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PHYS16 – Lecture 9

PHYS16 – Lecture 9. Force and Newton’s Laws September 27, 2010. Hey, how come we’re not moving?. Review. Review: 1D & 2D Motion. For projectile motion, the angle that gives you the maximum range is: A) 90 degrees B) 45 degrees C) 15 degrees D) 55 degrees. Review: 1D & 2D Motion.

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PHYS16 – Lecture 9

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  1. PHYS16 – Lecture 9 Force and Newton’s Laws September 27, 2010 Hey, how come we’re not moving?

  2. Review

  3. Review: 1D & 2D Motion • For projectile motion, the angle that gives you the maximum range is: A) 90 degrees B) 45 degrees C) 15 degrees D) 55 degrees

  4. Review: 1D & 2D Motion • For projectile motion, the angle that gives you the maximum height is: A) 90 degrees B) 45 degrees C) 15 degrees D) 55 degrees

  5. Review: 1D & 2D Motion • When analyzing the motion of an object, motion in x is ________ motion in y. A) related to B) perpendicular C) coupled to D) independent of

  6. Review: 1D & 2D Motion • Constant, non-zero acceleration in y leads to displacement in y that is A) linear B) parabolic C) constant D) exponential

  7. Force

  8. Key Concepts: Force • Force • Definition and Types • Center of Mass • Free Body Diagrams • Newton’s Laws • Friction

  9. Force - Definition • A push or a pull that can change an object’s motion Contact Forces – need to contact object Tension – reaction force along rope away from object Compression – a push Normal – reaction force that is perpendicular to surface Friction – breaking of bonds along surface that resist motion Biological – forces applied by people Fundamental Forces – Long range Gravity – attraction btw masses Electromagnetic – attraction/repulsion btw charges Strong – holds protons & neutrons in nucleus Weak – responsible for neutrino/beta decay

  10. Most Common Forces • Gravity • Normal • Tension • Friction

  11. Forces act at: • Contact forces act at the point of contact • If we can assume the object is a point object then we can draw these forces acting at the center of mass • Long range forces act at the center of mass

  12. Center of Mass • Center of mass is geometric center of object weighted by the object’s mass distribution • Assume density is the same throughout following objects and find center of mass:

  13. Free Body Diagrams • Simplified picture of the object + the forces acting on the object • Relevant axes are defined • Forces are drawn at the point of action • Ex. Book on a table |FN| |Fg|=mbookg

  14. Free Body Diagram Practice • Cat falling out of window • Person pushing on wall • Car moving down highway • Block on incline

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