Constant & Changing Motion

1. Constant & Changing Motion

2. Reference Point A fixed point from which direction is defined. The reference point can be anything.

3. Distance The length traveled measured from start to finish. Use meters!!!

4. Example #1 A car drives 4 meters north, 3 meters south, then 5 meters north. What’s its total distance driven? D = 4m + 3m + 5m D = 12m

5. Direction Represented by using : (+) or (-) signs Up or Down Right or Left Forward or Backward North, South , East or West

6. Position Where something is, relative to the reference point.

7. Displacement The net difference between the starting point and the ending point. Dd = dfinal – dinitial

8. Example #2 A car drives 4 meters north, 3 meters south then 5 meters north. What’s its displacement? Δd = 9m north – 3m south Δd = 6m north These are the vectors that we’ve been practicing!

9. Time Interval The difference between two clock readings t = tfinal – tinitial Use seconds!!!

10. Speed Total distance traveled divided by the total time elapsed. speed = distance/time

11. Average Velocity ( Vavg) Total distance traveled divided by the total time elapsed. Vavg = Dd/Dt Units: m/s Magnitude (size) and direction

12. Δt includes ALL time, whether you were moving or not! Average Velocity 1 second 2 minutes 3 seconds 1 mile 2 miles 2 miles home Dairy Queen 4 hr. EXXON 3 hr. LHS 5 miles Δt = 1 sec + 14400 sec + 120 sec + 10800 sec + 3 sec Δt = 25324 sec (x 1 hr / 3600 sec = 7.03 hr) Vavg = 5 mi / 7.03 hr Vavg = 0.71 mi/hr

13. What is the difference between speed and velocity? • Velocity is a vector quantity (magnitude & direction) • Speed represents the magnitude of velocity (scalar quantity)

14. Instantaneous Velocity (V) • Velocity at onepoint • Δd and Δt are very, very, very, very……small!

15. Constant Velocity • If a body is moving at a constant velocity, the velocity never changes between intervals. • Doesn’t happen often in real life! • Ex: V = 10 m/s V = 10 m/s V = 10 m/s

16. Changing Velocity • Here, the velocity changes between intervals. • Ex: V = 10 m/s V = 15 m/s V = 20 m/s

17. Acceleration • Acceleration is the change in velocity over time. • Average acceleration (aavg ) = change in velocity time spent • aavg = ΔV / Δt • Units: (m/s) m s s2

18. Acceleration Example #1 Δt = 2 sec • Find aavg. Vi = 10 m/s Vf = 40 m/s aavg = 40 – 10 m/s 2 s aavg = 15 m/s2 *This means that the object’s velocity increases 15m/s every second!

19. Acceleration Example #2 Δt = 2 sec • Find aavg. Vi = 40 m/s Vf = 10 m/s aavg = 10 – 40 m/s 2 s aavg = -15 m/s2 *This means that the object’s velocity decreases 15m/s every second!

20. Acceleration Example #3 Δt = 2 sec • Find aavg. Vi = 40 m/s Vf = 40 m/s aavg = 40 – 40 m/s 2 s aavg = 0 m/s2 *This means that the object’s velocity is constant!

21. Four Basic Equations of Physics • Conditions: • One-dimensional motion • Constant acceleration

22. Four Basic Equations of Physics • Vf = Vi + at • d = Vi t + ½ at2 • 2ad = Vf2 – Vi2 • Vf + Vi 2 d = t