Linear Motion

1
Linear Motion

• Mr. Callan
• Physics
• Assignment Read Chapter 2
• Do all even questions on pages 25-27 (except
  activities) chapter review.
• Do problems 1-8 in Problem-Solving work book
  on pages 1-14 (WB 1-14)

2
Equations
3
QuizHow Fast are You Moving When You Are Sitting
Still?

• What is your observation?
• What do you need to know?

4
Hint 1

• At the equator the surface of the earth rotates
  around the center at about 1000 mph
• At our latitude the movement is about 650 mph.

5
Hint 2

• You are revolving around the sun at about 66
  thousand miles per hour,

6
Hint 3

• You are traveling around the center of the Milky
  Way galaxy at about 2 million miles per hour.

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Linear Motion

• Motion in a straight line. 1 dimensional
• Everything is in motion.
• Motion is a rate.
• Rate is a quantity divided by time.
• Since everything moves, motion is relative not
  absolute. A space shuttle in orbit moves at about
  8 km/sec.
• But it also move very slow.
• Review How fast is this in miles/hour?

8
Speed

• A measure of distance / time.
• The rate could be mi/hr, km/sec, ft/sec etc.
• Definition Speed is the distance covered per
  unit of time. Per means divided by.

9
Instantaneous Speed

• A car does not move at one speed. It changes from
  zero to its maximum speed.
• Your speedometer measures the cars instantaneous
  speed.
• It is the speed at any one point in time.

10
Average Speed

• Average speed is used to plan trips.
• It is the total distance traveled divided by the
  time it took to travel the distance.
• Average Speed total distance/time interval

11
Velocity

• Velocity and Speed are used interchangeably in
  everyday language.
• But THEY ARE NOT THE SAME.
• Velocity is speed in a given direction.
• Such as 60 mile per hour North.

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Constant Velocity

• No change in speed
• No change in direction
• Motion is a straight line

13
Changing Velocity

• Speed could be changing
• OR
• Direction could be changing.
• OR Both

14
Acceleration

• The rate of change of velocity.
• The change in velocity/time interval.
• OR the rate of change of speed.
• The change in speed/time interval.
• deceleration is the acceleration in the negative
  direction.

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Additional Assignment

• Always look at the questions in the yellow boxes.

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2.5 Free Fall How fast

• An apple falls from a tree. Does it accelerate
  while falling?
• What do we know?
• It starts from rest (velocity and acceleration
  0) then gains speed.
• The gain in speed indicates that the apple does
  indeed accelerate.

17
Free Fall Cont.

• Why does the apple accelerate? -Gravity
• In this course we generally neglect air
  resistance (friction).
• Therefore, we say that the apple is freely
  falling or is in free fall.
• Objects in free fall increase their their
  velocity by about 10 m/s each second.
• What does this mean?

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Free Fall

• a D v/ Dt 10 m/s per sec. or 10 m/s/s
• For objects in free fall a g
• More accurately g 9.8 m/s2
• Since g a D v/ Dt
• D v g Dt for an object starting at rest the
  the initial velocity (vi) zero, so the
  equation becomes v g Dt .
• If the initial time interval (ti) is set to zero,
  the the equation becomes vgt

19
Final Velocity with Initial Velocity

• If someone throws a ball, it has an initial
  velocity. Vi initial velocity
• To calculate the final velocity Vf, the initial
  velocity is added into the equation.
• Vf g Dt Vi
• Lets say a ball is thrown straight down at 2m/s
  from the top of Sear Tower. How fast is it going
  after 3 seconds?

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2.6 Free Fall How far?

• An object falling from rest is moving at 10 m/sec
  at one sec. But what is its average velocity?
  10/2
• Time (sec) Instant Speed (m/s) Ave. Speed
• 0 0 0
• 1 10
• 2 20
• 3 30
• 4 40

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Free Fall How Far

• The average velocity is the velocity we need for
  finding the distance. (vivf)/2vave
• d 1/2 gt2 Look at the units!
• meters1/2 m/(sec x sec) x sec sec

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Free Fall How far?

• Time (sec) Instant Ave. Distance
• 0 0 0 0
• 1 10 5 5
• 2 20 15 20
• 3 30 25 45
• 4 40 35 1/2gt2

23
Reaction Time

• A bill is 15.5 cm long so if your table mate
  places his/her thumb and finger over the center
  and you let go of the bill can your table mate
  catch the bill?
• No, the bill falls 8 cm in 1/8 of a sec. Your
  reaction time is much greater.

24
Lets Measure your Reaction Time

• Lab 2
• Find One and only one partner.

25
Hang Time

• Your hang time is related to how high you jump
• d ½ gt2
• Solve the vertical distance equation for time and
  then have your tablemate measure how high you can
  jump.

26
Graph Matching
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2.8 Air Resistance Falling Objects

• http//www.hq.nasa.gov/alsj/a15/a15v.1672206.mov

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Equations and Units

• vat, av/t, and ta/v
• vgt, gv/t and t v/g
• d1/2at2
• Reaction time (2d/a)1/2 , where ag9.8m/s2

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Chapter Review Due Thursday

• Do the even problems on pages 25-27
• WB Wednesday
• Test Friday