Relativity of 2 cars' velocities

In summary, the cars can always see each other, and the surrounding landscape would look the same to either car. The other car would appear to be moving backwards if it were measured on the ship.
  • #1
kyle1320
13
0
Suppose 2 cars are on a highway going toward each other, each at half the speed of light. Can the driver of one car see the other car as it is going towards him, past him, and away from him? I imagine as the other car was coming towards him, it would get blue shifted out of the visible spectrum, and oppositely as the other car was going away it would get red shifted out of the visible spectrum. But as they passed each other, would the other car appear to be right next to him, and stay that way? Or would he only see the other car for the exact moment they were next to each other? Would he never see the other car? Thanks in advance :)
 
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  • #3
-REMOVED- weird. I only took general physics, didn't even know about that. I just still have a lot of questions from that class. :P
 
  • #4
Sorry for the double post, but:

s = v+u / 1+(vu/c^2)

s = actual velocity of fly (car 1)
v = actual velocity of ship (car 2)
u = velocity of fly (car 1) as calculated on ship (car 2)
c = speed of light

so:

.5 = .5+u / 1+(.5u/1^2)
.5 = .5+u / 1+.5u
u = 0

So to each other, the cars would appear to be not moving. Is this what you meant by they would always see each other? What would the surrounding landscape look like then? Would the other car appear to be moving backwards?
 
  • #5
no, u and v are the actual speeds of the two cars, = 0.5,

so their relative speed = (0.5 + 0.5)/(1 + 0.5*0.5) = 1/(5/4) = 4/5 :wink:
 
  • #6
"As Galileo observed, if a ship is moving relative to the shore at velocity v, and a fly is moving with velocity u as measured on the ship"
"where s is the velocity of the fly relative to the shore."
 
  • #7
Galileo's ship is your highway :wink:
 
  • #8
As tt points out, the cars observe each other moving toward them at 4/5c.

I'm not sure what your Galileo reference is intended to portray.
 
  • #9
follow the link, dave! :wink:
 
  • #10
The ship and the fly are the cars, and the highway is the shore, as it is a stationary point of reference as to the velocity of the 2 cars.
 
  • #11
The OP made specific reference to the effects of redshift and blue shift of the light on the visibility of the cars, I don't think this was a question about velocity addition but rather about the extent of frequency shifting moving things out of the visible spectrum.

Light that is outside the visible spectrum is simply light that your eye does not register. The fact that the light bouncing off of a car is undetectable to your eye will not make the car invisible since you still will not be able to see the light from what is behind the car, since the car is in the way. Your eye simply will not detect the light reflected off of the car. Light not detected looks just like no light, which looks black. So if a red car is approaching at a high enough speed it will look blue, If there is a blue car right beside it approaching you at the same speed it will look black. As the 2 cars pass you the blue one will shift to red and the red one will shift to black.
 
  • #12
tiny-tim said:
follow the link, dave! :wink:

Yeah yeah. Quoting without context is meaningless.
 
  • #13
hi kyle1320! :smile:

(just got up :zzz: …)
kyle1320 said:
The ship and the fly are the cars, and the highway is the shore, as it is a stationary point of reference as to the velocity of the 2 cars.

but the shore (in http://en.wikipedia.org/wiki/Velocity-addition_formula" ) is not the stationary point of reference as to the given velocity v of the fly :wink:
 
Last edited by a moderator:

1. What is the definition of "relativity of 2 cars' velocities"?

The relativity of 2 cars' velocities refers to the concept that the velocity of one car can only be measured relative to the velocity of another car that is moving in a different direction. This means that the velocity of a car will vary depending on the frame of reference it is being measured from.

2. How does the relativity of 2 cars' velocities apply to real-world situations?

The relativity of 2 cars' velocities is a fundamental principle in physics and applies to all objects that are in motion. It is particularly important in situations where there are multiple moving objects, such as in traffic or on a racetrack, where the relative velocities of cars must be taken into account for safe and efficient navigation.

3. What is the difference between relative velocity and absolute velocity?

Relative velocity is the velocity of an object in relation to another object, while absolute velocity is the velocity of an object in relation to a fixed point or frame of reference. In the case of two cars, their relative velocity is the difference between their individual velocities, while their absolute velocities will depend on the frame of reference they are being measured from.

4. How does the relativity of 2 cars' velocities relate to Einstein's theory of relativity?

The relativity of 2 cars' velocities is a simplified version of the principles outlined in Einstein's theory of relativity. This theory states that the laws of physics are the same for all observers, regardless of their relative motion. In the case of two cars, this means that their velocities will appear different to different observers, but the laws governing their motion will remain the same.

5. Can the relativity of 2 cars' velocities be applied to objects other than cars?

Yes, the relativity of 2 cars' velocities can be applied to any objects that are moving in relation to one another. This includes not only cars, but also planes, trains, and even subatomic particles. The principles of relativity are fundamental to our understanding of the physical world and are used in a wide range of scientific fields.

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