# Newton’s 2 nd, 3 rd laws, LUG Thursday, October 2, 2014.

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Newton’s 2 nd, 3 rd laws, LUG Thursday, October 2, 2014

Thursday, 10/2 Unit 3: Work and Forces  If you are new to the class please come see me.  Pick up warm-up from Physics bin  Read the ‘I can’ statements on the side board.  Review dates below  Upcoming dates  Wednesday, 10/8 – quiz  Friday, 10/9 – Unit 3 test  Friday, 10/24 – last day to turn in 2SW extra credit  Friday, 10/31 – end of 2SW

Warm-up A rock of mass 5.0 kg is at rest on the ground. For each situation described, draw a free body diagram (forces must be to scale) and calculate the forces acting on the rock, and describe the motion (direction moving and if it is accelerating). A) The rock is at rest on the ground. Calculate the normal force exerted by the ground on the rock. b) A rope is tied to the rock and is used to pull the rock upwards. The rock accelerates at 5.0 m/s 2. Calculate the force of tension in the rope. c) As the rock is pulled upwards, the force exerted by the rope is reduced to 40 N. Calculate the acceleration of the rock.

Review in class problems

Balloon Demo

Summarize Newton’s 3 rd Law of Motion

Newton’s 3 rd Law, the Law of Interaction If (object 1) exerts a (type) force in the (direction) direction on (object 2), then (object 2) is exerting a (same type) force directed (opposite direction) on (object 1) simultaneously.

Source: http://www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law

http://www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law

Quiz  Put your phone in your bag. If you don’t have a bag put your phone on my desk  When you are done flip your quiz over.

Review Quiz

Law of Universal Gravitation

Video  http://dsc.discovery.com/videos/assignment- discovery-shorts-newtons-explanation-of- gravity.html http://dsc.discovery.com/videos/assignment- discovery-shorts-newtons-explanation-of- gravity.html

Take LUG notes

Review Equation  What does the G in the equation mean? Will it ever change?  Describe the relationship between mass and distance between the objects.  What variable has greatest role in evaluating the force of gravity between objects? Support your answer

Practice Problem 1 Tom has a mass of 70.0-kg and Sally has a mass of 50.0-kg. Tom and Sally are standing 20.0m apart on the dance floor. Sally looks up and sees Tom. She feels an attraction. If the attraction is gravitational, find its size. Assume that both Tom and Sally can be replaced by spherical masses.

Practice Problem 2  What is the gravitational attraction between two spheres ( m sphere = 1.67 X 10 -27 kg) at a distance of 5.0 X 10 -15 m? 7.44 x10 -36 N

Practice

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