“Good advice is something a man
gives when he is too old to set a
bad example.”
Francois de La Rochefoucauld
Course web page
http://sdbv.missouristate.edu/mreed/CLASS/PHY12
3
Cell phones put away please.
Announcements
HW1 is on-line now (link on Blackboard)
and today at 5pm. (Problem 16 no
longer being graded)
I set a practice assignment of odd
problems (answers at the back of the
book) on WileyPlus to go with
assignment 1.
Reading: Chapter 2, sections 1-3;
Chapter 3 section 1; and Chapter 4, all.
Math: Trigonometry
Relationships between them.
Vector example
 What is the sum (vector addition)
of the following three vectors?
A = 34 @ 40o
o
A)
R
=
114.6
@
50.4
B = 40 @ 150o B) R = 20.25 @ -49.8o
C = 48 @ 285o C) R = 73.1 @ -3.5o
D) R = 88.4 @ 87.5o
E) Nothing close to the
answers above.
 A = 34 @ 40o
Vector
Ax = 34(cos 40o) = 26.0
A
Ay = 34(sin 40o) = 21.9
B
 B = 40 @
150o
Bx = 40(cos 150o) = 34.6
By = 40(sin 150o) = 20.0
 C = 48 @ 285o
Cx = 48(cos 285o) =
12.4
Cy = 48(sin 285o) = -
X
C
R
First find all the
components.
Y
 A = 34 @ 40o
Vector
X
Y
Ax = 34(cos 40o) = 26.0
A
26.0
21.9
Ay = 34(sin 40o) = 21.9
B
- 34.6
20.0
C
12.4
- 46.4
R
3.8
- 4.5
 B = 40 @
150o
Bx = 40(cos 150o) = 34.6
By = 40(sin 150o) = 20.0
 C = 48 @ 285o
Cx = 48(cos 285o) =
12.4
Cy = 48(sin 285o) = -
Now put the
components back into
a single vector.
 A = 34 @ 40o
Vector
X
Y
Ax = 34(cos 40o) = 26.0
A
26.0
21.9
Ay = 34(sin 40o) = 21.9
B
- 34.6
20.0
C
12.4
- 46.4
R
3.8
- 4.5
 B = 40 @
150o
Bx = 40(cos 150o) = 34.6
By = 40(sin 150o) = 20.0
 C = 48 @ 285o
Cx = 48(cos 285o) =
12.4
Cy = 48(sin 285o) = -
B) R = 5.9 @ -49.8o
 A turtle is traveling east and north
at a velocity of 0.26 m/s at 55o
east of north. How fast is he going
in each direction?
A) 2.1 m/s East, 0.15 m/s North
B) 0.21 m/s East, 1.5 m/s North
C) 0.21 m/s East, 0.15 m/s North
D) 0.41 m/s East, 0.23 m/s North
E) 0.13 m/s East, 0.47 m/s North
N  55o east of north. What
is the other angle?
55o
?
E
This is really the angle we want to use.
35o
 A turtle is traveling east and north
at a velocity of 0.26 m/s at 55o
east of north. How fast is he going
in each direction?
 C) East = (0.26 m/s)(cos 35o) = 0.21 m/s
 North = (0.26 m/s)(sin 35o) = 0.15 m/s
+y
-x
Notes on tan-1
When you use
tan-1 your
answers will
ONLY be between
+90 and -90o.
+x
-y
+y
tan-1 ONLY from
+90 to -90o.
So ONLY
these angles
are covered.
+x
And they only
cover +x
values. What
happens if
you have a -x
value?
-x
-y
+y
-x
-y
tan-1 ONLY from
+90 to -90o.
What
happens if
you have a -x
value?
+x
You have to
add 1800 to it.
(This will give
you angles
larger than
180o, but
that's okay.)
Chapters 2 & 3
Kinematics
 2.1 Displacement
2.2 Speed and Velocity
2.3 Acceleration
2.7 Graphical analysis
3.1 Displacement, Velocity, and
Acceleration in Two Dimensions
Kinematics is defined as the
branch of mechanics that studies
the motion of a body without
regard to the cause of the motion.
(description vs. the reason why)
Dynamics deals with why.
Variables
• Time – determines interval of event.
• Displacement – straight line distance
from start to finish of event.
• Position – place on coordinate system
which may change over time.