Welcome back to PHY101: Major Concepts in Physics I. Photo: J. M. Schwarz

Transcription

1 Welcome back to PHY101: Major Concepts in Phsics I Photo: J. M. Schwarz

2 Announcements Course Website: jmschwarztheorgroup.org/ph101/ HW on Chapter is due at the beginning of lecture on Wednesda. HW 3 on Chapter 3 will be assigned soon. Please go to the course website to access it once it is posted. HW 3 is due on Wednesda, September 19, at the beginning of lecture. Labs begin this week, so please attend lab. Your grade depends on it. To purchase the ebook for the course, see the sllabus on the course website.

3 Three Big Questions (Chapter ) How does one define position, displacement, elocit, and acceleration? How does one describe motion along a line with constant elocit? How does one describe motion along a line with constant acceleration?

4 4 Visualizing Motion Along a Line with Constant elocit a t a t a t i f i f i i f D + D - D D + D - D 1 For constant elocit, the kinematic equations are: 0

5 5 Visualizing Motion Along a Line with Constant Acceleration a t a t a t i f i f i i f D + D - D D + D - D 1 For constant acceleration, the kinematic equations are: a, a, f i t + D D Also:

6 Check out the equation sheet on the course website!

7 Clicker question 1 A ball is thrown straight up into the air. Ignore air resistance. While the ball is in the air its acceleration (a) increases. (b) is zero. (c) remains constant. (d) decreases on the wa up and increases on the wa down.

8 Clicker question 1 A ball is thrown straight up into the air. Ignore air resistance. While the ball is in the air its acceleration (a) increases. (b) is zero. (c) remains constant. (d) decreases on the wa up and increases on the wa down.

9 It s Demo Time!

10 Phsics Problem Soling 1 DAP Draw a picture KNU Knowns and unknowns 3 EQN Equation(s) 4SSF Sole smbolicall first 5CYA Check our answer 6PIK Plug in knowns

11 Eample: You throw a ball into the air with speed 15.0 m/s; how high does the ball rise? i Gien: i m/s; a -9.8 m/s a To calculate the final height, we need to know the time of flight. D i Dt + 1 a Dt Time of flight from: f i + a Dt 11

12 Eample: You throw a ball into the air with speed 15.0 m/s; how high does the ball rise? i Knowns: i m/s; a -9.8 m/s a To calculate the final height, we need to know the time of flight. D i Dt + 1 a Dt Time of flight from: f i + a Dt 1

13 Eample continued: The ball rises until f 0. f Dt - i a + i a Dt m/s m/s 1.53 sec The height: D i Dt + ( )( ) ( 15.0 m/s 1.53 s m/s )( 1.53 s) 11.5 m 1 a Dt 1 13

14 Clicker question Two balls are thrown from the top of a building. One is thrown up and the other is thrown down, both with the same initial speed. What are their speeds when the hit the street? A. the are traeling at the same speed B. the one thrown down is traeling faster C. the one thrown up is traeling faster D. it depends on the height of the building

15 Clicker question Two balls are thrown from the top of a building. One is thrown up and the other is thrown down, both with the same initial speed. What are their speeds when the hit the street? A. the are traeling at the same speed B. the one thrown down is traeling faster C. the one thrown up is traeling faster D. it depends on the height of the building

16 Phsics Problem Soling 1 DAP Draw a picture KNU Knowns and unknowns 3 EQN Equation(s) 4SSF Sole smbolicall first 5CYA Check our answer 6PIK Plug in knowns

17 Eample (tet problem.57): A penn is dropped from the obseration deck of the Empire State Building 369 m aboe the ground. With what elocit does it strike the ground? Ignore air resistance. 369 m a Knowns: i 0 m/s, a -9.8 m/s, D -369 m Unknown: f Use: f i + a D a D f a D 17

18 Eample (tet problem.57): A penn is dropped from the obseration deck of the Empire State Building 369 m aboe the ground. With what elocit does it strike the ground? Ignore air resistance. 369 m a Knowns: i 0 m/s, a -9.8 m/s, D -369 m Unknown: f Use: f i + a D a D f a D 18

19 Eample continued: f a D ( m/s )(- 369) m 85.0 m/s (downward) How long does it take for the penn to strike the ground? Gien: i 0 m/s, a -9.8 m/s, D -369 m Unknown: Dt D Dt i Dt + D a 1 a D D t a t 8.7 sec 1 19

20 Eample continued: f a D ( m/s )(- 369) m 85.0 m/s (downward) How long does it take for the penn to strike the ground? Gien: i 0 m/s, a -9.8 m/s, D -369 m Unknown: Dt D Dt i Dt + D a 1 a D D t a t 8.7 sec 1 0

21 Fender benders

22 And now on to Chapter 3, Section 5.

23 3.5 Motion in a Plane. 3

24 3.5 Motion in a Plane. 4

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26 Two Big Questions (Chapter 3, Sec. 5) How does one define position, displacement, elocit, and acceleration in the plane? How does one describe motion in the plane with constant acceleration?

27 It s demo time!

28 Clicker question 3 Will the two cubes hit the floor at the same time? A. Yes B. No

29 Clicker question 3 Will the two cubes hit the floor at the same time? A. Yes B. No

30 The ertical and horizontal motions each proceed independentl, as if the other motion was not present. Page 71 of tetbook

31 Visualizing Motion in a Plane with Constant Acceleration For constant acceleration the kinematic equations in the plane are: D D f f - i - i i Dt + a Dt 1 a Dt Δ f i i Δt + 1 a Δt Δ f i aδt f i + a D f i + aδ 31

32 3.5 Motion in a Plane with Constant Acceleration What is the motion of a struck baseball? Once it leaes the bat (if air resistance is negligible) onl the force of grait acts on the baseball. 3

33 The baseball has a 0 and a -g, it moes with constant elocit along the -ais and with nonzero, constant acceleration along the -ais. 33

34 Clicker question 4 A ball thrown into the air follows a parabolic trajector. At the highest point in the trajector A. both the elocit and the acceleration are zero. B. the elocit is zero, but the acceleration is not zero. C. neither the acceleration nor the elocit are zero. D. the acceleration is zero but the elocit is not zero.

35 Clicker question 4 A ball thrown into the air follows a parabolic trajector. At the highest point in the trajector A. both the elocit and the acceleration are zero. B. the elocit is zero, but the acceleration is not zero. C. neither the acceleration nor the elocit are zero. D. the acceleration is zero but the elocit is not zero.