Forces - 1 - Net Force & Equilibrium

Unit 2: Forces (Quantum ch12,13,17) Types, Net Forces, Equilibrium and Equilibrant 1 2.0 Force: Is an agent that can act on an object to change its motion or distort it. Makes things happen  Ex. slow down, stretch, compress  Ex. push & pull Agent that objects use to interact with one another Unit: newton (N) Types of Forces: Gravity Friction Normal Centripetal Tension Etc… Net force: the resultant of many forces acting on the same object a.k.a. an “unbalanced” force Fnet solve with vector addition Free Body Diagrams: Diagrams that show, with vector arrows, all the forces exerted on a body/object Object represented by a point that corresponds to the object’s center FN FT2 Flift FT1 Fdrive force Fg Fg Fg Ff Ex. Forces of 10.0N [E] and 20.0N [W] are acting on a block of wood. What is the net force acting on the block? 20.0N [W] 10.0N [E] Fnet = 10.0 N [W] Ex. Vector Addition Two children are pulling at the same toy. One child pulls with a force of 3.00 N [30.0° N of E] and the other at a force of 2.00 N [50.0° S of W]. What is the net force acting on the toy? 3.00N [30°N of E] F2x = 2.5981 N [E] 2.00N [50°S of W] F1x = 1.2856 N [W] F1y = 1.5321 N [S] F2y = 1.5000 N [N] Ex. Vector Addition Fx = 1.3125 N [E] Fy = 0.0321 N [S] Pythagoras & Trig Fnet=1.31 N [1.4°S of E] 3.00N [30°N of E] F2x = 2.5981 N [E] 2.00N [50°S of W] F1x = 1.2856 N [W] F1y = 1.5321 N [S] F2y = 1.5000 N [N] Ex. Two boys are trying to move a rock. One boy applies a force of 400.0N [30.0°E of N] and the other applies a force of 500.0N [20.0°N of W]. Determine the net force. 400N [30°E of N] 500N [20°N of W] F2x = 469.846N [W] F2y = 171.010N [N] F1x = 200.0N [E] F1y = 346.410N [N] Ex. Fx = 269.846 N [W] Pythagoras Fy = 517.420 N [N] & Trig 583.558 N [27.5430°W of N] Fnet=583.6 N [27.5°W of N 400N [30°E of N] 500N [20°N of W] F2x = 469.846N [W] F2y = 171.010N [N] F1x = 200.0N [E] F1y = 346.410N [N] 2.1 Equilibrium: ◼ An object in a state of equilibrium has a net force of zero ◼ Static Equilibrium:  when ◼ a body is at rest Dynamic Equilibrium:  When a body is moving with uniform velocity (i.e. not speeding up, slowing down, changing direction etc.) 2.2 Equilibrant:  Force added to put an object in equilibrium  Equal in magnitude, but opposite in direction to the resultant of the other forces  Written as Feq Ex. A block is being pulled by two different people. What force must a third person exert in order to put this system into equilibrium? F1 = 12.0N [N] F2 = 16.0N [E] F3 = ? equilibrant = magnitude of the resultant of other vectors 16.0N Fnet = 20.0 N [53.1oE of N] 12.0N  Feq = 20.0 N [53.1oW of S] Ex. A log is being pulled out of the bush by two four-wheelers attached to the log with two separate ropes. The forces acting on the log are 200.0N [35.0oW of S] and 400.0N [20.0oE of S]. Determine the equilibrant for the concurrent forces. 35o 20o 200N 400N 35o 20o 200N 400N ? sin 20 = 400 o ? sin 35 = 200 o 114.715N [W] 136.808N [E] ? cos 20 = 400 o ? cos 35 = 200 o 163.830N [S] 375.877N [S] 114.715N [W] 136.808N [E] 22.093N [E] Σx = -114.715N + 136.808N = 22.093N 163.830N [S] 375.877N [S] 539.707N [S] Σy = -163.830N – 375.877N = -539.707N 22.0930N  Fnet = 540.2 N [87.7oS of E] 539.707N Feq = 540.2 N [87.7oN of W] Ex. A hot air balloon whose weight is 1000.0N is ready to lift off. It is tethered by 2 ropes at 30.0o to the vertical. The hot air’s lifting force is 4000.0N. FLifting = 4000N weight = 1000N 30o What is the magnitude of the tension, in N, in each rope? Ex. vectors, gives a Adding So, the vertical 3000N lifting force. tension on the ropes Ropes act as equilibrant. is 3000N total OR 1500N each FLifting = 4000N FT = 1.73x103 N weight = 1000N 1500N 30o What is the magnitude of the tension, in N, in each rope? Ex. A car air freshener is hanging from a rearview mirror. The air freshener weighing 0.150 N hangs on its string. When the car turns a corner, a horizontal force is exerted at a 40.0o angle. What is the magnitude of the tension on the air freshener’s string? 40o 0.150 N Ex. 0.150 N 40o 40o 0.150 N Homework! ◼P 289 #1ac ◼ P 292 #1aceg 23