# Length contraction??? (1 Viewer)

#### shinji

##### Is in A State Of Trance
SL33pY said:
im a 0.3 person... but seriously,, this is getting out of hand,, so many replies for one question... could someone possibly get a response from a teacher?!
or are there any mods in uni browsing this thread that could help us out here?

i can see the logic from both sides of the argument... so i am really unsure ><
in uni, they don't talk about length contraction in physics due to the fact it's dodgy
[i heard it off my friend who's doin nanotech in unsw. he got 99.35 for his uai]

yeah, he said that lookin at the wording, the length from scientists' perspective is gonna be more.
hence, 0.3m

yeah, he said the wording of the questions was crap as well~~
*there's no s uch thing as an electron's frame of reference as it is a wave, not a particle*

#### macoboi

##### Member
shinji said:
*there's no s uch thing as an electron's frame of reference as it is a wave, not a particle*
It's both.

#### bboyelement

##### Member
macoboi said:
It's both.
and light travels at speed of light whereas the question clearly states that 0.6c which means that its a particle.

#### dunno04

##### Member
bboyelement said:
and light travels at speed of light whereas the question clearly states that 0.6c which means that its a particle.
the electron travel on 0.6c

Speed of light is the same for all frame of reference.

#### Irskin

##### Member
The answer is 0.3m, trust me.
Whoever says it is 0.19 is suggesting that the whole cathode ray tube is moving at 0.6c. The length of the electron will contract relative to the scientists but it is the only thing moving inside the tube. No matter what speed the electron moves at relative to the scientists the length between the cathode and anode is a constant, it doesn't change.

Look, if the scientists use a ruler and meausre the length to be 0.19m, why the fuck would that length increase to 0.24m relative to an electron travelling at 0.6c??? That's impossible.

Answer = 0.3 metres as the length contracts in the electron's frame of reference

#### ReaL~

##### Member
arghh i put 0.196...
its still a valid answer rght

i thoguht the electron travled a length 0.24 in its referecne and the obersvers outside saw a contraction of 0.196 D:

#### joe1016

##### Member
ahhh, this is so confusing because people who put 0.3 are CONVINCED THEY ARE RIGHT and the people who put .192 ARE CONVINCED THEY ARE RIGHT

i originally put the answer as .192 because if you use the same thingos for Lo and Lv as u did for the mass dillation you got the answer of .192

cos im pretty sure i got the mass dilation one right

except then i thought i read a sample answer about a question on space travel which said something alon gthe lines of "the inplications of travelling at a relativistic speed means that although the mass gets heavier, the distance to the destination gets shorter" ahhh im so completely shite at this topic. it's mindbending.

but now im thinking about it. from the part a) to part b) were we swapping our frames of reference, so therefore we had to swap our Lv and Lo over from the last time? maybe .30 was right???

ahhh so confused. and yes i am aware that i changed my mind half way through my post

#### Rax

##### Custom Me up Scotty
Ok....I dont know what is going on as I aint going to read this entire thread (My dl limit is right on max, damn cheap parents/telstra).

The electron is moving at 0.6c . Good. Now from its frame of reference, it sees the laboratory moving at this speed, so the lenghth of the tube (in reference to the laboratory) is contracted for the electron and the length for the tube is 2.4m (which is given)

Now for the laboratory frame of reference the electron is moving at 0.6c, not the actual tube itself, so in fact the length of the tube will be larger than in the frame of reference of the electron.

In the laboratory frame of reference, it is the electron which undergoes the length contraction, not the tube.

Which means when you sub in the values you swap them which results in getting the result (Which I hope to damn hell is right) of 0.3m
And yep, I hope this clarifies this all once and for all.

Hope everyone is happy (Well the people that got 0.192 wont be happy)

#### SL33pY

##### ceo of the banana factory
shinji said:
in uni, they don't talk about length contraction in physics due to the fact it's dodgy
[i heard it off my friend who's doin nanotech in unsw. he got 99.35 for his uai]

yeah, he said that lookin at the wording, the length from scientists' perspective is gonna be more.
hence, 0.3m

yeah, he said the wording of the questions was crap as well~~
*there's no s uch thing as an electron's frame of reference as it is a wave, not a particle*
cool thx man thats really helpful... so confusing cos both sides are putting forward pretty strong arguments... and plus i seem to have lost the question sheet so i cant read over it again (plus i dont want to )

#### shinji

##### Is in A State Of Trance
SL33pY said:
cool thx man thats really helpful... so confusing cos both sides are putting forward pretty strong arguments... and plus i seem to have lost the question sheet so i cant read over it again (plus i dont want to )
it's all good~~

yeah.
i rekkon BOS exam writers are crackheads

#### Glen88

##### Member
I concede that it is verly likely 0.3, based on a similar type of question:

A space ship travels to Alpha Centuri which is about 4 light years away from earth. How far does this distance appear to you if you are on a space ship traveling at 0.99c ?

The answer was 0.56 light years. Which means the external frame has to observe a longer distance than the inertial frame. Which means it has to be larger than 0.24. Thus, 0.3.

I'm assuming the information on this link is accurate.

Source: http://www.glenbrook.k12.il.us/gbssci/Phys/Class/relativity/U7l4e.html
Question 2 on that page.

#### macoboi

##### Member
Glen88 said:
Exactly from the exam:

The distance between the anode and the screen, as measured in the electron's
frame of reference is 0.24 m.
Calculate this distance as measured in the laboratory frame of reference.

Accept it...I'm just...right.

so we dont have to accept it anymore?

Pretty much.

#### dunno04

##### Member
macoboi said:
so we dont have to accept it anymore?

Lol..
That's Right!

xD

#### StYlez-

##### New Member
OWN3D.

suck on that u 0.192m mofos

#### macoboi

##### Member
Glen88 said:
Pretty much.
ah well, a good debate is still worth it.

good luck with the rest of the exam, i'd say thats only one mark lost

#### charismo

##### New Member
yorky said:
oy genius
if u are travelling as the electron u will not see your mass increase, time will pass normally relative to you, and you cant see your length contract, u can believe you got it right but im telling u its wrong, good luck anyway with that mate, lo is .24 x .8 = .192, suck it up and read ur notes boys, 3 marks down the drain, u may get one for effort. it is impossible for an object to see a contraction in length, because to it the craft appears normal, we see the contraction, take it.
aha you fucking dumbass... the electron isn't witnessing its own length contract... i love how your so cocky about your wrong answerr, it just makes you look like more of a tool... lo = 0.3.. why would the legnth in the reference frame of the scientists contract when they're not moving?

#### angmor

##### momentica-one.deviantart.
You Stupid Idiots Lol You Are Still At It. Read The Bloody Question The Electron Is Accelerating In A Different Frame How Can The Length Be The Same? Lmao

#### ch355fr3ak

##### New Member
a Gedanken is a thought experiment, which means einstein only used logic to calculate his length contraction experiments. Think about it, light is constant, therefore everything else must change (aduh).

Newton said a person in an inertial frame of reference cannot tell whether they are moving or not. Thus, if the electron did an experiment to measure light, since he is going faster, that means length for him must increase as well so that light will have the same value. V=d/t Thus, his measurements of 0.24m are longer than the stationary ones in the lab. that means the lab guys have less, approximately 0.192m. that's just using the logic that light is constant though. if it isn't, you'd probably get 0.3m. but probably my logic is stuffed up.