Special Relativity - apparent speed

In summary, the conversation discusses the concept of relative velocity in special relativity. It begins with a scenario where someone at rest is approached by a spaceship traveling at 0.8c. The question is asked about the speed at which the person sees the spaceship approaching. The conversation then delves into the idea of an observer's interpretation of velocity in special relativity and offers different scenarios to clarify the concept. The conversation concludes with an offer for further discussion and learning in the future.
  • #1
eprparadox
138
2

Homework Statement



I'm at rest. Someone in a spaceship is approaching me at a speed of 0.8c.

What speed do I see this person approaching me?
 
Last edited:
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  • #2
What do you think the answer is? Do you have any formulas?

Also, consider the scenario where you are traveling toward the spaceship with a speed of 0.8c as well. Since you are traveling at constant velocity, you can claim that you are at rest. What speed is the spaceship approaching toward you now?
 
  • #3
eprparadox said:

Homework Statement



I'm at rest. Someone in a spaceship is approaching me at a speed of 0.8c.

What speed do I see this person approaching me?

You said "someone is approaching me at 0.8c". Then you asked "what speed do I see this person approaching me"? That doesn't even need relativity in any sense. They are the same question.
 
  • #4
Dick said:
You said "someone is approaching me at 0.8c". Then you asked "what speed do I see this person approaching me"? That doesn't even need relativity in any sense. They are the same question.

Let's make him think a little bit. =)
 
  • #5
buffordboy23 said:
Let's make him think a little bit. =)

If you think that's useful, ok. Geez. eprparadox? I think formulas are useless here.
 
  • #6
I apologize to all who viewed this thread! There was more to this question and I phrased it incorrectly from the beginning anyways. I also had included formulas and an attempt to solve the problem, but for some reason it wasn't posted. I think I may have accidentally selected a portion of the text and deleted it before confirming the thread.

I'm an idiot, for sure. But not THAT big of an idiot!

But thanks anyways for the responses. That's awful kind of you guys.
 
  • #7
Do you understand how an observer interprets velocity using special relativity? Based on your question (at least the part that is given), it seems you need help and I wanted to offer a few scenarios to make things clearer.
 
  • #8
Hello!

First, thank you so much for your following up to my last post. I definitely do need help with this material. And it speaks volumes about the type of person you are that you would take the time to have a dialogue with me.

Now with that in mind, I think it would be best for me to first grapple some more with this subject. At this point, my questions would be superficial at best. I don't think I've given myself the best chance to learn the material and I think sometimes I'm too quick to post a question on this forum because I know I'll get a response. But once I've gotten to a certain point where I feel more comfortable, I would love to hear your explanations and ideas. I hope your offer will still stand in a few weeks.

Thank you again very much. I hope to speak with you soon.
 

FAQ: Special Relativity - apparent speed

What is Special Relativity?

Special Relativity is a theory developed by Albert Einstein in 1905 that explains the relationship between space and time in the absence of gravity. It states that the laws of physics are the same for all inertial observers, regardless of their relative motion.

What is the apparent speed in Special Relativity?

The apparent speed in Special Relativity refers to the perceived speed of an object in motion relative to an observer. It takes into account the effects of time dilation and length contraction, which can make the apparent speed of an object different from its actual speed.

How is apparent speed calculated in Special Relativity?

The apparent speed is calculated using the formula: v' = (v + u) / (1 + (v*u)/c^2), where v is the actual speed of the object, u is the speed of the observer, and c is the speed of light. This formula takes into account the effects of time dilation and length contraction.

What is the difference between apparent speed and actual speed in Special Relativity?

The difference between apparent speed and actual speed in Special Relativity is that apparent speed takes into account the effects of time dilation and length contraction, while actual speed does not. This means that the apparent speed of an object can be different from its actual speed, depending on the relative motion between the object and the observer.

Can apparent speed exceed the speed of light in Special Relativity?

No, according to Special Relativity, the speed of light is the maximum speed that any object can travel. This means that the apparent speed of an object cannot exceed the speed of light, even if its actual speed is greater than the speed of light. This is one of the fundamental principles of Special Relativity.

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