DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS

Transcription

1 DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS

2 LSN 2-1, KINEMATICS

3 Questions From Reading Activity?

4 Assessment Statements Topic 2.1, Kinematics: Define displacement, velocity, speed, and acceleration. Explain the differences between instantaneous and average values of speed, velocity and acceleration. Outline the conditions under which the equations for uniformly accelerated motion may be applied.

5 Assessment Statements Topic 2.1, Kinematics: Identify the acceleration of a body falling in a vacuum near the Earth s surface with the acceleration g of free fall. Solve problems involving the equations of uniformly accelerated motion. Describe the effects of air resistance on falling objects.

6 Assessment Statements Topic 2.1, Kinematics: Draw and analyze distance-time graphs, displacement-time graphs, velocity-time graphs, and acceleration-time graphs. Determine relative velocity in one and in two dimensions.

7 Objectives Describe the difference between distance and displacement. State the definitions of velocity, average velocity, speed, and average speed. Solve problems of motion in a straight line with constant velocity. Use graphs in describing motion.

8 Objectives Appreciate that different observers belonging to different frames of reference can give differing but equally valid descriptions of motion. Understand that the slope of a displacement-time graph is the velocity is the velocity and that the area under a velocity-time graph is the change in displacement.

9 Introductory Video

10 Displacement The displacement of a point from a given reference point will be given by a magnitude and a direction. The magnitude indicates the distance from the reference point to the given point The direction may be either a sign (+ or -) or a degree measurement from a defined a coordinate plane centered at the reference point.

11 Displacement The displacement of a point from a given reference point will be given by a magnitude and a direction. The magnitude indicates the distance from the reference point to the given point The direction may be either a sign (+ or -) or a degree measurement from a defined a coordinate plane centered at the reference point.

12 Displacement Example 1 P O The displacement of point P from point O is 10m at 40º.

13 Displacement Example 2 P O The displacement of point P from point O is 10m

14 Displacement Example 3 The displacement of point O from point P is -10m P O

15 Displacement Example 4 The displacement of point O from point P is 10m at 220º or, 10m at 40º below the negative x-axis. P O

16 Displacement Example 5 From a reference point, a completely fictional character named Ashley moves 6m left and 3m down. What is her distance and displacement?

17 Displacement Example 5 From a reference point, a completely fictional character named Ashley moves 6m left and 3m down. What is her distance and displacement? Distance is based on total length travelled so, d = 6m + 3m = 9m Displacement is based on length from initial position to final position. What do you use for magnitude?

18 Displacement Example 5 From a reference point, a completely fictional character named Ashley moves 6m left and 3m down. What is her distance and displacement? Displacement is based on length from initial position to final position. Use Pythagorean theorem for magnitude. c 2 a 2 b 2 c m

19 Displacement Example 5 From a reference point, a completely fictional character named Ashley moves 6m left and 3m down. What is her distance and displacement? What about direction?

20 Displacement Example 5 From a reference point, a completely fictional character named Ashley moves 6m left and 3m down. What is her distance and displacement? What about direction? Use tangent. tan tan opp adj

21 Displacement vs. Distance Displacement is the distance from initial position to final position regardless of path taken. Δx = x x 0 Distance is total length travelled along path taken. Displacement is a vector (magnitude and direction). Distance is a scalar (magnitude only).

22 Speed Average speed is equal to the total distance travelled divided by the total time v s S T Instantaneous speed is like measuring your speed in a split second. Mathematically it is, v lim T 0 S T

23 Velocity Average velocity is equal to displacement divided by time v x t Similarly, instantaneous velocity is like measuring the velocity in a split second. x t x t 0 0 v lim t 0 x t

24 Velocity When we just use the term velocity the implication is that it is constant, i.e. not increasing (acceleration) or decreasing (deceleration) v x x x 0 t t t 0

25 Speed vs. Velocity Speed Based on distance A scalar quantity (magnitude only) Always positive Velocity Based on displacement A vector quantity (magnitude and direction) Can be positive or negative

26 Speed vs. Velocity For both, it is important to know whether they are constant, average, or instantaneous. I.e., you must know if there is any acceleration

27 Speed vs. Velocity An athlete runs one lap around an Olympic track (400m) in 50 seconds. What is his speed and velocity?

28 Speed vs. Velocity An athlete runs one lap around an Olympic track (400m) in 50 seconds. What is his speed and velocity? S 400m v s T 50s 8 m s x x 0m v 0 0 t t 0 50s

29 How far? Suppose you want to know how far you have travelled in a certain time, t (t 0 = 0)?

30 How far? Suppose you want to know how far you have travelled in a certain time, t (t 0 = 0)? x v t vt x x t 0 0 x 0 x t x 0 x 0 vt x x x 0 vt

31 Frame of reference Frame of reference refers to the origin from which measurements are made. A student in a classroom appears to be stationary To an observer on the moon, the student appears to be rotating about the earth s axis even as the earth is itself is moving away as the moon orbits the earth To an observer on the sun, the student is rotating about the earth s axis as the earth orbits the sun To an observer in another galaxy, the student is rotating about the earth s axis as the earth orbits the sun and the whole galaxy is moving away To the teacher, the student is a lump of coal

32 Frame of reference A fictitious student named Srihar is riding on a train travelling at 10m/s. Another fictitious student named Andreas is standing still, watching the train go by. According to Andreas, what is Srihar s velocity? 10 m/s

33 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. According to Andreas, what is Srihar s velocity? 10 m/s 10m/s from left to right

34 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. According to Srihar, what is his velocity in relation to the train? 10 m/s

35 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. According to Srihar, what is his velocity in relation to the train? 10 m/s 0m/s, stationary

36 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. According to Srihar, what is Andreas velocity? 10 m/s

37 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. According to Srihar, what is Andreas velocity? 10 m/s 10m/s from left to right

38 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. Srihar moves to the back of the train at 3m/s. According to Srihar, what is his velocity in relation to the train? 10 m/s

39 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. Srihar moves to the back of the train at 3m/s. According to Srihar, what is his velocity in relation to the train? 10 m/s 3m/s, from left to right

40 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. Srihar moves to the back of the train at 3m/s. According to Srihar, what is Andreas velocity? 10 m/s

41 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. Srihar moves to the back of the train at 3m/s. According to Srihar, what is Andreas velocity? 10 m/s 7m/s, from left to right

42 Frame of reference A fictitious student named Jamal is riding on a train travelling at 10m/s. Another fictitious student named Reid is standing still, watching the train go by. According to Andreas, what happens next? 10 m/s

43 Next

44 Summary Review Can you describe the difference between distance and displacement? Can you state the definitions of velocity, average velocity, speed, and average speed? Can you solve problems of motion in a straight line with constant velocity? Can you use graphs in describing motion?

45 Objectives Do you appreciate that different observers belonging to different frames of reference can give differing but equally valid descriptions of motion? Do you understand that the slope of a displacement-time graph is the velocity is the velocity and that the area under a velocity-time graph is the change in displacement?

46 Assessment Statements Topic 2.1, Kinematics: Define displacement, velocity, speed, and acceleration. Explain the differences between instantaneous and average values of speed, velocity and acceleration. Outline the conditions under which the equations for uniformly accelerated motion may be applied.

47 Assessment Statements Topic 2.1, Kinematics: Identify the acceleration of a body falling in a vacuum near the Earth s surface with the acceleration g of free fall. Solve problems involving the equations of uniformly accelerated motion. Describe the effects of air resistance on falling objects.

48 Assessment Statements Topic 2.1, Kinematics: Draw and analyze distance-time graphs, displacement-time graphs, velocity-time graphs, and acceleration-time graphs. Determine relative velocity in one and in two dimensions.

49 QUESTIONS?

50 Homework #1-12