Motion in a line (linear motion)

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Chapter 3

• Motion in a line (linear motion)

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Motion Vocabulary

• A cat moves a distance of 10 meters (how far?) in
  5 seconds. What information do you KNOW from
  this? What can you calculate?
• ______(technically ____________) ______
• Most common units _______________________
• ____________ speed _________________
• This is the quantity scientists use. _______tells
  us how ___________________________________
• _______________.

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Speed/velocity questions

• Questions a car moves 20 meters/sec. How far
  does it go in
• 3 seconds? _______________
• 10 seconds? _______________
• 1 minute? _______________
• 1 hour? _______________
• Describe how something could move with constant
  speed but CHANGING velocity.

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When youre sitting completely still, are you
moving?

1. Yes
2. No

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Debrief

• Talk to your neighbors
• Did you get it right?
• Why or why not?
• Make sure you understand.

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Motions

• Daily motion Earths rotation once per __
• Speed varies ___ for Santa, __________for
  __________
• ______________________________
• Yearly motion Earths revolution once per __
• Distance 1AU ____
• Speed average _______________mph
• Direction _______________________________.
• Sun _______________________________-230 Million
  yr
• 28,000 light-year radius, speed 500,000 mph
• Studying this motion ? _________________________
• Galaxies moving relative to each other.
• ________________________________________________.

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Acceleration

• Acceleration any change in velocity
• ___________________________________
• __________________________________
• In everyday English, slowing down is called
  ________ but physicists use accelerating to
  mean _________________________________.
• Give some examples of things that are
  accelerating in the physics sense.

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Velocity vs. acceleration

• Identify the following as velocity (arm points
  right) or acceleration (arm points left)
• Going 55 mph
• Using the gas pedal on your car
• Rolling in a straight line
• Using the brakes on your car
• Using the steering wheel on your car
• Running 10 meters per second
• Things falling due to gravity.
• Things thrown upwards on their way up to the top

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Which does the human body feel?

1. Velocity
2. Acceleration

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Debrief

• Talk to your neighbors
• Did you get it right?
• Why or why not?
• Make sure you understand.
• For this question, the same is true
  for___________. They FEEL ___________.

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Accelerating changing velocity

• When things ____________________ ____________
  in a _______________ way
• Cars go from zero to ____ in ____ seconds.
• Thats an acceleration of _______________
• Sprinters run at a top speed of _________
  meters/sec (or _____mph).
• How long does it take to speed up? (Or slow
  down?)
• Calculate the accelerations.

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Airplanes travel at a constant speed of 400
miles/hr. Is the airplane accelerating?

1. Yes
2. No
3. Not enough information provided

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Debrief

• Talk to your neighbors
• Did you get it right?
• Why or why not?
• Make sure you understand.

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Two track demo

• See page 57, question 40.
• Clicker question coming
• Which reaches end of track first?

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Which ball reaches the end of the track first?

1. Same time
2. Ball on a straight path
3. Ball on the downhill/uphill path

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Debrief

• Talk to your neighbors
• Did you get it right?
• Why or why not?
• Make sure you understand.

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Acceleration changing an objects speed

• Ramp demo
• Imagine something accelerates at a constant rate
  of 2 miles/hr per second of motion. It starts at
  rest. Work with your neighbor.
• Initially, its speed is _____________
• After 1 second, its speed is ____________
• After 2 second, its speed is ____________
• After 3 second, its speed is ____________
• After 10 secs, its speed is ____________
• After 2000 secs, its speed is ____________
• Write a rule for the speed after T seconds.
• After you write your rule, notice the textbook
  gives an equation on page 47.

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A super-fast car and truck start at the same
place. The car goes 100 m/s (220 miles/hr)
always. The truck starts at rest and accelerates
1 m/s per HOUR. Will the truck ever catch the car?

1. Yes
2. No
3. Not enough information is provided

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Debrief

• Talk to your neighbors
• Did you get it right?
• Why or why not?
• Make sure you understand.

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_______________________________ _________ covered
more distance?

1. Car
2. Truck
3. Same
4. Not enough information is provided

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Debrief

• Talk to your neighbors
• Did you get it right?
• Why or why not?
• Make sure you understand.

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_______________________________ ______________ is
moving faster?

1. Car
2. Truck
3. Same
4. Not enough information is provided

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Debrief

• Talk to your neighbors
• Did you get it right?
• Why or why not?
• Make sure you understand.

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Calif. Science Standards for motion

• From California Science Standards, grade 2
• Students know the way to change how something is
  moving is by giving it a push or a pull. The size
  of the change is related to the strength, or the
  amount of force, of the push or pull.
• And from grade 8
• Students know the velocity of an object must be
  described by specifying both the direction and
  the speed of the object.
• Students know changes in velocity may be due to
  changes in speed, direction, or both.

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Gravity near ground

• Free fall
• Toss something up, what happens on way up?
• Drop something, what happens on way down?
• When things fall, measure ________________ for
• _______________
• _______________
• _______________________________________of
  falling.
• Paper/pen experiment
• _____________________________________for ___
  __________________________________________
• Unless there are __________, such as
  _____________
• Then were dealing with NET force, not gravitys
  force.
• Galileo observed this (in Pisa). Galileos
  observations helped Newton formulate ideas.

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From Apollo 15 missionMen on the Moon

• Show the hammer-feather movie
• Search internet for this if you want to see it at
  home.

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Gravitational acceleration

• g 10 m/s per second or 22 mph per sec
• Drop something from rest. How fast will it be
  moving after
• 1 sec _______________
• 2 sec _______________
• 10 sec _______________
• T sec _______________
• After writing your rule, compare yours to the
  books version on p. 48
• 10 m/s2 (on Earths surface) is abbreviated g
• More precisely its 9.8 m/s2.

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Free fall questions

• What happens to an object if you drop it at rest?
• How quickly?
• If you toss something straight upwards
• What happens on the upwards part of motion?
• How quickly?
• What happens on the downward part?
• How quickly?

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How fast is something moving at the top of the
motion after being thrown upwards? The answer
depends on

1. Nothing it is moving w/ speedzero
2. how fast it was thrown
3. How long you wait
4. how fast thrown how long you wait

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What is the acceleration at the top of the motion
after being thrown upwards?

1. Zero
2. g
3. Not enough information provided

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You have two spheres of equal size and
smoothness, and you can ignore air resistance.
One is heavy, the other much lighter. You hold
one in each hand at the same height above the
ground. You release them at the same time. What
will happen?

1. The heavier one will hit the ground first.
2. They will hit the ground at the same time.
3. The lighter one will hit the ground first.

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Same objects. How does the acceleration of
gravity compare?

1. The heavier one has a larger gravitational
   acceleration.
2. They have the same gravitational acceleration.
3. The lighter one has a larger gravitational
   acceleration.

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Same objects. How does the force of gravity
compare? Be careful!

1. The heavier one has a stronger gravitational
   force.
2. They have the same gravitational force.
3. The lighter one has a stronger gravitational
   force.

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California Elementary School Science Standards
for gravity

• From California Science Standards, hgih school
• Students know the relationship between the
  universal law of gravitation and the effect of
  gravity on an object at the surface of Earth.

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Summary

1. Definitions speed, velocity, acceleration
2. Differences between these three
3. Simple computations of speed accel.
4. Gravity is an acceleration
5. All things freefall with same acceleration