ap physics chp 28
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AP Physics Chp 28. Event – physical occurance Reference Frame – x,y,z axes and time Inertial reference frame a=0 and Fnet =0. Postulates of Special Relativity 1) Laws of Physics are constant in every inertial reference frame - PowerPoint PPT PresentationTRANSCRIPT
AP Physics Chp 28
• Event – physical occurance
• Reference Frame – x,y,z axes and time
• Inertial reference frame a=0 and Fnet =0
• Postulates of Special Relativity• 1) Laws of Physics are constant in every
inertial reference frame
• 2) Speed of light in a vacuum is c regardless of how fast the source and/or observer are moving relative to each other
• Absolute velocity?
• Luminiferous Ether
• Time Dilation
• ∆to is the observers time that is at “rest”• ∆t is the time for observers that are in motion
compared to the “event”• v is the relative velocity between the two
observers• c is 3.00 x 108 m/s
2
21o
vt t
c
• Length contraction
• Lo is the proper length – distance at rest with object
• Only in direction of motion
• Proper doesn’t mean “correct” or “absolute”
2
21o
vL L
c
• If you fly to Mars at 0.8 c and it takes 182 seconds to get there for those on the spaceship, how long does it seem for us left on earth? And if the ship is 1500 m long what length would it appear while moving?
2
21o
vt t
c
2
2
(0.8 )182 1
cs t
c 303t s
2
21o
vL L
c
2
2
(.8 )1500 1
cL m
c
900L m
• Relativistic Momentum
• p= mv for low velocity situations
2
21
mvp
vc
• Energy
• Eo=mc2 this is the rest energy
2
2
21
mcE
vc
• E = KE + Eo
• KE = E - Eo
22 2
2 2
2 2
11
1 1
mcKE mc mc
v vc c
• A change in energy causes a change in mass.
• Often it is too small to notice.
• Total Energy and Momentum
• E2 = p2c2 + m2c4
• Why is c the maximum? KE vs work
• Relative and Relativistic Velocities
• Tossing a ball from a moving vehicle
• Vab = Vac + Vbc Ex. 22 m/s + 5 m/s = 27m/s
• Velocity addition formula
21
ac cbab
ac cb
v vv
v vc
• If the large haldron collider can get a proton up to 0.9999c what is the classical momentum and what is the relativistic momentum for the proton?
• Classical• p = mv = 1.67x10-27Kg (0.9999) 3x108m/s• p = 5.01 x 10-19 Kgm/s
• Relativistic
• p= 3.5x10-17 Kgm/s so momentum is greater
27
2 2
2 2
(1.67 10 )(0.9999 )
(0.9999 )1 1
mv x cp
v cc c
• What are the rest energy, total energy, and kinetic energy for the accelerated proton?
• E0 = mc2 = (1.67x10-27Kg)(3x108m/s)2
• E0 = 1.44x10-10 J
27 28
2 2
2
1.67 101.06 10
0.99991
x cE x J
cc
• KE = E-E
• KE = 1.06x10-8 J - 1.44x10-10 J = 1.05 x 10-8 J