# ch4 continued - TA recitation HSS 2.01.36 Friday 3 4pm 2 01...

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TA recitation: HSS 2 01 36 Friday 3 4pm TA recitation: HSS 2.01.36 Friday 3-4pm Chapter 4 The Laws of Motion continued 1

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Conceptual Question 2 If gold were sold by weight, would you rather buy it in Denver or in Death Valley? If it were sold by mass in which of If it were sold by mass, in which of the two locations would you prefer to buy it? 2
Gravitational Force Newton’s Law of Universal Gravitation : 2 1 m m G F Every particle in the Universe attracts every other particle with a force that is directly proportional to the product of 2 g r their masses and inversely proportional to the square of the distance between them G 6 67 X 10 -11 N m 2 /kg 2 G=6.67 X 10 3

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Exercise 4.3 To one significant digit, find the force exerted by the Moon on a 70-kg man on Earth. The Moon has a mass of 7 36 X 10 22 kg and is 3 84 X 10 8 m a mass of 7.36 X 10 kg and is 3.84 X 10 from Earth. If the distance between the Earth and the Moon was suddenly reduced by ½, how would that force change? 4
Newton’s Third Law Hammer exerts a force on the nail, accelerating it into the wall. Nail exerts a force on the hammer, slowing it down and stopping it. 5

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Newton’s Third Law If object 1 and object 2 interact, the force exerted by object 1 on object 2 is equal in magnitude but opposite in direction to the force exerted by object 2 on object 1. 12 21   F F Equivalent to saying a single isolated force cannot exist 6
Action and Reaction Forces F 12 may be called the action force and F 21 th ti f the reaction force Actually, either force can be the action or the reaction force The action and reaction forces act on different objects 7

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Some Action-Reaction Pairs 8
Forces Acting on an Object Newton’s Law use the forces acting on bj t an object are acting on the TV g and n F are acting on other ' ' g and n F objects 9

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Quick Quiz 4.3 A small sports car collides head-on with a massive truck. The greater impact force ( in magnitude) acts on (a) the car (b) the truck (c) neither, the force is the same on both. Which vehicle undergoes the greater magnitude acceleration? (a) the car (b) the truck (c) the accelerations are the same. 10