Transcript Slide 1

Physics 31
Friday August 29
Our Class
Major 17 Bio, 1 Eng, 1 Psychology
HS Physics 11/19 yes
Calculus I or higher, taken or taking 14/19
22 Lab 14 yes
MCAT or PCAT 5 yes
EXCEL 16 yes
What is the difference between speed and velocity?
1. Speed is an average quantity, while velocity is not.
2. Velocity contains information about the direction of motion
while speed does not.
3. Speed is measured in mph, while velocity is measured in
m/s.
4. The concept of speed applies only to objects that are
neither speeding up nor slowing down, while velocity
applies to every kind of motion.
5. Speed is used to measure how fast an object is moving in
a straight line, while velocity is used for objects moving
along curved paths.
The quantity 2.67 x 103 m/s has
how many significant figures?
1
2
3
4
5
4
5
6
7
8
9
10
21
22
23
24
25
26
27
28
29
30
11
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13
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16
0%
17
18
0%
19
20
5
3
0%
4
2
1
1
0%
3
0%
2
1.
2.
3.
4.
5.
If Sam walks 100 m to the right,
then 200 m to the left, his net
displacement vector points
3
4
5
6
7
8
9
10
21
22
23
24
25
26
27
28
29
30
11
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15
ou
tf
ur
ze
ro
16
0%
t. .
.
ng
th
le
th
e
To
te
ll w
ith
Ha
s
14
no
t
2
0%
le
ht
rig
th
e
1
0%
ft
0%
17
Ca
n
To the right
To the left
Has zero length
Cannot tell without
further information
To
1.
2.
3.
4.
18
19
20
Vectors and Motion
A quantity that requires both a magnitude (or size) and a direction can be
represented by a vector. Graphically, we represent a vector by an arrow.
The velocity of this car is 100 m/s (magnitude) to the left (direction).
This boy pushes on his friend with a force of 25 N to the right.
Slide 1-28
Displacement Vectors
A displacement vector starts at an
object’s initial position and ends at its
final position. It doesn’t matter what
the object did in between these two
positions.
In motion diagrams, the
displacement vectors span
successive particle positions.
Slide 1-29
QUIZ #1
• Alice is sliding along a smooth, icy road on
her sled when she suddenly runs headfirst
into a large, very soft snow bank that
gradually brings her to a halt. Draw a
motion diagram for Alice. Show and label
all displacement vectors.
• Make a plot of her velocity vs. time. Plot
same times as in part 1.
• Name on paper
Adding Displacement Vectors
Slide 1-31
Example: Adding Displacement
Vectors
• Jenny runs 1 mi to the northeast, then 1 mi
south. Graphically find her net
displacement.
N
E
W
S
Adding Vectors Graphically
Slide 1-33
Velocity Vectors
Slide 1-34
Example: Velocity Vectors
Jake throws a ball at a 60° angle, measured from the horizontal. The ball is
caught by Jim. Draw a motion diagram of the ball with velocity vectors.
Slide 1-35
Adding velocity vectors
•
add red vector to initial
velocity to get next velocity
vector and so on…..
Homework for today
• Problems Ch. 1: MC24, MC28, 9, 10,
25, 36, 37, 38, WB 1.6(27,28)
Homework for Monday
• NO ClassLABOR DAY
Homework for Wednesday
• Reading: 2: 1-2-Motion in One DimensionConstant Velocity
• Problems: 1: 28, 30, 32, 35, 43, 47, 51, 56