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Physics I Honors
Good morning
• You measure your new yard with a meter stick so that the dimensions are 20m±3cm by 30 meters±6cm. How do you make sure you will not be short ordering the perimeter fencing and the square meters of sod?
Physics I Honors
Good morning part II
• You live on a square block 500m each side. You jog 3 times around the block. What distance did you run? What was your displacement?
• You travel 30m east then 40m south. What was your displacement?
Physics I Honors
Kinematics I - Velocity
Position and Distance
Physics I Honors
Kinematics• Is the study of motion without regard for the
forces causing the motion or …• the description of motion using:
Position (s)– The location of an object in space
– changes in position can be described by distance or displacement
Velocity (v)– how fast an object is changing its position
Acceleration (a)– how fast the velocity of an object is changing
Physics I Honors
Position vs Distance
• Position – Must be defined relative to a reference point.
– Must be defined using both magnitude and direction.
– Position (s) is the location of an object in space
– units: m, cm, km
• Distance– Distance is the separation between any two points.
– It is a scalar quantity, defined only by magnitude.
Physics I Honors
What is a Scalar?
• A scalar is a quantity that is described only by magnitude…such as distance. – it may have units e.g. kg (it may not)– it does not have any direction
– it may have a sign +ve or -ve
– it may be real, or integer
– The distance from Jacksonville to Baldwin is 10 kilometers.
Physics I Honors
Displacement
• A objects displacement is defined as the separation between an object and a reference point.
• It is a vector quantity, defined by magnitude and direction.
• Displacement is the change in position of an object (d = sf - si)
si
sf
d = sf – si
displacement = dd
Physics I Honors
What Is a Vector?
• A vector is a quantity that must be described by magnitude and direction.
• Magnitude– Size or quantity in unit of measurement– 10 meters, 5 Newtons
• Direction– Compass direction: North, Southeast– Angle: 25o from the positive x axis
Physics I Honors
Vector– an arrow drawn to scale used to represent a
vector quantity
F–vector notation
Physics I Honors
End of day 3
Physics I Honors
Graphical (Tip-to-Tail ) Method
• Example 1: Add these vectors using the tip-to-tail method.
A B+
Physics I Honors
Graphical (Tip-to-Tail) Method
C
A
B
A B C+ =
CIs the resultant
Physics I Honors
What is a Resultant?
Physics I Honors
How does one solve for displacement?d = sf – si
d = (x1,y1) – (x2,y2) How do you do this?
• Realize that displacement is a vector so you must decide to use either the Cartesian or polar coordinates
d
si = (xi,yi)
sf = (xf,yf)
d = sf– si
X
Y
Physics I Honors
Describing Vectors
• Cartesian Coordinates (dx,dy)
• dx = x2 – x1 = distance in the x-direction
• dy = y2 – y1 = distance in the y-direction
• Polar Coordinates (d,)
• “How far and in which direction”2
122
12 )()( yyxxd
= measured directly from graph
Physics I Honors
Describing Distance
leg 1 = 2 miles
leg 3 = 2 miles
leg 2 = 3 miles
N
Total DISTANCE Traveled= 2 miles + 3 miles + 2 miles
= 7 miles
Physics I Honors
Describing Displacement
N
disp
lace
men
t vec
tor
Describing Displacement
First Method (Cartesian)3 miles East4 miles North(3, 4) miles
put ‘horizontal’ coordinate 1st
put ‘vertical’ coordinate 2nd
Physics I Honors
Displacement Magnitude
N
disp
lace
men
t vec
tor
3 miles
4 m
iles
Second Method (Polar)1st - calculate length ofdisplacement vector
Physics I Honors
Displacement Direction
N
disp
lace
men
t vec
tor
3 miles
4 m
iles
2nd – Calculate the angle using trigonometric relationships
hordverd1tan
1.5334tan 1milesmiles
Physics I Honors
Displacement Vector(Polar Notation)
Describe the displacement vector by its length and direction
1.53,5milesd
N
disp
lace
men
t vec
tor
3 miles
4 m
iles
Physics I Honors
Kinematics I - Velocity
Graphing
Physics I Honors
Objectives for Graphing
• Measure, graph, analyze, and interpret laboratory data.
• Identify the relationships that may exist between variables (direct, inverse, and quadratic) and the graph shapes, which indicate these relationships (straight line, hyperbola, and parabola).
Physics I Honors
GRAPHING
• Graphing is the pictorial relationship between quantities
– coordinate = any point w/in a graph.– Slope = rise / run or y / x
= means change
x = horizontal axis
y = vertical axis
Physics I Honors
All relationships involve only two variables.All relationships involve only two variables.
• The Independent Variable – – this is the variable that you control or manipulate.
– It is almost always plotted on the X-axis.
• The Dependent Variable – – this is the variable that responds to the independent
variable.
– It is usually plotted in the Y-axis.
Physics I Honors
Graphical Analysis
• Graphical analysis provides a tangible representation of a relationship from which you can make predictions and inferences.– Mass of a substance vs. volume– Speed of a car vs. braking distance– Amount of light vs. plant growth
Physics I Honors
What are the rules?
• The graph has a title…• The scale of the graph is determined by the range
of the data and does not need to start at 0,0• The independent variable is plotted on the x-axis• The dependent variable is plotted on the y-axis• All variables have names and units• You construct a best fit line through the points
Physics I Honors
Linear RelationshipsLinear Relationships
• The dependent variable varies directly with the independent variable.
• Plot is a straight line.• y x or y = kx• y = mx + b
Physics I Honors
Parabolic (Exponential) RelationshipParabolic (Exponential) Relationship
• The dependent variable varies with the square of the independent variable.
• y x2 or y = kx2
• Plot does not appear as a straight line.
• Note that one variable changes faster than the other resulting in a curved line.
Physics I Honors
Inverse (Hyperbolic) RelationshipsInverse (Hyperbolic) Relationships
• The dependent variable varies in the opposite direction of the independent variable.
• As x goes up, y goes down.
• y 1/x or y = k/x
• This results in a line that starts high and ends low. It can be straight or curved.
Physics I Honors
Graphical AnalysisGraphical Analysis
S lop e A rea U n d er th e C u rve
G rap h ica l In fo rm ation
In te rp o la tion E xtrap o la tion
P red ic tion an d In fe ren ce
G rap h ica l A n a lys is
Physics I Honors
SlopeSlope expresses the relationship between expresses the relationship between the variables.the variables.
• How y is changing as x is manipulated.
• M = Y/X
• Y = Y2-Y1
• X = X2-X1
• The units of the slope define the meaning of the slope.
Physics I Honors
Area Under the Curve
• The shaded area is the area under the curve.
• You determine the area by adding up the areas of each triangle and square.
• Again, the units of this calculation, define what the number represents.
Physics I Honors
Interpolation and ExtrapolationInterpolation and Extrapolation
• Interpolation is the reading or analysis (inference or prediction) of the graph from within the plotted data points.
• Extrapolation is the reading or analysis (inference or prediction) of the graph from outside of the plotted data points. This can lead to a significant source of error.
Physics I Honors
Kinematics I - Velocity
Position-Time Graphs
Physics I Honors
Graphing the Relationships Between s, v, & a
• s is the position
• v is the rate of change of s with time
• a is the rate of change of v with time
• consider a graph of s vs. time– s on vertical axis– time on horizontal axis– rate of change is interpreted as the slope
Physics I Honors
Good morning III
• What is the position time characteristic for uniform motion, i.e. constant velocity
• What will it plot as?
• What is the slope???
Physics I Honors
Position – Time for Constant Velocity
Physics I Honors
Position – Time for Constant Velocity
Physics I Honors
Position – Time for Acceleration
Physics I Honors
Slope of Position-Time is Velocity
Physics I Honors
Changes in the slope
• quick change– very steep slope
•positive slope–up and to the right
•negative slope–down and to the right
•slow change–very flat slope
Physics I Honors
Slope Practice 1
• Calculate the velocity of the object whose graph is shown above.
• -24m/8s = -3 m/s
Physics I Honors
Slope Practice 2
• Determine the velocity of the object whose motion is graphed at the left.
• 20m/5s= 4 m/s
Physics I Honors
example
• Text page 52, #46,47
Physics I Honors
Kinematics I - Velocity
Speed
Vs
Velocity
Physics I Honors
Speed
• A scalar quantity referring to how fast an object is moving. – A fast-moving object has a high speed while a
slow-moving object has a low speed. – An object with no movement at all has a zero
speed.
• The distance traveled per unit time.
• It units are meters per second (m/s).
t
dv
Physics I Honors
Velocity
• Velocity is a vector quantity describing displacement per unit time.
• Its units are meters per second (m/s).
• It is defined relative to a reference point.
• Velocity describes both speed and direction.• Depending on your direction, it can be
negative or positive.
Physics I Honors
Average Speed
• Total distance divided by total time of travel; • Rate you would have to travel constantly to cover
the same distance in the same time
t
dvav
Physics I Honors
Average Velocity• Total displacement divided by total time of travel;• Rate you would have to travel constantly to cover
the same displacement in the same time
if
if
tt
dd
t
dv
Physics I Honors
Kinematics I - Velocity
Instantaneous Velocity
Physics I Honors
Average and Instantaneous
• instantaneous speed – speed at any given instant in time; speedometer reading, for example
• instantaneous velocity - specifies how fast and in what direction one is moving at one particular point in time
• magnitude of instantaneous velocity is exactly the same as instantaneous speed
Physics I Honors
From a Graph
• Instantaneous Velocity– the slope of the displacement versus time graph– Determine the average velocity– Take average between smaller and smaller intervals– Until you get to the tangent line– The slope of the tangent line is the instantaneous velocity at that point in time
Physics I Honors
Kinematics I - Velocity
Problem Solution
Physics I Honors
Problem Solution Guidelines• Draw a sketch
– Indicate origin and positive direction
• List the given quantities using the symbols of the equations. (di, vi, a)
• Identify the unknown• Write the general equation of kinematics you will
be using, i.e.2
21 attvdd
iiatvv if
Physics I Honors
More Guidelines
• Isolate the unknown.• Rewrite the isolated equation using the known
quantities.• Check your units• Make sure you are answering the question asked.
– Your answer may be perfectly correct for the wrong question.
Physics I Honors
Kinematics I - Velocity
Velocity-Time Graphs
Physics I Honors
Velocity – Time for Constant Velocity
Physics I Honors
Velocity – Time for Constant Acceleration
Time (s)
Velocity(m/s)
0 0
1 10
2 20
3 30
4 40
5 50
Physics I Honors
Velocity – Time for Zero Acceleration
Time (s)
Velocity(m/s)
0 10
1 10
2 10
3 10
4 10
5 10
Physics I Honors
Area Under Velocity-Time Graph
• The shaded area is representative of the distance traveled by the object during the time interval from 0 seconds to 6 seconds.
Physics I Honors
Area Under Velocity-Time Graph
• The shaded area is representative of the distance traveled by the object during the time interval from 0 seconds to 4 seconds.
Physics I Honors
Area Under Velocity-Time Graph
• The shaded area is representative of the distance traveled by the object during the time interval from 2 seconds to 5 seconds.
Physics I Honors
Constant Positive Velocity
Physics I Honors
Constant Negative Velocity
Physics I Honors
Positive Velocity Positive Acceleration
Physics I Honors
Positive Velocity Negative Acceleration
Physics I Honors
Negative Velocity Negative Acceleration
Physics I Honors
Negative Velocity Positive Acceleration
Physics I Honors
Speeding Up & Slowing Down
Negative acceleration can mean speeding up or slowing down. The same is true with positive acceleration.
Physics I Honors
Passing Lane – Position-Time
Physics I Honors
Passing Lane – Velocity-Time
Physics I Honors
Vector Addition in One Dimension
Physics I Honors
homework
• Motion hand out
• Text page 55 do multiple choice practice test
• Visit physicspp.com