i don’t remember class very well. seemed like it went reasonably smoothly and was lots of student...

• I don’t remember class very well. Seemed like it went reasonably smoothly and was lots of student engagement. Need to spend a bit more time on reading x and y values from graph and getting slope. Maybe make them do as a clicker question.

• Here and more later there was lots of confusion about signs of position and velocity and direction. Need to use sign reversal feature of moving man to clarify. See comments on class#3.

Welcome to Physics 1010: The Physics of Everyday Life

Instructors: Carl Wieman and Kathy Perkins

Missed class on Tuesday? Pick up Tuesday’s handouts at the front of the room:

Syllabus (1st 2 pages) & Seating chart.

Please find your assigned seat.

Have a new clicker ….Test it out - push button, find your number No clicker? Bookstore to have more Monday. If no clicker, today only fill in bubble sheet and turn in at end of class.

Motion

Understand motions around us … balls, cars, bikes, people, atoms ….

But before how or why … We need to be able to describe motion… words, graphs, equations

To do: Reading 1.1 & 1.2 (due today)Homework #1 is posted and due at 11:59 PM Tuesday night. Online Surveys (2 links)

Important Notes on Homework: Checkboxes --- Check all that are correct!Numeric Answer --- Enter number only in box … no words or units …

Units either specified question or use selection menu.Numeric Answer --- Either 4000 or 4.0E3. Will not recognize 4.0x10^3m/s = meters/second (not miles/second)

Clicker Question: (don’t click yet … establish locations)a) I have tried logging on to the homework systemb) I will try logging on this afternoonc) I absolutely promise to logon on Friday.d) none of the aboveUSERNAME first initial followed by last name …. kperkinsPASSWORD last 4 digits of ID.

Phys1010 Homepage Info (www.colorado.edu/physics/phys1010) Clicker registration, Reading assignments, Homework assignments

Office Hours & Problem Solving Sessions

Phys help room

G2B87

Phys1010 problem solving sessionin G2B87 or near by. Just look around.

Enter throughG2B90

Regular Weekly Hours (Starts this Thurs.)

Wednesdays: 4-5 pmThursdays: 2-5 pm TODAYFridays: 10am-12pm

and 1-5:30pm

With Carl, Kathy, Zach, Dan, Stephanie, and Jeff.

Special SessionNext Tuesday

3-5:30 pm

Homework too hard to do alone, butok & learn lot when work together.We will help interactions, coach, NOT give answers.

cw kp

Reading quiz. chapters 1.1 and 1.2 (read before class, learn more)

1. The physics topic that is the primary focus of chap. 1.2 isa) the theory of gravityb) how air resistance affects falling objectsc) the motion of dropped or thrown objects d) the relationship between English and metric units of masse) the physics behind how baseball pitchers can throw curve balls

2) If you push on two bowling balls with the same force, but one has half the mass of the other, then … ?

a. both masses accelerate the same b. the low mass ball accelerates faster than the high mass ball.c. the high mass ball accelerates faster than the low mass ball.d. none of the above.

3) If the two bowling balls fell off a table at the same time:a) Both would fall with the same constant velocity all the way to floor.b) The heavy ball would accelerate more rapidly.c) The light ball would accelerate more rapidly.d) Both would fall with the same acceleration.

Do the experiment: about how fast was Prof. Bohn walking? (pick the closest balue)

a) 100 m/s

b) 10 m/s

c) 1 m/s

d) 0.1 m/s

e) 0 m/s

Human MotionDemo 2: Sketch velocity vs. time graph for 1) Person moving away from origin (motion detector) at steady velocity on left. 2) Person moving toward origin (mot. det.) at steady velocity on right.

Vel

ocity

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0

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Vel

ocity

time

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time

away toward


Vel

ocity

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ocity

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-time

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ocity

Vel

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-time

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-time

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ocity

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-time

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A B

C D


Vel

ocity

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ocity

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time

0feet

10-10

Velocity is a vector. Magnitude (length) gives speed. Pointing direction gives sign. (positive or negative)

away toward


Vel

ocity

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ocity

time

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0feet

10-10

Velocity is a vector. Magnitude (length) gives speed. Pointing direction gives sign. (positive or negative)

What is the difference between “speed” and “velocity”?

1. You are driving 60 miles per hour north.

2. You are driving 60 miles per hour.

a. both give your speed, can’t tell your velocity.b. 2. gives speed, 1. gives velocity.c. both are giving your velocity.d. 2 gives velocity, 1. gives your speed.

ans. b. 1. gives speed and direction = velocity. 2. gives only your speed, but since direction not specified, do not know velocity.

if speed is constant 60 mph, can velocity be changing?

yes! driving in circle. direction changing = velocity changing = accelerating!

Human MotionDemo 3: Sketch position vs. time and velocity vs. time graphs for person moving away from origin (motion detector) at twice velocity of Demo #1 and 2.

+

0

-

Pos

ition

time

Vel

ocity

+

0

-

time

Describe in words how the velocity vs time and position vs time graphs change when the speed is twice as fast.

#1

#1


+

0

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ition

time

Vel

ocity

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time

#1

#1

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ition

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#1

#1

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ition

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#1

#1

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ition

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#1

#1

A

DC

B


+

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Pos

ition

time

Vel

ocity

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0

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time

Describe in words how the velocity vs time and position vs time graphs change when the speed is twice as fast.

#1

#1

D

velocity

How does position (distance) vs time relate to velocity vs time?

Velocity graph is slope of position graph.

1 meter

0

-1

pos

ition

timeve

loci

ty

+

0

-

time

2 s 4 s

-0.5 m/s

+0.25 m/s

What does velocity graphlook like?

man walking, with cursors, web demo.

Velocity at 2 s is:a) 1 m/sb) -1 m/sc) 0.5 m/sd) -0.5 m/se) - 1/6 m/s

Velocity (v) = change in position = distance traveled time elapsed time it took

Position = Starting position + change in positionPosition = Starting position + velocity x timex = xinitial + vt

Equations also help us describe and think about motion

V is slope of position vs timegraph

1 meter

0

-1

dis

tan

ce

2 s 4 s

time = 1 secondposition = 1 meter

time = 3 secondposition = 0 meter

Change in Position = -1 meter

Time elapsed = 2 seconds

Velocity = -1 meter = -0.5 m/s 2 seconds

How do you know direction?

What if velocity is changing? … Accelerating

Acceleration (a) = change in velocity time elapsed

Velocity = Starting velocity + change in velocityVelocity = Starting velocity + acceleration x time v = vinitial + at

And now

Position = initial position + (average velocity) x timex = xinitial + vinitial t + ½ at2

And

Distance traveled = (average velocity) x time = vinitial t + ½ at2

Check with moving man graphs, or cart data to see if true.

Equations also help us describe and think about motion

A is slope of velocity vs time graph

=vinitial + ½(change in velocity)=vinitial + ½at

Demo 4: Sketch position vs time and velocity vs time graphs for when Moving Man: walks steadily towards the tree for 6 seconds,then stands still for 6 seconds, and then towards the house twice as fast as before for 6 seconds.

Do yours as dashed line, compare with team members then make solid line based on group.

+

0

-P

ositi

on

time

Vel

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time

5 s 10 s 20 s15 s

Vel

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time

5 s 10 s 20 s15 s

Vel

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5 s 10 s 20 s15 s

Vel

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5 s 10 s 20 s15 s

A B

C

Vel

ocity +

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-P

ositi

ontime

5 s 10 s 20 s15 s

D

Demo 4: Sketch position vs time and velocity vs time graphs for when Moving Man: walks steadily towards the tree for 6 seconds,then stands still for 6 seconds, and then towards the house twice as fast as before.

Do yours as dashed line, compare with team members then make solid line based on group.

Vel

ocity

+

0

-

time

+

0

-P

ositi

on time

5 s 10 s 20 s15 s

D

10-10 0 meters -1010 0 meters

Sketch graphs for Moving Man walks from the house to the tree:

+

0

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Pos

ition

time

Vel

ocity +

0

-

time

5 s 10 s 20 s15 s

+

0

-

Pos

ition

time

Vel

ocity +

0

-

time

5 s 10 s 20 s15 s

Choose to define positive direction as towards house.

Choose to define positive direction as towards tree.

a. The position vs time graphs are different; the velocity vs. time graphs are the same.

b. Both the position vs. time and velocity vs. time graphs are different.

c. Both the position vs. time and velocity vs. time graphs are the same.

d. The position vs time graphs are the same. The velocity vs. time graphs are different.

e. I can’t make sense of these graphs.

How do the graphs in these 2 cases compare?

case a. positive towards house. case b. positive towards tree.

10-10 0 meters -1010 0 meters

Sketch graphs for Moving Man walks from the house to the tree:

+

0

-

Pos

ition

time

Vel

ocity +

0

-

time

5 s 10 s 20 s15 s

+

0

-

Pos

ition

time

Vel

ocity +

0

-

time

5 s 10 s 20 s15 s

Choose to define positive direction as towards house.

Choose to define positive direction as towards tree.

notice slopes and velocities

Human Motion

+

0

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Pos

ition

time Vel

ocity

+

0

-

time

Part 1:

Part 2:

Walk this way & take data

Walk this way& take data

a. The position vs time graphs are different; the velocity vs. time graphs are the same.

b. Both the position vs. time and velocity vs. time graphs are different.

c. Both the position vs. time and velocity vs. time graphs are the same.

d. The position vs time graphs are the same. The velocity vs. time graphs are different.

e. I can’t make sense of these graphs.

How do the graphs in these 2 cases compare?

Human Motion

+

0

-

Pos

ition

time Vel

ocity

+

0

-

time

Part 1:

Part 2:

Walk this way & take data

Walk this way,& take data

0feet

10-10

0feet

10

Other class rules (in addition to stuff in syllabus): 1) Turn off cell phones. 2) 1 hour and 15 minute class. (does not end at 12 or 12:05!!)

Human MotionDemo 4: Sketch position vs time and velocity vs time graphs for when moving man - walks steadily towards the tree for 6 seconds- then stands still for 6 seconds, and - then towards the house twice as fast as before. Do yours as dashed line, compare with team members then make solid line based on group.

+

0

-

Pos

ition

time

Vel

ocity +

0

-

time

5 s 10 s 20 s15 s

i don’t remember class very well. seemed like it went reasonably smoothly and was lots of student...

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