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 |F g |=m book g |F N |

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