Chapter 11
Motion
You will need a
calculator for
this chapter!
Section 11.1
Distance and
Displacement
p. 328
What is a frame of reference?
 How fast was the boat traveling?
 Relative to what?
 Motion must be described relative to a
frame of reference
 relative motion
 Relative to Earth’s surface (understood)
How fast was the boat
traveling?
 Relative to spectators?
 Really Fast!!!!
 Relative to driver?
 ZERO!
 Driver & boat…same frame of reference
 Tennis ball ex…(p.329)
Einstein’s Theory of Relativity – 10:06
Choosing a Frame of
Reference
Conclusion??
The Frame of Reference
determines how motion of
an object is described.
Measuring Distance
 Distance - length btwn 2 pts
 SI unit….meter (m)
 Derived units
 cm (snail crawling)
 km (distance btwn 2 cities)
Measuring Displacements
 distance v.s. displacement?
 “walk 5 blocks” (distance )
 “walk 5 blocks north from the bus stop”
(displacement) – direction & distance
from start to end
 Displacement needed for accurate directions
Combining Displacements
 Vector?
 Measurement w/ magnitude and direction
 Magnitude? Size, length, amount
 Described w/
Displacement along a
straight line
 2 vectors… same direction
 Add magnitudes
 Ex. A car travels 10 km north, stops to
refuel, then travels 20 km north
 total distance = 30 km
 total displacement = 30 km
 (10 km north + 20 km north) from starting pt
Displacement along a
straight line
 2 vectors…. opposite directions
 Subtract mags
 Ex. Bicyclist travels 5 km east, turns
around and travels 3 km west
 Bicyclists total distance = 8 km
 total displacement = 2 km east
 (5 km – 3 km)
Displacement That isn’t
along a straight path
 2+ vectors w/ different directions
 Combine by graphing
 Resultant vector - sum of all vectors
 Shows distance & displacement related but
different
Section 11.1 Assessment
 What is a frame of reference? How is it
used to measure motion?
 How are distance and displacement
similar and different?
 How are displacements combined?
 A girl who is watching a plane fly tells her
friend that the plane isn’t moving at all.
Describe a frame of reference in which the
girl’s description would be true.
Section 11.1 Assessment
 Should your directions to a friend for
traveling from one city to another include
displacements or distances? Explain
your choice.
 A spider is crawling on a wall. First it
crawls 1 m up, then 1 m to the left, and
then 1 m down. What is the distance the
spider crawled?
 What is the spider’s displacement?
Section 11.2
Speed and Velocity
p. 332
Have your
calculator on
your desk
Video
Can you describe the speed of the skaters?
What information is needed to determine
the speed of the skaters?
Speed - ratio of distance traveled to time
needed to travel that distance.
 SI unit
 meters per second (m/s)
 derived units:
 km/hr
 cm/s
Average speed
 entire duration of a trip,
 average speed - total distance traveled (d),
divided by total time (t)
Average Speed = total distance
total time
Or…..
Calculating average speed
Math Skills p. 333
Average Speed ( v )
 Avg speed doesn’t reflect most common
speed of trip
 stops, curves, hills
 Useful – tells how long trip will take
 If v is 60 mi/hr & destination is 120 mi, your
TOA is 2 hours
Calculating average speed
Math Practice p. 333
Instantaneous speed
Instantaneous speed (v) - rate object is
moving at given moment
 speedometers show instantaneous
speed
 100 mi/hr (160 km/hr)
Graphing Motion
 Distance-time graph
 Slope = change in vertical axis
change in horizontal axis
• Slope is speed of object plotted
Graphing Motion
 Slope (rise/run) = speed
 Calculate:
Distance v.s. Time of an RC car
 What can you
conclude about the
speed of the RC car?
Graphing Motion
Distance-time
graph
 4 segments (A-D) to find average speed for each
segment
 Calculate:
Driving speed of a car in rush hour traffic
D
C
 Describe the
speed of the car
in segment B?
B
A
Velocity
 Pilots and control
tower communicate
describing velocity of
planes
 Velocity describes speed and direction
 vector
 v changes if speed, direction, or both
change
Velocity
 Car traveling at constant speed (55 mi/hr)
 How would you describe its velocity?
 Direction changing on circular track, velocity
changing
Changing Velocities
 When velocities in same direction, add
together
 River velocity= 7km/hr east
 Boat velocity= 16km/hr east
Calculate:
16 km/hr east
7 km/hr east
Changing Velocities
 When velocities at rt angles, use Pythagorean
theorem to solve
a2 + b2 = c2
 plane= 400km/hr west
 wind speed= 25km/hr south
Calculate:
400 km/hr west
25 km/hr south
Science of NHL hockey – vectors 4:29
Section 11.2 Assessment
 You and a friend are watching a baseball
game on ESPN where the commentator says
“the pitcher’s velocity of 100 mi/hr is virtually
unhittable”. Your friend agrees. What do you
think?
 What does the slope on a distance-time
graph indicate?
Section 11.2 Assessment
 Does a car’s speedometer show
instantaneous speed, average speed, or
velocity? Explain.
 An Olympic swimmer swims 50.0 meters
in 23.1 seconds. What is his average
speed?
Section 11.2 Assessment
 A plane’s average speed between two
cities is 600 km/hr. If the trip takes 2.5
hours, how far does the plane fly?
Section 11.2 Assessment
 A discus thrower threw his disc 139
meters through the air. While in flight, the
disk traveled at an average speed of 13.0
m/s. How much time did the disk remain in
the air?
Section 11.3
Acceleration
p. 342
Have your
calculator on
your desk
Suzuki Hayabusa
What is acceleration?
 Remember velocity is speed w/ direction
 Acceleration - rate velocity changes
 Vector
 What is a rate? time it takes
Changes in speed
 green stoplight car moves forward
 acceleration (positive change in car’s speed)
pushes you back in seat
 red stoplight  speed decreases
 (negative change) you fall forward towards
dash
vectors_car_velocity_accel.notebook
Free-Fall
 Free-fall - acceleration toward Earth b/c
gravity
 Speed/velocity SI units is m/s
 Units for acceleration meters per second per second
or m/s2
 The 2nd “second” is
time needed to
change speed (rate)
Free-Fall
 a near Earth = 9.8 m/s
2
 bungee jumper will accelerate 9.8
meters per second every second
he’s in FF
 1 s of FF speed = 9.8 m/s
 2 s of FF speed =19.6 m/s (sped
up 9.8 m/s in 1 s)
 What is speed after 3 s?
29.4 m/s
after 3
seconds
If the Earth is moving, why
can I not feel it?
 body detects changes in speed
 Earth spin constant speed
 850 mi/hr at mid latitudes (faster at equator)
 Revolves 67,000 mi/hr
 2x bullet speed!
 1.6 million miles / day!
WOW!!!
Changes in Direction
a occurs if direction changes even if speed
constant
 Ferris wheel & carousel = constant speed
 accelerate b/c change direction
Changes in speed and direction
 roller coasters
 winding roads
Constant Acceleration
 straight line motion & speeding up / slowing
down - constant acceleration
 v of object changes same amt each sec
Indy car pulling G’s 3:00
Calculating Acceleration
 calculate acceleration for straight-line
motion using this equation:
Acceleration = change in velocity
total time
or…..
Velocity and
acceleration
1:58
(vf – vi)
t
venn diagram review.notebook
(vf – vi)
a
x
t
Math Practice #1 p. 346
 A car traveling at 10 m/s starts to decelerate
steadily. It comes to a complete stop in 20
seconds. What is its acceleration?
Math Practice #2 p. 346
 An airplane travels down a runway for 4.0
seconds with an acceleration of 9.0 m/s2.
What is its change in velocity during this
time?
Math Practice #3 p. 346
 A child drops a ball from a bridge. The ball
strikes the water under the bridge 2.0
seconds later. What is the velocity of the
ball when it strikes the water?
Math Practice #4 p. 346
 A boy throws a rock straight up into the air. It
reaches the highest point of its flight after 2.5
seconds. How fast was the rock going when
it left the boy’s hand? (acceleration is downward
b/c of gravity, but velocity is upward)
Acceleration of a Mercedes-Benz
 Volunteer timers – we will average the times
 How much time does it take to go from 0
km/hr to 200 km/hr?
Graphs of Accelerated motion
 Speed-time graph displays acceleration
 Slope of speed-time graph is acceleration
of object
Distance-Time Graphs
 Accelerated motion is represented by a curved
(non-linear) line on distance-time graph
 Slope (speed) greater after 3 sec than 1 sec
acceleration video 3:24
Instantaneous Acceleration
 Instantaneous
acceleration (IA) - how fast
velo changing at specific
instant
 Skateboarder continually
changes speed & direction
 his IA always changing
Instantaneous Acceleration
 Vector of skateboarder’s
acceleration can point any
direction
 Vector length represents
how fast velocity is
changing
 IA even if standing still and
acceleration vector zero
Section 11.3 Assessment
 Describe 3 types of changes in velocity.
Increase in speed, decrease in speed, change in
direction
 What is the equation for acceleration?
Acceleration = change in velocity
time
 What does the slope on a speed-time
graph show? acceleration
 Define instantaneous acceleration.
The change in an object’s velocity at any
specific instant