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Lecture

# Lecture 1 - Motion, in 2 columns for easy printing+reading, includes diagrams I drew on the computer

Department
Physics
Course Code
PHY131H1
Professor
Jason Harlow

This preview shows half of the first page. to view the full 2 pages of the document. PHY131H1 Summer Lecture #1
Motion
Types:
Translational straight line
Circular circular path, turning
Projectile aka Free-fall following a curved path, the
only force on the object is gravity
The Particle Model
-Restrict attention to objects in motion
-Consider moving object as if a single point
without size or shape, no distinction btwn top +
bottom or front + back
-Treat as if all mass were concentrated into a
single point this object is a particle
Motion Diagrams
Basically overlaying all frames of a movie strip on
top of each other
Of an object at several instants in time
More space btwn dots = moving faster
Faster velocity = longer vector line
Mention Start/Stop if they are there
Vectors = made up 2#s (magnitude +
direction/angle), always straight
ex. Force
C = A+B
Methods: tip-to-tail, parallelogram, components
(using x-y axis, can add on calculator )
Tip-to-tail:
oDraw A
oPlace B tail @ A tip
oDraw arrow from A tail to B t ip
This is vector A + B = C
Vector Subtraction
D = A B = A + (-B)
-B is a vector with the same slope of B, but with
the tail and tip switched
ex. If B = , - B =
Tip-to-tail:
oDraw A
oPlace B tail @ A tip
oDraw arrow from A tail to B tip
This is vector A B = D
Distance (scalar): d, path length [m]
Displacement (vector): r, final position (r
f
) initial
position (r
i
) [m, direction/angle]
d |r|
|x| = magnitude of vector x
Instantaneous velocity aka velocity (very small r):
Vector v = lim
t
0
(r/t) = dr/dt [m/s]
Vector v
avg
= r
1
- r
0
= r [m/s]
t t
Linear Acceleration:
vector a
change in velocity (vector) not speed ( |v|, scalar)
over time
velocity can change in magnitude + directio n
find vector a by drawing v
odo this by drawing v
n+1
v
n
= v
n+1
+ (-v
n
)
odirection of v = direction of a
odraw vector a at the midpoint of v
n
and v
n+1
(
a = avg a at this midpoint)
Vector a = lim
t
0
(v/t) = dv/dt [m/s
2
]
Vector a
avg
= v
1
- v
0
= v [m/s
2
]
t t
Signs
Position (x, y): sign tells where the object is
+r : to the right or above the origin (like
in a co-ordinate axis)
- r : to the lef t or below the origin
Velocity (v
x
, v
y
): sign tells what direction the object is
moving in
+v : moving upwards or to the right
- v : movin g downwards or to the left
Acceleration (a
x
, a
y
): sign tells the direction of the
acceleration vector, does not tell if speeding up or
slowing down
+a : a vector points up or right; can be
when v speeding up, or
when v but slowing down
- a : a vector points down or left; can
be when v but slowing down, or
when v speeding up
Iff (if and only if):
a vector direction = v vector direction: speeding
up
a and v vectors are in opposite directions:
slowing down
a vector = 0: velocity constant
Note: Centripetal acceleration occurs when when
turning at the same speed (changing velocity direction)
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