Chapter 2
 What kinds of motion can you describe?
 How do you know that an object has moved? Be
specific.
 Let’s start at the very beginning… Straight Line
Motion.
 A series of images showing the positions of a moving
object at equal time intervals is called a motion
diagram.
 A particle model is a simplified version of a motion
diagram in which the object in motion is replaced by a
series of single points.
 Coordinate Systems
 Tells you the location of the zero point of the variable
you are studying and the direction in which the values of
the variable increase.
 The origin is the point at which both variables have a
value of zero
 Position can be represented by drawing an arrow from
the origin to the point representing the object’s new
location
 The length of the arrow indicates how far the object is from
the origin or the distance.
Vectors
Scalars
 Have magnitude (size) and
 Only have magnitude
direction
 Require the use of
VECTOR ADDITION to
determine resultant
vector
 Can be added or combined
using standard rules of
addition and subtraction
Vector
Scalar
Displacement
Distance
Velocity
Speed
Acceleration
Time
Force
Temperature
 You will need a ruler, protractor, and pencil
 Draw a coordinate system (small) as your origin
 Draw an arrow with the tail at the origin and the head
pointing in the direction of motion.
 The length of the arrow should represent the distance
traveled.
 Add the second vector using the head to tail method.
 Measure resultant magnitude and direction.
 Add vectors using “head to tail” method.
 Pictures do not need to be drawn to scale. No need for
a ruler and protractor.
 Use Pythagorean Theorem and SOHCAHTOA to solve
for resultant vectors ONLY when RIGHT TRIANGLES
are formed. a 2  b 2  c 2
 If not right triangles, use Law of Sines and Law of
Cosines to solve for resultant vectors.
sin A sin B sin C


a
b
c
c  a  b  2abcos
2
2
2
 The difference between two times is called a time
interval and is expressed as t  t f  ti
 i and f can be any two time variables you choose
(according to each problem)
 A change in position is referred to as displacement.
d  d f  di
 Distance ≠ Displacement
 Displacement is the shortest distance from start to finish
or “as the crow flies”
 Draw the following:
 10m East
 -10m
 10m North + 12m West
 Every vector has x- and y- components.
 In other words, a vector pointing southwest has both a
south (y) and west (x) component.
 Vectors can be “resolved into c0mponents”.
 Use SOHCAHTOA to find the x- and y- components
 Break EACH vector into x- and y- components.
 Assign negative and positive values to each component
according to quadrant rules. For instance, south
would have a negative sign.
 Add the x- column. Add the y- column.
 Use Pythagorean Theorem to determine the final
displacement magnitude.
 Use SOHCAHTOA to find the final displacement
direction.
 Plot time on the x-axis and position on the y-axis
 Slope will indicate average velocity
 Use this website for extra help.
http://www.physicsclassroom.com/Class/1DKin/U1L3a.cfm
Shape of Slope
Interpretation
Linear
Constant speed
(can be positive or negative)
Parabolic
Speeding up
Hyperbola
Slowing down
 Average velocity is defined as the change in position,
divided by the time during which the change occurred.
 On a position vs. time graph, both magnitude and
relative direction of displacement are given. A
negative slope indicates an object moving toward the
zero position.
d d f  di
v

t
t f  ti
Speed simply indicates magnitude
or “how fast.”
Velocity indicates BOTH
magnitude and direction. In
other words velocity tells you “how
fast” and “where.”
 When solving for average velocity, two points for
position and time are chosen for comparison.
Individual changes in speed could have taken place
within those intervals.
 Instantaneous velocity represents the speed and
direction of an object at a particular instant.
 On a position-time graph, instantaneous velocity can
be found by determining the slope of a tangent line on
the curve at an given instant.
 So far, we have looked at motion diagrams, particle
models, and graphs as a means of representing
motion.
 Equations are also quite useful.
 Based on the equation y=mx +b, one final equation
will be derived in this chapter.
d  vt  di
d = final position
v = average velocity
t = time interval
di = initial position (based on y-intercept if using a graph)
 Read Chapter 1! You will reinforce all of these
concepts, drill them into your head and see more
examples than I have given here.
 Visit www.physicsclassroom.com This website offers
great explanations of physics concepts.
 Watch this video. It is a little boring but very helpful.
http://www.youtube.com/watch?v=4J-mUek-zGw