Create a FBD that represents the situation below 2 ropes are holding the object up and the object is motionless F g (E, B) F t1 (R, B)F t2 (R, B) Should the forces be balanced? Yes, because the object is motionless (constant velocity) Therefore, net force = 0 But this is different than any of the other problems we have done because for the first time, we’ve encountered a scenario where it’s not completely obvious to the eye exactly how the forces balance Balanced (obvious to the eye) Balanced (not so obvious to the eye)

= + 2-D force vector (up & to the right) Any vector directed in 2 dimensions can be thought of as having an influence in 2 different directions Made up of 2 parts Each part of a 2-D vector is known as a component vector The combined influence of the 2 components is equal to the influence of the single 2-D vector Therefore, we can replace the 2-D vector with the component vectors Component vectors 2 horizontal component vectors cancel (balanced) 2 vertical component vectors cancel downward vector (balanced) Much more obvious to the eye how the forces balance

Now try to create the FBD of this situation Object is motionless on an incline F g (E, B) F N (R, B) F f (R, B) Remember, normal force is perpendicular to surface Remember, friction force is parallel to surface We know that the force should balance since the object is motionless (constant velocity) Net force = 0 F g (E, B) F N (R, B) F f (R, B) Fg perp. Fg parallel

Object slides without friction We know that the forces must be unbalanced because the problem does not state that the object is going at a constant velocity We know from past experience that objects going down ramp accelerate Net force not equal to 0 F N (T, B) F g (E, B) Fg F net = 0 Fg By displaying this, we are 100% sure the force that is responsible for this accelerated motion and in what direction VERY IMPORTANT FOR OUR UNDERSTANDING OF MOTION!