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

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

Ex: Same box sliding to the right on a horizontal frictionless table at a constant velocity 2.0 m/s v = 2.0 m/s FN = 20N 20-N w = 20N "constant velocity"  __________ w = FN velocities Draw only the __________ , not the ____________ forces 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 ________________. same equilibrium needed forever

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

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

If an object is ____________ or moving with Restatement of 1st Law: If an object is ____________ or moving with _____________________, it is_________________. Then the net force (Fnet ) acting on it _________ . at rest constant velocity in equilibrium = 0 Ex: A B-2 bomber flying at constant velocity: lift = 1.3 MN Ff (drag) = 300 kN thrust = 300 kN weight ≈ 1.3 x 106 N thrust ≈ 75 x 103 N/engine x 4 engines w= 1.3 MN

Ex. The two forces shown below act on an object. What third force is needed to produce equilibrium? F1 F2 First way to solve: Find resultant force F The answer is -F: F -F balances -F ___________________ the other two forces.

Add the two forces using head to tail method. Second way to solve: Add the two forces using head to tail method. Add a force to "bring the total force to zero." original head to tail: F1 F2 F1 -F F2 Notice: Both ways give ________________________ -F is NOT the ________________ of the other vectors. It is the force that ________________ the other vectors, making Fnet =________. It is sometimes called the ________________ because it is what is needed to produce ___________________ . the same result resultant "balances out" equilibrant equilibrium

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

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

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 ___________ . not needed absence Galileo stay in motion stay at rest property of matter inertia Ex. What has more inertia, a truck or a baseball? truck inertia more __________ more___________ mass inertia mass

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 inertia no net force equilibrium Law of Inertia 1st Law Law of Inertia Fnet a = 0 = 0