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I believe that a scientist looking at nonscientific problems is just as dumb as the next guy. -Richard Feynman Nobel Prize in Physics, 1965. Skill Goal for Chapter 4. 0. FBDs are only done in inertial (non-accelerating) frames of reference
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I believe that a scientist looking at nonscientific problems is just as dumb as the next guy.-Richard FeynmanNobel Prize in Physics, 1965
Skill Goal for Chapter 4 0. FBDs are only done in inertial (non-accelerating) frames of reference Use to figure out if any forces are missing, and what forces (or components) have to balance Include on forces ON a body, not forces exerted BY a body Use 3rd law (“equal and opposite reaction force” to help get forces on different bodies Note: Acceleration is not a force. Draw a correct free body diagram (FBD) for every object in a described scenario
For which scenario is FN larger?Choose A, B or C: FN is the same for both. For which scenario is Ff larger? Choose A, B, or C: Ff is the same for both.
2. Include only forces ON the body of interest When I push on a wall and stand at a steep angle, what force shown should not be included in a FBD of me? My weight, mg The normal force from the floor My push on the wall Friction with the floor What can you conclude about the push of the wall on me (Fw) and theforce of friction from the floor (Ff)? Ff > Fw D. Either A or B Ff = Fw E. Either B or C Ff < Fw
3rd Law: “Equal and Opposite” As I stand still, not accelerating, what is the “equal and opposite” reaction force to the force of gravity on me (that is, my weight)? The floor pushing up on me My gravitational pull on the Earth Neither of these.