[guest39538]

Hello, I was asked a question by my 15 year old cousin and did not know what to answer.

He ask's

a Journey from A to B takes 1 second to travel at v=c

a journey from B to A takes 1 second to travel at v=c

distance (d) = X=?


net difference d/ t = ?

[Colin2B]

net difference d/ t = ?

you must have misunderstood the question, d/t is not a difference it is a speed if d is the distance (easily calculated using the speed of light).
You need to go back and ask for clarification.

PS - Net (or Nett in US) means a part of something, like Net income is income after deductions such as tax.

[guest39538]

net difference d/ t = ?

you must have misunderstood the question, d/t is not a difference it is a speed if d is the distance (easily calculated using the speed of light).
You need to go back and ask for clarification.

PS - Net (or Nett in US) means a part of something, like Net income is income after deductions such as tax.

I have asked and he says, he was asking about the net difference  between the two travelling bodies d/t

[Colin2B]

I have asked and he says, he was asking about the net difference  between the two travelling bodies d/t

there is no net difference the distance is the same, the speed is the same. If you want to consider these as vectors, you would define one as +ve and the other -ve, net difference 0.
Always happy to help with homework questions by giving hints, but in this case I still don't understand the question.

[guest39538]

I have asked and he says, he was asking about the net difference  between the two travelling bodies d/t

there is no net difference the distance is the same, the speed is the same. If you want to consider these as vectors, you would define one as +ve and the other -ve, net difference 0.
Always happy to help with homework questions by giving hints, but in this case I still don't understand the question.

Well I also thought the net difference was 0.   I think you answered the question, thanks Colin. 

A question of my own, why would you define -ve and +ve , is this to show the invert velocity?

what does the e mean?

and how would you express net difference in a symbol form?

[Colin2B]

A question of my own, why would you define -ve and +ve , is this to show the invert velocity?

No just direction.

what does the e mean?

+ve is just shorthand for positive.

and how would you express net difference in a symbol form?

Not aware of a symbol

[guest39538]

A question of my own, why would you define -ve and +ve , is this to show the invert velocity?

No just direction.

what does the e mean?

+ve is just shorthand for positive.

and how would you express net difference in a symbol form?

Not aware of a symbol

arrghh I see. So would I express for the above question


+ve=c
 
-ve=c
 
d=x
 
net difference t=0

Explaining a back and forth journey?

[Colin2B]

d=x
 
net difference t=0

Explaining a back and forth journey?

No, how can t=0 if you went there and back?

If you went there and back then d=2x and time =2t

[guest39538]

d=x
 
net difference t=0

Explaining a back and forth journey?

No, how can t=0 if you went there and back?

If you went there and back then d=2x and time =2t

I think you may of misunderstood or I have not explained greatly.

We were individually accessing two trips, the first trip from A to B then the second return trip of B to A , and calculating the net difference in time of each trip at constant velocity of c in either direction.

 

[Colin2B]

OK, this confused me:
"net difference d/ t = ?"

[guest39538]

OK, this confused me:
"net difference d/ t = ?"

Yes I probably should of put


net difference d/t^2  =0  or ∑(+ve⊥-ve)=Δv=(d/t^2)=0


To show both  journeys was equal in every aspect.   Would that be more understandable?

[alancalverd]

The important thing about the question is the realisation (following the experimental discovery) that c is constant regardless of direction, so A-> B = B->A in every respect.

Obviously d = 300,000,000 km or thereabouts.

[guest39538]

The important thing about the question is the realisation (following the experimental discovery) that c is constant regardless of direction, so A-> B = B->A in every respect.

Obviously d = 300,000,000 km or thereabouts.

Yes indeed the importance is to realise that c is constant regardless of direction and a set length of x in either direction the photons would take the exact same amount of time to arrive at each others destination.   


Would you say that at the exact half way point of X would be the exact position of passing photon's from each direction?

[evan_au]

how would you express net difference in a symbol form?

In mathematics, physics and chemistry, the Greek letter Delta ("d" sound) is often used to represent a difference:

• "Δ":Capital Delta
  
• "δ": lower case delta
  

Sometimes the equivalent English letter "d" is used to represent a infinitesimal difference (as in velocity=^ds/_dt).
...and a "curvy d" () in more complicated scenarios.

[guest39538]

how would you express net difference in a symbol form?

In mathematics, physics and chemistry, the Greek letter Delta ("d" sound) is often used to represent a difference:

• "Δ":Capital Delta
  
• "δ": lower case delta
  

Sometimes the equivalent English letter "d" is used to represent a infinitesimal difference (as in velocity=^dt/_dt).
...and a "curvy d" () in more complicated scenarios.

Then maybe simply ^dt/_dt=0 net difference?

[Colin2B]

Then maybe simply ^dt/_dt=0 net difference?

no, ^dt/_dt=1

for a difference you have to subtract eg t₁-t₂=δt

[guest39538]

Then maybe simply ^dt/_dt=0 net difference?

no, ^dt/_dt=1

for a difference you have to subtract eg t₁-t₂=δt

In my scenario

t₁-t₂=o

[jeffreyH]

Then maybe simply ^dt/_dt=0 net difference?

no, ^dt/_dt=1

for a difference you have to subtract eg t₁-t₂=δt

In my scenario

t₁-t₂=o

You can't simply subtract t2 from t1. Both of the time intervals are in the same direction since time does not go backwards. You gain nothing from the operation. It would be different if the time component was part of a velocity calculation. As that has a well defined direction since it is a vector.

[Colin2B]

You can't simply subtract t2 from t1. Both of the time intervals are in the same direction since time does not go backwards. You gain nothing from the operation. It would be different if the time component was part of a velocity calculation. As that has a well defined direction since it is a vector.

I agree Jeff, I was thinking of an example such as 20s-5s=15s.
To subtract the 2 journey times is pointless.
My fault, I'd forgotten where this strange topic had started from!

[guest39538]

Then maybe simply ^dt/_dt=0 net difference?

no, ^dt/_dt=1

for a difference you have to subtract eg t₁-t₂=δt

In my scenario

t₁-t₂=o

You can't simply subtract t2 from t1. Both of the time intervals are in the same direction since time does not go backwards. You gain nothing from the operation. It would be different if the time component was part of a velocity calculation. As that has a well defined direction since it is a vector.

its a net difference calculation of two journeys I need. two directions, the same speed and distance.