Lets Talk Motion

1
Lets Talk Motion!

• Summarize what you know,or learn something
  new!(its all good)

2
Distance vs. Displacement

• Distance is how much total ground an object
  covered.
• Displacement is a vector (direction matters!), so
  it only describes the change in position from
  start to finish.

3
Think About This

• When Danica Patrick drives the Indy 500
• her distance would equal 500 miles,but her
  displacement would be 0 miles!

• Her odometer would show 500 miles, but
  because the start/finish line are in the same
  place there is no displacement.

Photo www.wikepedia.org
4
Types of Speed

• Instantaneous speed at a particular point in
  time
• Average speed of motion when speed is
  changing.

5
Speed Formulas

• Speed
• Average Speed
• Units are m/s, miles/hour, km/hr, etc.

6
Think About This

• Most speeding tickets calculate speed over a
  distance ( average speed)
• Lets stop and practice rearranging the speed
  formulas!

Cartoon ?www.pointts.com
7
What is Velocity?

• Velocity is speed in a specific direction.
• If you say I was driving 60 mph, you are
  describing speed.
• If you say I was driving 60 mph north on 355,
  you are describing velocity.
• Units are still m/s, miles/hour, km/hr, etc.

8
It Sounds Weird But

• Any time you change direction, you are also
  changing velocity -- even if your speed doesnt
  change!

The horses on a carouselare constantly
changingVELOCITY even though their speed is
constant.
Photo www.salemcarousel.org
9
Think About This!

• Saying Lance was pedaling 22 mph describes his
  speed.
• Saying Lance was pedaling 22 mph north into
  Paris describes his velocity.

Photo ?www.hcgtv.com
10
And Acceleration?

• Acceleration is the rate at which velocity
  changes.
• If acceleration is positive, youre speeding up
• If acceleration is negative, youre slowing down
• Remember An object accelerates any time it
  changes speed or direction.

11
Roller coasters accelerate

• When they change speed
• When they change direction

Photo ?www.nolimitscoaster.com
12
Myth Alert!!!

• You accelerate even when youre slowing down!
• Slowing down is acceleration with a NEGATIVE
  slope on a velocity vs. time graph.

13
Acceleration Formula

• Acceleration
• Acceleration Watch the units! Now its m/s2!

14
Lets Review the Labs!

• Take notes, try sample problems, and rewrite the
  ideas in your own words!

15
Position vs. Time Graph(One Photogate)

• The slope of the line on a position-time graph
  is the speed, because speed distance
  time

16
Position vs. Time Graph(Two Photogates)

• Notice when you compare the speed at positions
  along the ramp, the slope gets steeper, showing
  the car is moving faster toward the bottom of the
  ramp!

17
Velocity vs. Time

• The slope of the line on a velocity-time graph
  is the acceleration, because acceleration
  change in velocity time

18
Try This One!

• Calculate the acceleration shown on this graph!

Answer 4 m/s2
19
The Tough Part!

• Now lets compare graphs to each other. (This is
  tricky, so ask if you dont quite see it right
  away).
• Lets compare a distance vs. time graph to a
  speed vs. time graph

20
Position (Distance) vs. Time

• The SLOPE of this line tells you how fast the
  car is driving (speed).

21
Velocity (Speed) vs. Time

• The SLOPE of this line tells you how fast the
  cars speed is changing (velocity).

22
Now Side by Side
Notice that the same data shows TWO
differentrelationships when you change the
graphs! The car is moving (P/T) but it since the
speed is constant, it is NOT accelerating (V/T).
23
Now You Try These!
24
AdvancedPosition vs. Time Graph

• Segment A shows the car driving NORTH at a
  constant speed.
• Segment B shows the car stops for 3 seconds.
• Segment C shows the car driving SOUTH toward the
  starting point.

Position vs. Time
B
A
C
25
AdvancedSpeed vs. Time Graph

• Segment A shows the car accelerating at a
  constant rate.
• Segment B shows the car driving at a constant
  speed (on this graph, a straight line does not
  mean it stopped!
• Segment C shows the car accelerating (but this
  time its slowing down!) at a constant rate.

Speed vs. Time