Time Dilation (2 Viewers)

[velox]

In the jacaranda book it states:

"*The length of an object measured within its rest frame is called its proper length. Measured by observers in relative motion the length, will always be shorter."

Does this mean that if I measure the length of a 30cm stationary ruler it will be 30cm. Whereas if the 30cm ruler is travelling at the speed of light its length will be <30cm?

What does it mean when it says "observers in relative motion" Does that mean the observers are travelling at the same speed?

TIA

 

[Xayma]

No it means if the observers are travelling relative to the object.

 

[AntiHyper]

i think they're travelling with the object, i guess with the same vector velocity

 

[Xayma]

Antihyper: a relative movement must occur for the length to be shorter as seen by the formula.

Wrx: at the speed of light its length is 0 at velocity it is smaller.

 

[KFunk]

If you are travelling in the same frame of reference as the ruler then you will measure it as having it's proper length. When they say "observers in relative motion" to the object they mean: Observers who, relative to the ruler, are in motion.

If I am then a stationary observer on earth and I see a 10,000m ruler fly past in space then the faster it goes, the more its length will contract in the direction of its motion.

 

[velox]

I see. So basically if i am in motion relative to the ruler, and the ruler is moving. I can be stationary. Is that right?

 

[JamiL]

yer relative to the ruler. so it will stay the same length from your perspective. its call and inertial frame of referance. if the ruler speed is approching c (it canot equal 2 c) it will be smaller. that also goes 4 time dilation and mass (exept mass increase at speed aproching c)

 

[JamiL]

ps ur not stationary, there is no way of telling... cos the earth rotates around the sun. the sun spirals around in the milky way. the milky way is moving outwards... etc. call it an inertial frame of referance, relative to......

 

[KFunk]

A perfect example of when not 2 substitute '2' and '4' 4 their sounding words.

 

[Xayma]

I see. So basically if i am in motion relative to the ruler, and the ruler is moving. I can be stationary. Is that right?

It doesn't matter as all motion is relative. No way to know which is moving and which is stationary, unless you are looking relative to a point you consider stationary.

 

[velox]

ok thanks guys, and JamiL, I had no idea what you were saying

 

[MuffinMan]

havent done this topic yet but how can time dialation work...
e.g. you wait 1s on a 0.9999999999c spaceship and someone observing has already 10 mins of their time passed. In physics terms this is possible but seriously practically its so weird...and length and mass dialation also...i've read jacaranda for that topic and i still dont quite get it

 

[wanton-wonton]

The thing I don't understand is, why is it only the length decreases and not the height/width of something?

 

[lfc_reds2003]

Does this mean that if I measure the length of a 30cm stationary ruler it will be 30cm. Whereas if the 30cm ruler is travelling at the speed of light its length will be <30cm?

TIA

If the ruler was travelling at c, the length would contract to 0!!!!!! HAHAHAHAHA

U should simply say at a high speed (e.g. 1/2c)

 

[zeropoint]

If the ruler was travelling at c, the length would contract to 0!!!!!! HAHAHAHAHA

U should simply say at a high speed (e.g. 1/2c)

Funnily enough, it's true. In the limit that v --> c, the ruler shrivels up into a plane figure.

The thing I don't understand is, why is it only the length decreases and not the height/width of something?

Length contraction in both dimensions leads to paradoxes, so it can't be true.

 

[M-turkey]

An example of relative movement is when your observing cars.

Stand next to a highway and watch the cars got past at "high-speed", you can have a relative velocity 110 km.h (the cars are moving that speed and compared to them your stationary).

If you then get into a car, and travel next to the same car, your both moving at 110 km/h (that would be relative to the ground). However you and the other car now have a relative velocity of 0.

Even through you are considered as moving at 110 km/h, compared (relative) to the other car, you are moving at 0. Because you are moving at the same speed.

Although this only works if you are both moving in the same direction.

 

[KFunk]

Length contraction in both dimensions leads to paradoxes, so it can't be true.

Length contraction in one dimension leads to paradoxes .

 

[zeropoint]

Length contraction in one dimension leads to paradoxes .

Hmmm, nope

 

[KFunk]

Hmmm, nope

Try and make two frames of reference agree on the length of an object and see what happens .

 

[Xayma]

Just because they observe different lengths doesn't mean there is a paradox. They are both right from their frame of refrence.