Physics 203 – College Physics I Department of Physics – The Citadel Physics 203 College Physics I Fall 2012 S. A. Yost Chapter 2 Motion in 1 Dimension – Part 2

Physics 203 – College Physics I Department of Physics – The Citadel Today’s Topics & Announcements 1. Constant Velocity Motion 2. Non-Constant Velocity Motion - Graphical 3. Constant Acceleration Motion and Falling. There is a presentation by Dr. Adelman at 6:30 here this evening: Great Astronomical Images. Free DVDs will be distributed after the talk. You can get some extra participation credit for attending. See me there to be checked off, if you attend.

Physics 203 – College Physics I Department of Physics – The Citadel Tuesday’s Assignment Read Ch. 2, sec. 6 – 7. We will talk some about section 8, but what we do in class is all you will need. A quiz on sections 1 – 7 using i>clickers should be anticipated, since we are not having one today. Also, start reading Ch. 3: at least through sec 2, and to sec. 4 if you can. Problem Set HW2 is open and due next Thursday. It is mostly on Chapter 2, but includes some trigonometry practice for Chapter 3.

Physics 203 – College Physics I Department of Physics – The Citadel Constant Velocity Equation x = x 0 + v t gives the position as a function of time of an object starting at position x 0 and traveling with velocity v.

Physics 203 – College Physics I Department of Physics – The Citadel Constant Velocity Motion A cart goes from x = 2 m at t = 1 s to x = 8 m at t = 3 s at constant velocity. Draw a graph of the motion. What is the velocity? v = = = 3 m/s  x 6 m  t 2 s x (m) t (s)

Physics 203 – College Physics I Department of Physics – The Citadel Constant Velocity Motion Where was the cart at t = 0? Linear equation: x = x 0 + v t Evaluate at any point: 2 m = x 0 + (3 m/s)(1 s) Solve for x 0 : x 0 = 2 m – 3 m = – 1 m x (m) t (s) v = 3 m/s intercept

Physics 203 – College Physics I Department of Physics – The Citadel Piecewise Linear Motion x (m) t (s) A B C D E What is the displacement from 0 to 8 sec?  x  1 m.

Physics 203 – College Physics I Department of Physics – The Citadel Piecewise Linear Motion x (m) t (s) A B C D E What is the average velocity from 0 to 8 sec? v  m/s 

Physics 203 – College Physics I Department of Physics – The Citadel Piecewise Linear Motion x (m) t (s) A B C D E What is the distance traveled from 0 to 8 sec? d = m = 21 m Distance is the total path-length traveled.

Physics 203 – College Physics I Department of Physics – The Citadel Position vs Time Graph x (m) t (s) A B C D E Where is the object at rest? C

Physics 203 – College Physics I Department of Physics – The Citadel Position vs Time Graph x (m) t (s) A B C D E What is the instantaneous velocity at t =1s? v =4 m/s Instantaneous velocity is defined at one time What is the instantaneous velocity at t =3s? v = – 2 m/s

Physics 203 – College Physics I Department of Physics – The Citadel Position vs Time Graph x (m) t (s) A B C D E Where does the object have the greatest instantaneous speed? D Speed is distance traveled divided by the time.

Physics 203 – College Physics I Department of Physics – The Citadel Position vs Time Graph x (m) t (s) A B C D E What is that speed?|v|=7.0 m/s

Physics 203 – College Physics I Department of Physics – The Citadel Position vs Time Graph x (m) t (s) A B C D E What is the average velocity for the first 4 seconds? v = 4m/4s = 1.0 m/s 

Physics 203 – College Physics I Department of Physics – The Citadel Position vs Time Graph x (m) t (s) A B C D E What is the average speed for the first 4 seconds? |v| = (8+4)m/4s = 3.0 m/s

Physics 203 – College Physics I Department of Physics – The Citadel Displacement vs Distance You and your dog go for a walk to a park. You walk in a straight line while your dog runs back and forth. When you and your dog arrive at the park, who has the greater displacement? A. You B. Dog C. Same Who had the greater average velocity? A. You B. Dog C. Same Who had the greater average speed? A. You B. Dog C. Same

Physics 203 – College Physics I Department of Physics – The Citadel Speed vs Velocity Which does the odometer on your car measure? A. Distance B. Displacement Which does the speedometer on your car measure? A. Speed B. Velocity Is speed ever negative? A. Yes B. No Is velocity ever negative? A. Yes B. No