11/18/2010 Erica and Kyle’s Data Cady and Katie’s Data

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11/18/2010

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Erica and Kyle’s Data

2 4 6

V(cc) of air

Y = A + B * X

Parameter Value Error

--------------------------------------------------------

A

B

-211.68571

25.85714

5.87999

0.65465

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R SD N P

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0.99872

0.83666

6 <0

8 10

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Cady and Katie’s Data

2 4 6

V(cc) of air

8

Y = A + B * X

Parameter Value Error

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A -202.20717

25.81236

B 26.03586

3.00741

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R SD N P

----------------------------------------------

0.97434

3.8903 6 9.7

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Andrea and Andrea's Data

2 8 4 6

V(cc) of air

Y = A + B * X

Parameter Value Error

--------------------------------------------------

A

B

-208.33558

26.57666

23.35177

2.70483

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R SD N P

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0.97991

3.55593

6

10

Quick Quiz

What is the most likely cause of error in the determination of Absolute Zero done in lab?

A. Human error

B. Thermometer readings

C. Syringe readings

D. Some uncontrolled factor, like water vapor in the air in syringe

E. Gravity

Quick Quiz—all correct

What do you think would benefit you the most during the last lab period next

Tuesday Nov. 23:

A. Measuring “g”, the acceleration of gravity by graphing the period of a pendulum as you change the length?

B. Touring physics research laboratories and writing a sentence on each of10 key points learned in the tour?

You already know Galilean Relativity

To describe an event must choose a frame of reference

According to Galilean Relativity, the laws of mechanics are the same in all inertial frames of reference

An inertial frame of reference is one in which Newton’s Laws are valid

Objects subjected to no forces will move in straight lines

Galilean Relativity – Example

There is a stationary observer on the ground

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11/18/2010

Galilean Relativity

What can we conclude?

The two observers disagree on the shape of the ball’s path

Both agree that the motion obeys the law of gravity and Newton’s laws of motion

Both agree on how long the ball was in the air

Conclusion: There is no preferred frame of reference for describing the laws of mechanics

Galilean Relativity and EM Radiation

The Galilean observer should measure the speed of the pulse as v+c

Actually measures the speed as c

EM waves and the Luminiferous Ether

19 th Century physicists compared electromagnetic waves to mechanical waves

Mechanical waves need a medium to support the disturbance

The luminiferous ether was proposed as the medium required for light waves to propagate

Present everywhere, even in empty space

Massless, but rigid medium

Could have no effect on the motion of planets or other objects

Associated with an ether was an absolute frame where the laws of e & m take on their simplest form

Since the earth moves through the ether, there should be an “ether wind” blowing

If v is the speed of the ether relative to the earth, the speed of light should have minimum or maximum (a) value depending on its orientation to the “wind”

Michelson and then Morley Test It! (1881)

Invented the Michelson

Interferometer

Arm 2 is aligned along the direction of the earth’s motion through space

Huge granite slab floated on pool of mercury

The interference pattern of

2 beams was observed with interferometer at two positions rotated by 90°

The effect should have been to show small, but measurable, shifts in the fringe pattern because of ether wind

Einstein’s Principle of Relativity resolves problems without ether

Postulates (1905)

The Principle of Relativity: All the laws of physics are the same in all inertial frames

The constancy of the speed of light: the speed of light in a vacuum has the same value in all inertial reference frames, regardless of the velocity of the observer or the velocity of the source emitting the light

 No preferred inertial reference frame exists

 It is impossible to detect absolute motion

 There is no such thing as absolute length

 There is no such thing as absolute time

 Events at different locations that are observed to occur simultaneously in one frame are not observed to be simultaneous in another frame moving uniformly past the first

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11/18/2010

Simultaneity – A Thought Experiment

Quick Quiz

An inertial reference frame is one which:

A.

B.

C.

D.

E.

Is rotating

Is always stationary

Is at rest or moving at a constant velocity

Is accelerating

Is a fiction of the human mind

After some time

The light signals reach observer O at the same time

He concludes the light has traveled at the same speed over equal distances

Observer O concludes the lightning bolts occurred simultaneously

By the time the light has reached observer

O, observer O’ has moved

Light from B’ has already moved by the observer, but light from A’ has not

The two observers must find that light travels at the same speed

Observer O’ concludes the lightning struck the front of the boxcar before it struck the back (not simultaneous events)

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