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34 N 27 0 13 N 51 0 1/ 1 cm:5N 2/ 1 cm:2N

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1 cm:4 N 20 0 6.5 cm 26N 10 N 1 cm:10 N 4.2 cm 42N 42N 46 0 1 cm:8 N 1 cm:3 N F x = 40 N F y = 0 F x = 0 F y = -6 N

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Newtons 1st Law of Motion: If the ____________________ force, F net, acting on an object equals ________, then that object has ____________________. Its acceleration a = _____. It is said to be in __________________. zero constant velocity net (resultant) equilibrium 0 Because forces are ______________ and have ____________, the x and y _______________ of the forces often must be added up _______________ when there are forces along different _________. F net = 0 really means: ________ = 0 vectors directioncomponents separately net F x net F y axes

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Ex: A 20-N box on a table at rest 20-N F N = 20N w = 20 N Ex: A 20-N box at rest on a table being pushed down with a 5 N force. "At rest" __________ 20-N Free body diagrams: w = F N 5-N w = 20 N 5 N F N = 25 N "At rest" _______________ w + push = F N Both of these boxes are in ___________________. equilibrium

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Ex: Same box sliding to the right on a horizontal frictionless table at a constant velocity 2.0 m/s 20-N F N = 20N Draw only the __________, not the ____________ Notice: 1/ The free body diagram is the _________ as the first example. Both are in ___________________. 2/ No force is ___________ to keep box moving. The box will continue its motion ________________. equilibrium v = 2.0 m/s forces velocities needed forever w = 20N same "constant velocity" __________ w = F N

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Ex: The forces acting on a 20-N box are shown at right: F N = 20N w = 20 N pull = 10N F f = 10 N This box is in ___________________. It is either: 1/ _____________ (constant velocity = _____); 2/ or _____________ at a constant velocity. Unless other information is given, it is _______________ to tell if it is at rest or moving. at rest moving equilibrium 0 impossible

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3.0 N 4.0 N Ex. The three forces below are the only ones acting on an 2.0-kg object. What is the acceleration of the object? 5.0 N This object could be _______________ or moving with ____________________________. 0 at rest constant velocity The net force F net = _____ so a must = ____. 0 Add them up: 4.0 N 3.0 N 5.0 N

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Restatement of 1 st Law: If an object is ____________ or moving with _____________________, it is_________________. Then the net force (F net ) acting on it _________. lift = 1.3 MN w= 1.3 MN thrust = 300 kN F f (drag) = 300 kN weight 1.3 x 10 6 N thrust 75 x 10 3 N/engine x 4 engines at rest constant velocity in equilibrium = 0 Ex: A B-2 bomber flying at constant velocity:

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The air force

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Ex. The two forces shown below act on an object. What third force is needed to produce equilibrium? F1F1 First way to solve: Find resultant force F The answer is -F: F -F -F ___________________ the other two forces. F2F2 balances

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Second way to solve: 1. Add the two forces using head to tail method. 2. Add a force to "bring the total force to zero." original Notice: Both ways give ________________________ -F is NOT the ________________ of the other vectors. It is the force that ________________ the other vectors, making F net =________. It is sometimes called the ________________ because it is what is needed to produce ___________________. the same result resultant "balances out" equilibrant equilibrium -F F1F1 F2F2 F1F1 F2F2 head to tail: 0

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wire beam building weight Ex. Draw the vector that represents the force that the beam exerts on point A. A A T w beam force The beam force is the ________________. It must be added to the other forces so that ___________ equilibrant F net = 0

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Ex. Increasing angle between 2 wires supporting a picture: Case 1: vertical wires Case 2: greater angle Case 3: even greater angle 10 N w = 10 N T = ____ in each wire w = 10 N 10 N 12 1 1 2 2 1 2 1 2 T = ____ in each wire T = ____ in each wire As increases, the tension _______________. 5 1 2 7 10 increases

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A net force is ________________ to maintain motion. An object will maintain its motion in the ________________ of a net force. This idea was discovered by _____________. An object in motion tends to ____________________, and an object at rest tends to _________________. The _______________________ that makes this true is called its ___________. more __________ more___________ inertia mass Ex. What has more inertia, a truck or a baseball? property of matter inertia absence not needed Galileo stay in motion stay at rest mass inertia truck

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Inertia is the tendency of an object to _________________________. More inertia (mass) means it is __________________ for an object to… 1/ …_____________________ when it is at rest; 2/ … __________ when it is already moving; and, 3/ … ____________________ from a straight path. In other words, ______________ is why an object needs __________________ to maintain its motion. This is why Newton's _____________ is called the ________________. resist changes in motion more difficult start moving stop move sideways Law of Inertia 1 st Law no net force inertia F net a equilibrium = 0 Law of Inertia

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Open your 3-ring binder to the Worksheet Table of Contents. Record the title of the worksheet: Newtons First Law WS

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