Upload
georgiana-campbell
View
233
Download
9
Embed Size (px)
Citation preview
Linear
Motion
Physics
Linear Motion
Linear Motion refers to “motion in a line”. The motion of an object can be described using a number of different quantities.
Time – How long an object is in motion for. In physics, we usually use seconds but in every day life we use minutes, hours, years, etc.
Distance – how far something travels along its path. Can be measured in a wide variety of measurements including kilometers, meters, inches, feet, etc.
Let’s do a Frayer model for
linear motion:
Definition:
How to remember:
Drawing:
Motion in a straight
line
linear motion
vertical horizontal
What it’s NOT:
Speed, velocity, acceleration
Speed - How fast you’re going15 km/hr, 22 cm/s , 2000 mi/hr
Velocity – how fast you’re going in a certain direction
Acceleration - how fast your velocity is changing (speeding up or slowing down)
Example word problem:A soccer ball is moving horizontally at a speed of 3.0
m/s. It then undergoes a constant negative acceleration. After 4.0 s, the ball is moving at 1.5 m/s.
●Instantaneous Speed is the speed at any
specific instance or moment in timeoEx. On a speedometer reading…
you are traveling 35 mph (mi/hr)
or 50 km/h or 25 m/s
●Average Speed is the total distance covered
divided by total time
Types of Speed
How do you calculate average
speed?●The average speed of an object is defined as the total
distance traveled divided by the total time elapsed
Average Speed = total distance total time
Speed = d t Michael Phelps can swim a 200 m
butterfly race in 1:52.09. What would be his average speed?
Speed, cont
Speed is a scalar quantity, meaning it has no
direction. Other examples include distance and time.
Example:
speed: I was going 75 mi/hr
mass: I weigh 75 kilograms
time: there are 45 minutes left of class
Vector
Some quantities are vectors, meaning a number with a unit and direction
Common vectors that we deal with in physics include
displacement, velocity, and acceleration.
Pictorial Representation
●An arrow represents a vector
oLength = magnitude (size) of vector
oDirection = direction of vector
Pictorial Representation
●This arrow could represent a vector of
magnitude 10 point to the “right”
●This arrow could represent a vector of
magnitude 5 point to the “left”
Practice!
●Draw an empty Venn Diagram like this
Scalar Vector
Label one side scalar, other
vector
●Magnitude
●Size
●Direction
●Units
●Distance
●Displacement
●Speed
●velocity
●Acceleration
●Mass
●Weight
●12 cm
●47 kg (mass)
●470 Newtons (weight)
●50 meters
●50 meters West
●25 m/s
●25 m/s toward home
●25 m/s away from home
●10 m/s2
●10 m/s2 toward the ground
Place these words in the correct space on the diagram:
Displacement vs. distance:
1. Displacement: how far its position is from the starting point
(in meters with a direction). A measurement of how far you
“displaced” meaning changed your position. Remember,
displacement is a vector so you need a direction!
Example:
I can jump 4 feet, up.
oDistance: how far an object travels (in meters)
Displacement Isn’t Distance
●The displacement of an object is not the same
as the distance it travelsoExample: Throw a ball straight up and then catch
it at the same point you released it The distance is twice the height
The displacement is zero
Distance & Displacement
Distance & Displacement
B
A
C
5 m
4 m
3 m
Your distance traveled is 7m
You walk from A to B to C.
What is your distance traveled?
What is your displacement from A?
Your displacement form A is 5 m
Horizontal Displacement
• When displacement is horizontally oriented, we refer to an “imaginary line”.
• Any displacement to the right (or forward) of the line, we have a positive displacement.
• Any displacement to the left (backwards) of the line, we experience a negative displacement.
Vertical Displacement• Just as we do with horizontal displacement, we refer to an
imaginary y-axis.
• Moving up the line will be a positive displacement, and moving down the line will be a negative displacement.
Let’s do Frayers for distance &
displacement:
Definition:
Don’t confuse this with:How to remember:
Drawing:
Velocity
●The average velocity of an object is defined
as the total displacement traveled divided by
the total time elapsed
●Velocity is a vector quantity
Average Velocity = total displacement total time
V = x t
Velocity
●It takes time for an object to undergo a displacement
●The average velocity is rate at which the displacement occurs
●generally use a time interval, so let ti = 0
V (average) = Δx = Xfinal – Xinitiative = xf - xi Δt tfinal –tinitiative t
Velocity, cont.
●Pull back car example and demonstration
Speed vs. Velocity
●Cars on both paths have the same average velocity
since they had the same displacement in the same time
interval
●The car on the blue path will have a greater average
speed since the distance it traveled is larger
Let’s do Frayers for speed &
velocity
Definition:
Don’t confuse this with:How to remember:
How to calculate:
Speed vs. Velocity
●You drive from Yakima to Seattle (140 miles away)
●You stop in Ellensburg for a 2 hr lunch with a friend.
●Your total driving time is 2 hours
●What is the average speed?
●What is the average velocity?
●Remember,
speed = total distance/ total time
Concept Map: Linear Motion
The position
changing
How quickly the
position changes
called
called
which is
calculated by
which is
calculated by
which is
calculated by
which is
calculated by
Adding all legs
of the journey
distance
displacemen
t
speed
velocit
y
Xfinal –x initial
Total distance
Total time
xfinal –x initial
time
Acceleration●Acceleration is a measure of how quickly
velocity is changing.
●Change in velocity divided by the change in time
TIME 0.00 sec 1.00 sec 2.00 sec 3.00 sec 4.00 sec
VELOCITY 0 mi/hr 10 mi/hr 20 mi/hr 30 mi/hi 40 mi/hr
Acceleration
Great animation showing acceleration:http://www.physicsclassroom.com/mmedia/kinema/acceln.cfm ●Changing velocity (not constant) means an
acceleration is present
●Units: m/s2 (SI) other examples: cm/s2 ft/s2
Relationship Between Velocity &
Acceleration
●Uniform velocity (shown by red arrows maintaining
the same size)
●Acceleration equals zero
Relationship Between Velocity &
Acceleration
●Velocity and acceleration are in the same direction
●Acceleration is uniform (blue arrows maintain the
same length)
●Velocity is increasing (red arrows are getting longer)
●Positive velocity and positive acceleration
Relationship Between Velocity &
Acceleration
●Acceleration and velocity are in opposite directions
●Acceleration is uniform (blue arrows maintain the
same length)
●Velocity is decreasing (red arrows are getting shorter)
●Velocity is positive and acceleration is negative
Acceleration
Sometimes we are given acceleration and want to know the velocity of an object after a certain amount of time passes. We can figure the velocity out by simply rearranging the equation:
To look more like:
Velocityfinal = Velocityinitial + at
Let’s do a Frayer for acceleration :
Definition:
Don’t confuse this with:How to remember:
How to calculate:
Acceleration Example 1
A bird is flying at a speed of 35.8 m/s. If it
takes 2.0 s to come to a complete stop,
what acceleration would it have?
Example 2
I can run at a speed of 25 m/s and accelerate at 3.0 m/s/s for 5 seconds. How fast would I be running after 5 seconds?
Acceleration Example 3
●A car is said to go "zero to sixty in six
point seven seconds". What is its
acceleration in m/s2?
Acceleration example 4
A toy traveling at 50 cm/s and slows down to 20 cm/s in 10 seconds. What is the toy’s acceleration?
Concept Map: Linear Motion
The position
changing
How quickly the
position changes
The rate at which the
movement changes
called
called
which is
calculated by
which is
calculated by
which is
calculated by
which is
calculated by
which is
calculated by
Adding all legs
of the journeydistance
displacemen
t
speed
velocit
y
acceleratio
n
Xfinal –x initial
Total distance
Total time
xfinal –x initial
time
vfinal –v initial
time
called