PHYS 100: Lecture 4 - University of Illinois Urbana-Champaign

[Pages:18]PHYS 100: Lecture 4

PROJECTILE MOTION

v0

Velocity of Train vT

y(m)

1.4 1.2

1 0.8 0.6 0.4 0.2

0 0

5

10

15

x(m)

y = (v0/vT) x ? (g/2vT2)x2

Physics 100 Lecture 4, Slide 1

Music

Who is the Artist?

BB

A) Miles Davis B) Wynton Marsalis C) Chris Botti D) Nina Simone E) Chet Baker

West Coast "cool" jazz from the 50's In honor of Valentine's Day next week:

His definitive version of My Funny Valentine Hypnotizing voice....

DVD Must-See: Twilight of his career/life Van Morrison does "Send in the Clowns"

Physics 100 Lecture 4, Slide 2

POINTS POINTS POINTS

UNDERSTANDING is the GOAL; POINTS are what we give to get you to do the work

PERFORMANCE

QUIZ EXAM (MIDTERM) FINAL

Phys 100 Fall 2010 Data

EFFORT

DISC HW LECT (PL,CP,LECT)

What are the takeaway messages from this graph? ? A and B students are indistinguishable on EFFORT (>95% avg) ? C and D students do not put in the same effort (70-80%) ? A and B students are distinguished by QUIZ and EXAM grades ? C and D students do poorly on exams (esp quizzes)

NOTE: Performance on Quizzes is your best indicator of your CURRENT understanding

Physics 100 Lecture 4, Slide 3

How To Do Homeworks

? Interactive Examples

REPEAT OF SLIDE FROM LEC 1

? These problems help you develop a "concept-based" problem solving approach ? If you can't calculate the answer to the problem, select the Help Button ? You get another question to help you develop your Plan ! ? Eventually, we "give away the store": This is an "Example" !!!

Physics 100 Lecture 4, Slide 4

THE BIG IDEAS

NOTE: THE BIG IDEAS ARE ALWAYS GIVEN IN THE LAST SLIDE

1. Motion described as 1-D freefall in one frame is described as "projectile motion" in all other frames.

2. Description of projectile motion is superposition of x and y motions a) Constant velocity in x (horizontal) b) Constant acceleration in y (vertical)

Physics 100 Lecture 4, Slide 5

THE PLAN FOR TODAY

1. The Plan is to build to an understanding of the Battleship CheckPoint 2. How will we do this?

a) We will do clicker questions whose explanations will feature equations

b) The purpose is not to memorize these equations but to see how you can REASON with equations !!!

Physics 100 Lecture 4, Slide 6

Ball on a Cart

DEMO: Ball is ejected straight up from a cup in a cart moving at constant velocity. When it falls back , will it land (A) in back of the cup (B) in the cup (C) in front of the cup

v0

A

C

B

v

BB

This is THE POINT: Descriptions of same motion from two different reference frames

Cart frame: motion is 1-D free fall: ball goes up, stops, and comes straight back down

vy = v0 - gt

y

=

v0t

-

1 2

gt

2

yC

vx = 0

x=0

xC

Ground frame: motion is 2-D projectile: ball follows parabolyicG trajectory

vy = v0 - gt

y

=

v0t

-

1 2

gt

2

vx = v

x = vt

Physics 100 Lecture 4, SxliGde 7

Ball on a Cart II

DEMO: Ball is ejected straight up from a cup in a cart moving at constant acceleration. When it falls back , will it land (A) in back of the cup (B) in the cup (C) in front of the cup

v0

A

C

B

a

BB

WHAT'S THE DIFFERENCE?

Ground frame: motion OF BALL is 2-D projectile: parabolic trajectory motion OF BALL in x-direction is motion at constant velocity motion OF CART in x-direction is motion with increasing velocity

xBALL = vt

xCART

= vt +

1 2

at

2

Physics 100 Lecture 4, Slide 8

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