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Physics Unit 1�MOTION & SPEED

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Review of Motion (check your lab)

1. Motion is the __________________ over time.

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2. Position is _____________________�

3. Reference Point

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4. Frame of Reference

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change of position

an object’s location

object/location to which you compare other objects/locations

background used to see

if something is

in motion

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2 Ways to Describe Position

1. Use DISTANCE and DIRECTION

Ex) San Diego is 3,000 miles WEST of Raleigh

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2. Use Latitude & Longitude

Ex) San Diego 320 44’N; 1170 10’W

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Ways to Describe Motion

  • Speed (today’s topic)

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  • Frame of Reference

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What object is the Frame of Reference ?

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Speed

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What is speed?

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What is Speed?

  • Speed is the distance something moves in a given amount of time.

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How Do We Calculate Speed?

1. Need to know DISTANCE and TIME

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s= Speed

d= Distance

t= Time

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Units of SPEED…�(distance over time)

Meters/Second = m/s

Ex. 3m/s

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kilometers/hour= km/h

Ex. 4km/h

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Sample Problem #1

  • A girl biked 8 meters in 2seconds. What was her speed?

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Sample Problem #1

Formula-

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Substitute-

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Solve:

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Answer:

Speed = ? �Distance= 8 meters �Time= 2 seconds

s = 8m

2s

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S = 4m/s

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Sample Problem #2

  • A wheelchair racer completes a 100 meter course in 20 seconds. What is his speed?

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Sample Problem #2

Formula-

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Substitute-

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Solve-

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Answer-

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Speed = ? �Distance= 100 meters�Time= 20 seconds

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S = 100 m

20 s

S = 5 m/s

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Sample Problem #3

  • A cheetah runs 90 meters in 9 seconds.

What is his speed?

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Sample Problem #3

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Formula-

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Substitute-

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Solve-

Answer-

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Speed = ?

Distance = 90 meters

Time = 9 seconds

90 meters

9 seconds

s = 10 m/s

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Why do you want an average speed?

1. Speed is NOT always constant.

2. Ex: Running a race…

    • Sometimes you speed up
    • Sometimes you slow down

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Average Speed = Total Distance

Total Time

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Example:

Lap

Distance

Time

Speed

1

400 meters

83 seconds

4.8 m/s

2

400 meters

81 seconds

4.9 m/s

3

400 meters

79 seconds

5.1 m/s

4

400 meters

77 seconds

5.2 m/s

Average speed

1600 meters

320 seconds

5m/s

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DISTANCE –TIME GRAPHS

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DISTANCE –TIME GRAPH

  • Describes an object’s motion by plotting distance traveled against time (that’s speed!)

DISTANCE (m)

TIME (s)

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* TIME on X-axis

** DISTANCE on Y-axis

*** SLOPE of the line is SPEED !!!

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Tip #1

SLOPE = SPEED

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slope = change in “Y”

change in “x”

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speed = change in “distance”

change in “time”

Y

X

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IMPORTANT GRAPH TIP #2

Sloped lines shows object moving at constant speed

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Tip #3

Flat line (no slope) means?? speed = 0 m/s

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Tip #4

Steep lines mean faster speeds

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Distance vs. Time Graph

  • What does this graph tell us about the speed of the helicopter?

Answer: SPEED is changing because SLOPEs are changing.

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HOMEWORK:

  • Add another column to the end of data tables A and B.

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  • Calculate the speed for each trial on both data tables.

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  • Make Flashcards:
      • Position
      • Frame of reference
      • Motion
      • Speed & Speed formula
      • Reference Point

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Take out your “Walk in the Park” lab and put it in the middle of the desk.

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�Q: What information does this graph give?

Q: WHAT DOES A NEGATIVE SLOPE MEAN ?

REVIEW

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Velocity

I’m lost can you give me some directions?

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Consider the following….

Ms. Thomasson tells Mr. Moore and Mr. Beko to get in their cars and drive 100 miles at 45mph.

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  • Will they end up in the same place?
  • Discuss your ideas with your group.

Velocity notes

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Velocity is…

Speed with a ____.

Specific Direction

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Speed: 5m/s

Velocity: 5m/s North

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Vector is a…

  • quantity that has both SIZE (magnitude) and DIRECTION

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    • Ex: VELOCITY and ACCELERATION

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Acceleration

  • Change in velocity.
  • Can be a positive # or a negative #.
  • What would it mean if the answer was negative?

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  • (Write this on back of your velocity notes sheet)

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Velocity vs. Speed

  • Since velocity includes SPEED and DIRECTION, it is possible for 2 objects to have the same speed but different velocities

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  • Ex: Car (30km/hr North)

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Car (30km/hr South)

When direction is important, use VELOCITY

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Create a Venn diagram to compare and contrast velocity and speed

Velocity

Speed

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Terms for Venn diagram

  • Speed
  • Distance
  • Direction
  • Is a vector
  • No direction
  • Time
  • Formula
  • Motion

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TOC #?

  • Answer # 1-5 with your group

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  • HW – Challenge & Extension: interpreting a speed graph