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Thursday Honors PS

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Homework Pg 369 Problems 22-27

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Leading Ideas Newton’s 1 st law Newton’s second law Weight = mass x 10 (9.8) Difference between mass and weight

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To find the weight of an object Weight = mass x acceleration of gravity On Earth: acceleration due to gravity is equal to about 10 (9.8)

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Mass and Weight Mass: –Amount of stuff –Unchanging –Measure of Inertia –kg Weight: –Force of gravity –Changes because of location –N

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Answers to homework 22) 10 m/s 2 23) 23 N 24) 2.1 kg 25).04 m/s 2 26) 15 N 27) 43.75 N 28) 3.7 N 29) 58.5 N

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Additional Problems A 2.5 kg hula hoop is pushed forward with a force of 45.9 N. What is it’s acceleration?

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Answer F = ma F = 45.9 Nm = 2.5 kg A = 45.9 / 2.5 = 18.4 m/s 2

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Make up a problem Object : _______________ Amount of net force: __________ Mass of object: ____________ Solve for acceleration

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Example problem A 1540 kg car starts from rest and accelerates to 50.7 m/s in 13.8 seconds. What is the net force on the car that causes this acceleration?

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Answer 1540 kg = mass Rest = 0 m/s = initial velocity 50.7 m/s = final velocity 13.8 sec = time Want net force, but need to find acceleration a = (v f - v i ) / t then F net = ma a= 3.7 m/s 2 F net = 5700 N

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New homework Handout #3 Working with Newton’s 2 nd Law Review conversions, acceleration All questions are in book Pg 852 3,4 Pg 857 89-95 To be handed in on Monday

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Newton’s third Law

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3 rd Law For every _____________ There is an __________ but opposite __________.

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For every action there is an equal and opposite reaction Forces come in pairs –Equal in size –Opposite in direction –Applied to different objects

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Examples of 3 rd law

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Actions that can be related to 3 rd law in the classroom

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If all forces are equal and opposite, how does anything move?

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Answer Though equal in size, the forces act on different objects Force of ground on box Force of box on ground

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Trebuchet

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To change the motion of something Need to have a net force (unbalanced forces) on the object in order to change its motion Force of rope on box Friction force

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Free Body Diagrams Represent the object by a simple geometric shape or a dot Represent all forces on that object by arrows that originate from shape/dot Only represent the forces that are applied to the object, NOT forces the object applies to other things

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What would be the free body diagram of ….. What are the forces on the dog?

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Answer Dog Applied force of ground pushing paws forward Reactive force of ground Force of leash Weight of dog

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Create a free-body diagram of one of the dancers

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Create a free-body diagram of the ball

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Draw a free-body diagram of the rock climber

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