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Regents Physics. Agenda Review chapter 6 test Start chapter 7: Forces in 2D HW:. Equilibrium and the Equilibrant. An object is in equilibrium when the net force on it is zero Zero net forces do not cause accelerations
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Regents Physics • Agenda • Review chapter 6 test • Start chapter 7: Forces in 2D • HW:
Equilibrium and the Equilibrant • An object is in equilibrium when the net force on it is zero • Zero net forces do not cause accelerations • In terms of vectors, equilibrium occurs when the resultant of three or more forces equals a net force of zero
Equilibrium • We use basic vector addition to determine if the resultant makes a closed triangle..thus a zero net force resulting in equilibrium
Finding the Equilibrant • Suppose two forces act on a system and the resultant is not zero…how could you find a third force, that when added to the other two, would add to zero? • Such a force, one that produces equilibrium, is called the equilibrant
Finding the Equilibrant • To find the equilibrant, move the move the forces and draw the resultant • The equilibrant is equal in magnitude to the resultant but opposite in direction B A Equilibrant
Practice Problem • A 168 N sign is supported in a motionless position by two ropes that each make 22.5 angles with the horizontal. What is the tension in the ropes? FA FB + x Fg Fnety = 0, so.. FAy + FBy – Fg = 0 FAsin + FBsin - Fg = 0 2FA sin = Fg FA = Fg = 168 N = 220 N 2sin 22.5 Fnet = 0, so.. –FAx + FBx = 0 -FAcos + FBcos = 0 FA = FB
Homework • Pg. 151-152 #1,2 • Pg. 171 #30,31 • SHOW ALL WORK