a) What force does Trask exert on Butch? F - ^\ ~\™ *

FORCES AND ACCELERATIONForce: A push or a pull , .When an unbalanced <strong>force</strong> is <strong>exert</strong>ed on an object, the object accelerates in the direction of the <strong>force</strong>. The acceleration isproportional lo the <strong>force</strong> and inversely proportional to the mass of the object.Newton's second law <strong>force</strong> = (mass) (acceleration) or F = maThe unbalanced <strong>force</strong> is called the net <strong>force</strong>, or resultant of all the <strong>force</strong>s acting on the system. The SI unit tor torce is thenewton which equals one kilogram meter per second squared (N = kg-m/s2) You can think of a newlon as being aboutequivalent to the weight of a stick of butter. Mass, or the amount of matter in an object, <strong>does</strong> not change regardless ofwhere an object is located. It is a constanl property of any object. However, do not confuse mass with weight! The weighlof an object is simply the gravitational <strong>force</strong> acting on the object. Therefore, if an object is moved away from Earth to alocation where g is no longer 9.8 m/s2, the object will no longer have the same weight as it did on Earth. The equation forweight is just a specific case of F = ma. weight = (mass)(acceleration due to gravity) or w = mg Because of itsweight an object pushes against a surface on which it lies. By Newton's third law, the surface pushes back on the object.This push, which is called the normal <strong>force</strong>, is always perpendicular to the surface on which the object restsExample 1: Felicia, the ballet dancer, has a mass of 45.0 kg. a) <strong>What</strong> is Felicia's weight on Earth? Vb) WhaL is Felicia's mass on Jupiter, where the acceleration due to gravity is 25.0 m/s ? 45.0 kgc) <strong>What</strong> is Felicia's weight on Jupiter? \si - mg - t^W V f ^ 7 =Example 2: Butch, the 72.0-kg star quarterback of Belmont High School's football team, collides with <strong>Trask</strong>, a stationaryleft tackle, and is brought to a stop with an acceleration of -20.0 m/s2 v _ mqo Ma) <strong>What</strong> <strong>force</strong> <strong>does</strong> <strong>Trask</strong> <strong>exert</strong> on Butch? F - ^\ ~\ *b) <strong>What</strong> <strong>force</strong> <strong>does</strong> Butch <strong>exert</strong> on <strong>Trask</strong>?+ i1"'Example 3: A 20-g sparrow Hying toward a bird feeder mistakes the pane of glass in a window for an opening and slamsinto it with a <strong>force</strong> of 2.0 N. <strong>What</strong> is the bird's acceleration? F *

Name Period DateNewton's Third LawConcept-DevelopmentPractice Page6-11. In the example below, the action-reaction pair is shown by the arrows (vectors), and the actionreactiondescribed in words. In {a) through (g) draw the other arrow (vector) and state the reactionto the given action. Then make up your own example in (h).Example:c.l'Fist hits wall.Wall hits fist.Head bumps ball.Ball bumps head.Windshield hits bug.Bug hits windshield.Bat hitsball.Hand touchesnose.Hand pulls on flower.Ball hits bat.Nose touches hand.(e) Flower pulls on hand.Student drawing (open)Athlete pushes barupward.Compressed air pushesballoon surface outward./j^ Thing A acts onThing B.Bar pushes athletedownward.(g).Balloon surface pushescompressed air inward.Thing B reacts onThing A.2. Draw arrows to show the chain of at least six pairs of action-reaction <strong>force</strong>s below.VYOU CAN'T TOUCHWITHOUT BEING TOUCHEDNEWTON'S THIRD LAWconceptual©Addison-Wesley Publishing Company, Inc. All rights reserved. Chapter 6 Newton's Third Law of Motion—Action and Reaction 27