then W changes. On Earth, g is about 9.8 m/s2, but on the Moon it is 1/6 that. On a larger planet it is greater. In space, far away from any planet or other large body, g is essentially zero and an object has no weight at all, but its mass will not change. Air Resistance I found this information on page . SE, pp. 87–88 RE, pp. 51–52 Contrast the terminal velocity of a parachutist with an open chute to the terminal velocity of the same parachutist with a closed chute. Accept all reasonable responses. The parachutist will have a lower terminal velocity with the chute open than with it closed. Because an open chute catches much more air than a closed one, the air resistance needed to counteract the parachutist’s weight is achieved at a much lower velocity with an open chute than with a closed one. Forces and Newton’s Laws 39 Name Date Section 3 Using Newton’s Laws Weightlessness and Free Fall (continued) Distinguish between an object that is truly weightless and an object that is weightless because it is in free fall. I found this information on page . Accept all reasonable responses. True weightlessness requires the SE, p. 89 RE, p. 52 total absence of gravity. Weightlessness in free fall is really just the appearance of weightlessness due to the fact that, if the object were placed on a scale during the free fall, the scale would read zero. I found this information on page . SE, p. 90 RE, p. 53 Force and Momentum I found this information on page . SE, p. 91 RE, p. 54 Create a top view of an object moving in a circle at constant speed, such as a ball on a string. Show at least two positions of the object. At each position, draw an arrow for the object’s velocity and another arrow for the centripetal acceleration of the object. Velocity Centripetal acceleration Velocity Calculate the force that is needed to propel a rocket into space if the rocket weighs 10,000 kg and the escape velocity for Earth’s gravity is 11 km/s. (Hint: use the formula F ma). Fill in the information below before calculating. Mass 10,000 kg Initial velocity 0 km/s Final velocity 11 km/s Time 10 minutes Force 66,000,000 N S UMMARIZE I T laws of motion. 40 Forces and Newton’s Laws After Reading this chapter, summarize Newton's three Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Centripetal Forces Name Date Tie It Together Forces and Newton’s Laws Combine some of what you have learned about forces in this chapter into a picture of a wooden block sliding across a table. Use arrows to show the following: • As the block slides, friction with the table slows the block down. • Gravity pulls the block downward. • The force of gravity is balanced by an upward force exerted by the table on the block. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Drawing should show friction as a horizontal arrow, gravity as a downward arrow, and the force of the table on the block as an upward arrow. If the student also draws an arrow showing the block’s motion, this should point in the opposite direction from the friction force. Suppose the block has a mass of 0.2 kg. Use W mg, with g 9.8 m/s 2, to calculate the weight of the block. W mg (0.20 kg)(9.8 m/s2) 1.96 N The block continues to slide until it strikes a second block. Draw this event below. Use arrows to show the following: • During the collision, the first block exerts a force on second block which causes the second block to move. • The second block exerts an equal and opposite reaction force on the first block, slowing it down. The two forces should appear as horizontal arrows of equal length, pointing in opposite directions. Forces and Newton’s Laws 41 Name Date Forces and Newton’s Laws Chapter Wrap-Up In the left column, copy the questions you listed in the Chapter Preview. In the right column, write down the answers you discovered as you worked through the chapter. W What I wanted to find out Accept all reasonable responses. L What I learned Check to make sure answers to questions on left are correct. Review Review the information you included in your Foldable. Study your Science Notebook on this chapter. Study the definitions of vocabulary words. Review daily homework assignments. Re-read the chapter and review the charts, graphs, and illustrations. Review the Self Check at the end of each section. Look over the Chapter Review at the end of the chapter. S UMMARIZE I T learned about forces. 42 Forces and Newton’s Laws After reading this chapter, list three things you have Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Use this checklist to help you study.