chap04 leyes de movimiento - 703_S1_096-103_GPS05 12:32 PM Page 96 The Laws of Motion sections 1 The First Two Laws of Motion 2 Gravity Lab Gravity and

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96sections1The First Two Laws of Motion2GravityLabGravity and Air Resistance3The Third Law of MotionLabThe Momentum of Colliding ObjectsVirtual LabHow is momentum conservedin a vehicle collision?Who’s a dummy?Crunch! This test dummy would have someexplaining to do if this were a traffic acci-dent. But in a test crash, the dummy playsan important role. The forces acting on itduring a crash are measured and analyzedin order to learn how to make cars safer.Explain which would be a safercar—a car with a front that crumples in a crash, or one witha front that doesn’t crumple.Science JournalThe Laws ofMotionTim Wright/CORBIS
97The Laws of MotionMake thefollowing Foldable to help youbetter understand Newton’slaws of motion as you read thechapter.Foldthe top of a vertical piece ofpaper down and the bottom up todivide the paper into thirds.Unfold and labelthe rows First Law,Second Law, Third Law.Find Main IdeasAs you read the chapter, listthe main ideas in the sections on the laws ofmotion under the appropriate column.STEP 2STEP 1The Force of GravityThe force of Earth’s gravity pulls all objectsdownward. However, objects such as rocksseem to fall faster than feathers or leaves. Doobjects with more mass fall faster?1.Measure the mass of a softball, a tennisball, and a flat sheet of paper. Copy thedata table below and record the masses.2.Drop the softball from a height of 2.5 mand use a stopwatch to measure the timeit takes for the softball to hit the floor.Record the time in your data table.3.Repeat step 2 using the tennis ball andthe flat sheet of paper. Record the timesin your data table.4.Crumple the flat sheet of paper into a ball,and measure the time for the crumpledpaper to fall 2.5 m. Record the time inyour data table.5.Think CriticallyWrite a paragraphcomparing the times it took each item tofall 2.5 m. From your data, infer if thespeed of a falling object depends on theobject’s mass.Start-Up ActivitiesPreview this chapter’s contentand activities at gpescience.comFalling Object DataObjectMassTimeSoftballTennis ballFlat paperCrumpled paperSecondLawThirdLawFirstLawTim Wright/CORBIS
98CHAPTER 4The Laws of MotionThe First Two Lawsof MotionReading GuideDefineNewton’s first law ofmotion.Explain how inertia and mass arerelated.DefineNewton’s second law ofmotion.Apply Newton’s second law ofmotion.Newton’s first two laws of motionexplain how forces cause the motionof objects to change.Review Vocabularynet force:the combination of allforces acting on an objectNew Vocabularyfirst law of motioninertiasecond law of motionNewton’s Laws of MotionWhen you lift a backpack, you exert a force on an object andcause it to move. The backpack initially was at rest. The forceyou exerted caused its velocity to change. But if you push down-ward on a table, the table doesn’t move. The force you applieddid not cause the velocity of the table to change. How are forcesand motion related?