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Download Quantitative FBDs
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Quantitative FBDs Just like in units 1 & 2, our models (x-t, v-t, a-t graphs) didn’t really mean a whole lot if they couldn’t have predictive power • Because predictive power requires actual numbers (how fast something will be going, how far something has traveled) we need to make sure our FBD models have predictive power as well With 1-D forces, it’s fairly easy 5 kg cat sitting motionless on rug Fg = 5 kg x 10 Fg = 50 N m/s2 Fn = 50 N (must balance Fg) Fn (R, C) 50 N 50 N Fg (E, C) With 2-D forces, we have to do a bit more work to calculate the forces involved • Involves basic trigonometry First, a little intro to basic trig. Sine, Cosine, and Tangent • • 3 main functions in trig Usually shortened as sin, cos, and tan To calculate sin, cos, and tan • Divide the length of one side by another side……but you must know which sides! SOH CAH TOA Find the height of the flag pole and the hypotenuse Find the hypotenuse and the length of the side adjacent (next to) the angle given Let’s apply what we have just learned to a more physics-based question: • An 10 kg object sits motionless on an incline due to friction 300 The 2000 kg elephant is standing motionless on the ramp due to friction. • What is the normal force that the ramp is pushing up on the elephant with? What is the force of friction that prevents the elephant from sliding down?
