2. Catalyst 1. What is the difference between speed and velocity? 2. Put these objects in order from slowest to fastest: ● Peregrine falcon ● Cheetah ● Human ● Car (at the highway speed limit) ● Mako shark ● Ocean wave ● Maglev train

3. Motion & Forces II. Describing Motion  Motion  Speed & Velocity  Acceleration

4. A. Motion Problem:  Is your desk moving? We need a reference point...  nonmoving point from which motion is measured

5. A. Motion Motion  Change in position in relation to a reference point. Reference point Motion

6. A. Motion Problem: You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward. You have mistakenly set yourself as the reference point.

7. B. Speed & Velocity Speed  rate of motion  distance traveled per unit time s d t

8. B. Speed & Velocity Velocity  speed in a given direction  can change even when the speed is constant! v d t Units: D=meter t-=seconds V=m/s

9. B. Speed & Velocity Instantaneous Speed  speed at a given instant Average Speed

10. B. Speed & Velocity Problem:  A storm is 10 km away and is moving at a speed of 60 km/h. Should you be worried?  It depends on the storm’s direction!

11. More Practice Try problems 1-5 on the Speed Practice Problems sheet on my website on a separate sheet of paper. Use the guess method we practiced when we worked on density.

12. How do distance and displacement differ? Distance is the total distance of the path travelled. Displacement- measured from start point to ending point in one line. (if you start & stope in the same spot, displacement =0.

13. Graphing Motion Graphing Motion slope = steeper slope = straight line = flat line = Distance-Time Graph A B faster speed constant speed no motion speed

14. Graphing Motion Graphing Motion Who started out faster?  A (steeper slope) Who had a constant speed? AA Describe B from 10-20 min.  B stopped moving Find their average speeds.  A = (2400m) ÷ (30min) A = 80 m/min  B = (1200m) ÷ (30min) B = 40 m/min  See pg 334 in text  See pg 335 Distance-Time Graph A B

15. Graphing Motion Graphing Motion Acceleration is indicated by a curve on a Distance-Time graph. Changing slope = changing velocity

16. Solve- not in your notes The diagram below shows the position of a cross-country skier at various times. At each of the indicated times, the skier turns around and reverses the direction of travel. In other words, the skier moves from A to B to C to D. Use the diagram to determine distance traveled by the skier during these three minutes. Can you determine the displacement? The skier covers a distance of (180 m + 140 m + 100 m) = 420 m and has a displacement of 140 m, rightward

17. A football coach paces back and forth along the sidelines. The diagram below shows several of coach's positions at various times. At each marked position, the coach makes a "U-turn" and moves in the opposite direction. In other words, the coach moves from position A to B to C to D. W hat is the coach's resulting displacement and distance of travel? The coach covers a distance of (35 yds + 20 yds + 40 yds) = 95 yards and has a displacement of 55 yards, left. not in your notes

18. Calculations Calculations Your neighbor skates at a speed of 4 m/s. You can skate 100 m in 20 s. Who skates faster? GIVEN: d = 100 m t = 20 s v = ? WORK : v = d ÷ t v = (100 m) ÷ (20 s) v = 5 m/s You skate faster! v d t

19. Calculations Calculations Sound travels 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for you to hear it? GIVEN: v = 330 m/s d = 1km = 1000m t = ? WORK : t = d ÷ v t = (1000 m) ÷ (330 m/s) t = 3.03 s v d t

20. C. Acceleration Acceleration  the rate of change of velocity  change in speed or direction A : acceleration(m/s 2 ) V f : final velocity (m/s) V i : initial velocity (m/s) T : time (sec) a v f - v i t

21. 3 ways an object can accelerate 3 ways an object can accelerate 1. Positive acceleration=“speeding up” 2. Negative acceleration (aka. Deceleration= “slowing down” 3. Changing direction- traveling around a curve with constant speed.

22. Free Fall Objects that fall in air towards Earth, due to gravity. Objects fall at the rate of 9.8m/s 2 (acceleration due to gravity= 9.8m/s 2) T=1s V=9.8 m/s T=2s V=19.6 m/s T=3s V=29.4m/s

23. Terminal Velocity the highest velocity that will be reached by a falling object.

24. Graphing Motion Graphing Motion Speed-Time Graph slope = straight line = flat line = acceleration  +ve = speeds up  -ve = slows down constant accel. no accel. (constant velocity)

25. Graphing Motion Graphing Motion Speed-Time Graph Specify the time period when the object was... slowing down  5 to 10 seconds speeding up  0 to 3 seconds moving at a constant speed  3 to 5 seconds not moving  0 & 10 seconds

26. Calculations Calculations A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration? GIVEN: v i = 10 m/s t = 3 s v f = 32 m/s a = ? WORK : a = ( v f - v i ) ÷ t a = (32m/s - 10m/s) ÷ (3s) a = 22 m/s ÷ 3 s a = 7.3 m/s 2 a v f - v i t

27. Calculations Calculations How long will it take a car traveling 30 m/s to come to a stop if its acceleration is -3 m/s 2 ? GIVEN: t = ? v i = 30 m/s v f = 0 m/s a = -3 m/s 2 WORK : t = ( v f - v i ) ÷ a t = (0m/s-30m/s)÷(-3m/s 2 ) t = -30 m/s ÷ -3m/s 2 t = 10 s a v f - v i t

28. B. Momentum p = mv p:momentum (kg ·m/s) m:mass (kg) v:velocity (m/s) m p v All objects have mass; so if an object is moving, then it has momentum

29. Law of Conservation of Momentum Momentum is not created nor destroyed during a crash. if no net force acts on a system, then the total momentum of the system does not change. In a closed system, the loss of momentum of one object equals the gain in momentum of another object-momentum is conserved.