Transcript Speed, Velocity, Acceleration

Speed, Velocity, Acceleration
BY: BRIANNA SHIELDS
DO NOW- Get hmwk out!
Complete the physics handout on
front counter
GOAL
 To interpret graphs and solve word
problems involving speed, velocity,
acceleration and momentum
 Motion  Change in position during a
time period
 3 types of motion
– Speed
– Velocity
– Acceleration
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 Speed  1. Definition: Rate at which
an object moves
 2. Formula: Distance divided
by time (d/t)
 3. Units: m/s or km/s
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 Speed  4. Constant speed - speed
that doesn’t change
 5. Average speed- add
speeds, divide by total
number
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 Speed  6. Graphs:
– Time: x-axis
– Distance: y-axis
– Constant speed
– Changing speed
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Copy samples
of these into
your notebook
Cheetah Speed Graph
In one second
how far had the
cheetah run?
In three seconds
how far had the
cheetah run?
What was the
cheetah’s average
speed?
Bicycle Graph
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 After one hour how far had she
traveled?
 Two hours?
 Three hours?
 Four hours?
 Is she traveling at a constant speed?
Why/why not
 During which hours was her speed the
greatest?
 What does the flat line on the graph
Calculating Speed: Example
 If 2 runners ran the same distance
(10km) but one completed it in 3600
seconds and the other in 2800 seconds,
what were each of their average
speeds?
 1: d/t
10km/3600 sec
km/sec
 2: d/t
10 km/ 2800 sec
km/sec
.00278
.00357
Calculating Speed:
Example
 Spirit of Australia, a
hydroplane boat, made
speed records by
traveling 239 miles in
0.75 hours (45
minutes). What is it’s
record breaking speed?
 d/t 239 miles/ 0.75 hr
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 Velocity
 1. Definition: Describes
speed plus direction (n, s, e,
w)
 2. Formula: D/T plus
direction
 3. Units: m/s or km/s, north,
south, east or west
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 Velocity
 4. Velocities can be combined
– Add velocities when in same
direction
– Velocities in opposite direction=
subtract
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 Velocity
 5. Graphs:
– Time: x-axis
– Distance: y-axis
– (same as speed graphs but
also has direction)
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Calculating Velocity:
Example
If a runner is running east at 10 m/s
sec, what is her velocity?
10 m/s east
Calculating Velocity:
Example
 If you’re rowing a boat downstream at
16 km/hr, and the curren is moving at 10
km/hr. How fast does the boat “look”
like it’s going to someone on shore?
(Draw a picture too!)
 16 + 10
 26 km/hr downstream
Calculating Velocity:
Example
If you’re rowing a boat upstream at
15 km/hr, against a current moving
at 8 km/hr. What is you’re actual
velocity to an observer on the
shore?
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15-8
 7 km/hr upstream
Calculating Velocity:
Example
 If you are running up an
escalator at 2 steps per
second and its moving
downward at 3 steps per
second, what is the total
velocity? In what way are
you moving?
 3-2
 -1 (you are actually moving
backwards, down the
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 Accelerati  1. Definition: Rate of change
on
in velocity
– Speeding up, slowing down,
changing direction
 2. Formula: Final velocity
minus original velocity, divided
by time
 3. Units: m/s/s or km/s/s
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 Accelerati  4. Increasing velocity -
on
positive acceleration
 5. Decreasing velocity negative accelerationdeceleration
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 Accelerati  6. Graphs
on
– X- axis- time
– Y-axis- distance
– Object must be
changing
velocity
– Line, is smooth
and curved (not
straight)“changing line”
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Acceleration GraphRace Car
 1. From 0-1 sec how
far did the race car
go?
 2. From 1-2 sec?
 3. From 2-3 sec?
 4. Is the car
accelerating or
decelerating?
Explain.
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Calculating Acceleration:
Example
 A roller coaster’s velocity at the top of a
hill is 10m/s. Two sec later it reaches
the bottom of the hill with a velocity of
26 m/s. What is the acceleration of the
roller coaster?

Vf-Vo
T
26-10
2
8 m/s/s
Calculating Acceleration:
Example
A roller coaster’s velocity at the
bottom of a hill is 25 m/s. Three
seconds later it reaches the top of the
next hill, moving at 10 m/s. What is
the deceleration of the roller coaster?
A =
Vf-Vo
T
A = 10-25 = -7.5 m/s/s
2
Calculating Acceleration:
Example
 A car is traveling at 60 km/hr. It
accelerates to 85 km/hr in 5 seconds.
What is the acceleration of the car?
A=
Vf-Vo
T
A = 85-60 = 5.0 m/s/s
5
 Momentu
m
 1. Definition: Depends on
object’s mass and velocity
– Related to force upon impact
 2. Formula: Mass x velocity
 3. Units: Kg.m/s
Calculating Momentum:
Examples
 If 2 football players are running at the
same velocity towards an opponent.
Player 1 weighed 170 lbs, player 2
weighed 250 lbs. Who is going to move
the opponent farther? Why?
 Since both players were traveling at the
same velocity, the larger player will
have more momentum, thus, moving
the opponent farther
Calculating Momentum:
Examples
 Why would it be harder to
stop a car traveling at 65
miles/ hr than it is to stop
one traveling at 35
miles/hr? Explain
 If they have
approximately the same
mass, the faster car will
gather more momentum,
Calculating Momentum:
Examples
What is the momentum of a 0.3 kg
bluejay running into a window while
flying at 17 m/s?
momentum = mass x velocity
 = 0.3 x 17 = 5.1 kg m/s
Websites
Fear of Physics
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Assignment
Write the homework assignment
into your agenda:
– Practicing Motion