Physics Bell Work, Sept 28 – Oct
2, 2015
Physics: Instantaneous Velocity, Average
Velocity, Constant Acceleration, Motion Maps of
Uniform Acceleration
Physics Bell Work, Monday, Sept 28
1. What is a time interval?
It is the difference between two clock readings,
where ∆ 𝒕 = 𝒕𝒇 - 𝐭 𝒊
ti
tf
2. What is an instant in time?
It is one clock reading at a single time.
Thus, the final time and the initial time are the same and ∆ 𝒕 = 0
3. What is instantaneous velocity?
It is an object's speed at a given time instant (or a single clock
reading).
4. What is the difference between average velocity and
instantaneous velocity?
Average velocity is the average velocity over a time interval (2 more
clock readings), instantaneous velocity is the velocity at one clock
reading (a single instant in time).
Physics Bell Work Tuesday, Sept 29, (2 Ques.)
1. What is instantaneous velocity?
The speed and direction of an object at a particular point in time is
called the instantaneous velocity
2. a. Describe, using a clear, complete sentence, how does the
motion (not the graph shape) of object 2 differs from the motion
of object 1 on the position – time graph below.
b. Sketch the graph of velocity vs time for object 1 and object 2. (label clearly)
a. Both objects
travel in the
same direction
at the same
speed, but
object 2 has a
head start.
Object 1
Object 2
Physics Bell Work, Wednesday, Sept 30
1. Draw a motion map for the jogger shown above.
Assume the jogger covers 5 m every second
5
10
15
20
25
meters
Physics Bell Work, Wednesday, Sept 30
Δt = 1s
2. Draw a motion map for the runner shown above showing
that velocity is not constant but acceleration is uniform .
v
a
v
a
v
a
v
a
a
v
v
v
a
a
Physics Bell Work, Wednesday, Sept 30
3. How are motion maps in questions 1 & 2 different?
Map 1 is constant velocity (arrows same length, same dot spacing.
Map 2 is increasing velocity (each arrow longer, dot spacing bigger).
Physics Bell Work, Thursday, Oct 1 (5 ques.)
Sketch the
graph.
time (s)
1. What does this graph tell you about velocity?
The velocity is increasing at a constant rate with time ( one slope).
2. Calculate
the slope
𝒎 of this v-t graph.
𝒎
(𝟐𝟎−𝟎)
𝒔
𝒔
𝒎
= 10 𝒔
(𝟐−𝟎) 𝒔
𝐦
𝒎
𝟏
𝒎
𝒔
= 𝒔 =
•
=
𝐬
3. What are the units of this slope?
𝒔
𝒔
𝒔𝟐
𝐬
Meters per second per each second
𝟏
Physics Bell Work, Thursday, Oct 1 (5 ques.)
4. What is the significance of the slope of this v-t graph?
∆𝒗
The slope, m, =
= a , acceleration
∆𝒕
Because the slope is constant (a straight line), the acceleration is
constant or uniform.
5. If the time interval is 1 s (Δt = 1 s) what does acceleration tell
you?
How fast the velocity is changing (increasing or decreasing) each
second.
Physics Bell Work, Thursday, Oct 1
6. Draw a line that from
2s – 4s.
7. Calculate the slope of this
line.
8. What is this line?
The average velocity from
2s – 4s.
9. Draw a tangent at 3 s.
Compare and contrast what these
slopes mean for the two lines.
Both slopes are the same. The
slope of the tangent line tells us
that the instantaneous velocity
at the 3s clock reading is
30.0cm/s.
(4, 80)
(4, 75)
(2, 20)
(2, 15)
#9: The slope of a position vs. time
graph is the average velocity if the
slope is over a time interval. If it is
the slope at a point it is the
instantaneous velocity.
IB Physics Bell Work, Tuesday, Mar 3 (3 ques)
1. Draw a line tangent to the
graph at t = 3.0 s.
2. Calculate the slope of this
tangent line. Compare
average & instantaneous
velocity.
(4, 80)
(4, 75)
(2, 20)
3. Explain what the slope of
tangent line tells you about
the motion of the object.
This slope of the tangent line
tells us that the instantaneous
velocity at the 3s clock reading is
30.0cm/s.
(2, 15)
#2: The slope of a position vs. time
graph is the average velocity if the
slope is over a time interval. If it is
the slope at a point it is the
instantaneous velocity.
Physics Bell Work, Thursday, Mar 5, 2015
vo = 0 cm/s
x = 0 cm
Draw the diagram
x = 50cm
x = 25 cm
2. Draw a motion map along the ramp for the motion of
the ball when released from rest.
3. Draw an x-t, v-t & & a – t (acceleration – time) graphs
that shows
this motion
a
v
a
v
a
v
x = 0 cm
a
a
a
v
x = 25 cm
v
v
x = 50cm
Physics Bell Work, Thursday, Mar 5, 2015
(s)
(s)
Acceleration m/s/s
(cm/s)
3. Draw the graphs
+
0
Time (s)
-
Physics Bell aWork
Thursday,
Mar
5,
2015
a
a
a
vo = 0 cm/s
a
a
v
x = 0 cm
a
a
v
v
v
v
v
v
x = 25 cm
Draw the
diagram
x = 50cm
4. Draw a motion map along the ramp for the motion of
the ball when released from rest.
5. Draw an x-t, v-t, & acceleration time (a-t) graphs that
shows this motion
Physics Bell Work Thursday, Mar 5, 2015
Physics Bell Work Thursday, Mar 5, 2015
Physics, Bell Work, Monday, Feb 23, 2015
1. How is the ACT science test constructed?(left side, #1; right side #2)
40-questions, 35-minutes, scored: 0 – 36. You need 21/40 for TOPS.
There are three types of passages, followed by questions.
Data Representation questions (graphs/data tables) : 38% of the test.
Research Summaries questions (intrepret experiments or summary of
results) : 45% of the test.
Conflicting Viewpoints (reading 2 different hypothesis):17% of the test.
2. How can you identify each of the three types of passages?
Data Representation passages are always followed by 5 questions.
Research Summaries passages are followed by 6 questions.
Conflicting Viewpoints are followed by 7 questions.
There are always: 3 Data Representation passages
3 Research Summaries passages
1 Conflicting Viewpoints passage
Physics Bell Work Tuesday, Feb 24, (2 questions)
1. Explain how to take the ACT.
• Write in the test booklet. Circle your answers in the booklet.
• Start by answering the questions that go with the type
passages you are best at (either Data Representation,
Research Summary, of Conflicting point of view.)
• Then answer those questions in your next best category, and if
time permits, answer your worst category questions last.
• When the teacher says five minute left, bubble in your answer
document, and start guessing for all answered questions.
• Do not leave any questions unanswered.
• Guess!!!
Physics Bell Work Tuesday, Feb 24,
2. Explain an ACT guessing strategy
• The answer sheet looks like this:
Position: 1
2
3
4
A
B
C
D
F
G
H
J
• If you have no idea which is the correct answer or you are out of
time, choose one of these “positions” (like B & G, or D & J) and
always use those letter pairs for your guess answers.
• If you can use process of elimination to “cross out” one of the
four answers, you are not guessing.
• In this case, go with your best hunch, or use the first answer
that you did not eliminate.
• Example: You know F & J are wrong but unsure about G & H
F
G
H
J Your answer is G because it is
the first answer not crossed off.
Physics Bell Work, Wednesday, Feb 25
1. What is a time interval?
It is the difference between two clock readings,
where ∆ 𝒕 = 𝒕𝒇 - 𝐭 𝒊
ti
tf
2. What is an instant in time?
It is one clock reading at a single time.
Thus, the final time and the initial time are the same and ∆ 𝒕 = 0
3. What is instantaneous velocity?
It is an object's speed at a given time instant (or a single clock
reading).
4. What is the difference between average velocity and
instantaneous velocity?
Average velocity is the average velocity over a time interval (2 more
clock readings), instantaneous velocity is the velocity at one clock
reading (a single instant in time).
Physics Bell Work, Thursday, Feb 26, ’15 (4 Ques.)
1. The change in an object’s position calculated by subtracting
the initial position from the final position, ∆ 𝒙 = 𝒙𝒇 - 𝒙𝒊 , is
a.
acceleration
c.
displacement
b.
average velocity
d.
scalar magnitude
velocity (m/s)
displacement ∆𝒙.
2. State two other ways to determine ____________,
By using the equation: ∆ 𝒙 = 𝒗 • 𝒕 (𝒐𝒓 𝒗 • ∆𝒕 )
By finding the area under a v vs. t graph. (The area between the
Draw the graph
4
0
-2
red & blue lines.)
3. Describe the motion shown on this
graph.
From 0 – 3 s (or for 3 s), the object
3
7
t (s) moves at 4m/s and then reverses
direction from 3 to 7 seconds (or
for 4 seconds) and moves at -2 m/s.
Physics Bell Work Thursday, Feb 26, (1 Ques.)
v • Δt = Δx
𝒎
𝟒
𝟑𝒔 − 𝟎𝒔 = 𝟏𝟐𝒎
𝒔
Area under line = Δx = 4• 3 = 12 m
velocity (m/s)
Draw the graph
4
0
-2
3
7
t (s)
v • Δt = Δx
𝒎
−𝟐
𝟕𝒔 − 𝟑𝒔 = −𝟖𝒎
𝒔
Area under line = Δx = -2• 4 = -8 m
1. What is the displacement (Δx) from 0 – 7 seconds?
From 0 s - 3 s, Δx = 12 m.
From 3 s - 7 s, Δx = -8 m.
From 0 s - 7 s, Δx = 12 m + (-8 m) = 4 m
Physics Bell Work Thursday, Feb 26, (1 Ques.)
Draw the diagram
vo = 0 cm/s
x = 0 cm
x = 25 cm
x = 50cm
5. Draw a motion map along the ramp for the motion of
the ball when released from rest.
6. Draw an x-t & v-t graph that shows this motion
x = 0 cm
x = 25 cm
x = 50cm
Physics Bell Work Thursday, Feb 26, 2015
(cm/s)
6. Draw the graphs.
(s)
(s)
Physics Bell Work Wednesday, Feb 25, (1 Ques.)
1. What are the “four steps “ used as you read and
answer ACT science reasoning passages?
Step 1. Skim and identify the passage. Do not read the
passage carefully at first!
You should be able to complete this step in less than a minute.
Skim to find what each paragraph is all about.
Only read the first and last sentences.
Look over any charts and diagrams just enough to get
an idea of what they are about.
Don't try to read or interpret the data just yet. You just want to
know what sort of data is available.
Look carefully at any words in italics or bold
print.
Physics Bell Work, Wednesday, Feb 25, (1 Ques.)
Step 2. Read the question and all the answers. Read
each question and all the answer choices.
Be sure you are clear about what the question is asking. You want
to answer the question on the test, not some other question.
Step 3. Eliminate obviously incorrect answers. Cross off
any answers you're sure are incorrect in test book.
Eliminating incorrect answers is a big help in determining the
correct answer.
Step 4. Choose the correct answer from the remaining
choices.
Choose the answer that is most correct.
If you don't know the correct answer, guess.
Never leave an answer choice blank.
Physics Bell Work, Monday, Feb 9
2. Which object started further
from the origin, A or B? How
∆𝒙
do you know
v=
= slope
∆𝒕
B, its further from the origin
along the position axis.
3. Which object has the greater
final position? How do you
know?
A, its further from the origin
along the position axis.
4. Which object is going faster?
How do you know?
A, it covered more ground in the
0
same amount of time. Also, the
1. What does the slope of a line slope of A is greater than B.
on a position – time graph The slope of a position-time graph gives
mean? you the average velocity over that time interval.
Sketch the graph.
Results of ACT I Test
A
Type of Passage
B
Passage
Numbers
(question
numbers)
Data Representation
( 5 questions follow
the passage)
1,2, 6
Research Summary
(6 questions follow
the passage)
3, 4, 7
F
C
Number of
correct
answers not
Total number including
of questions guesses
Percent
Correct
Answers
( F/C) * 100
15
6
75%
18
9
100%
7
7
0%
(questions 110, 30 – 34)
(questions
11-22, 35 –
40)
Conflicting Viewpoints 5 (questions
(7 questions follow the 23 - 29
passage)
WS-1, Motion Maps and Position vs. Time Graphs,1
1
Red
Problem 1
2
Blue
Problem 2
3
Pink
Problem 3, a & b
4
Orange
Problem 3 c & d
5
Green
Problem 3 e & f
1
White
Problem 1
2
Yellow
Problem 2
3
Brown
Problem 3, a & b
4
Grey
Problem 3 c & d
5
Purple
Problem 3 e & f
Unit 2 Worksheet 1
# 4.
Unit 2 Worksheet 1, # 4
a. How does the motion of the cyclist A in this graph compare to
that of A in question 3?
A starts well to the right of the origin, is moving at about the same speed,
but in the opposite direction as it was in the previous question.
b. How does the motion of cyclist B in this graph compare to that
of B in question 3?
The motion of B is the same as it was in the previous question.
c. Which cyclist has the greater speed? How do you know?
A is moving faster because the absolute value of its slope is greater
than that of B.
d. Describe what is happening at the intersection of lines A and B.
A and B are at the same place at the same time; they are passing
one another.
e. Which cyclist has traveled further during the first 5 seconds?
How do you know? A has traveled a greater distance because its
|x| is greater than that of B.
Unit 2 Worksheet 1, # 4
f. Draw motion diagrams for these graphs.