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B Car Driving At A Constant Speed

  1. Apr 14, 2016 #1
    Hey guys,
    This might sound like a simple question, but I'm just starting to look in depth into Einstein's theories. I'm confused on the question about a car driving at a constant speed o 65 mph northwards. If it changes it direction to drive northeast, it then loses some speed. How is this possible if it is always driving at the same speed? Thanks!
  2. jcsd
  3. Apr 14, 2016 #2
    i think you have traveled in a car and must have taken turn keeping your speed constant - but driver slows down at the turn and speeds up again to maintain his speed/or
    there are signs at the turn-drive slowly bend ahead.
    so what is happening?
    and how this motion relates to Einstein?
  4. Apr 14, 2016 #3


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    It isn't. If it's moving at the same speed, it's moving at the same speed.

    Note that there is a difference between speed and velocity. Velocity is a vector whose magnitude is the speed - so velocity is speed in a direction. The velocity changes when the direction changes (in this case the component of velocity in the northward direction decreases), but the speed might not.

    Edit: if I misunderstood your question, I apologise, but if you aren't comfortable with vectors I think you are going to have some serious problems understanding relativity in depth. I'd suggest taking a look at a lower level physics and maths course or book first.
  5. Apr 14, 2016 #4
    It's all a matter of what you stipulate. If you stipulate that its speed is constant then it doesn't slow down, if you stipulate that it slows it slows. Is this about velocities and directions?
  6. Apr 14, 2016 #5
    Is this a frame of reference question?
  7. Apr 16, 2016 #6
    1) If I drove my car for half an hour at 65mph north, then I drove North/East at 65mph for half an hour, what distance would I have covered in an hour?

    2) If my mate drove his car at 65mph for an hour north, what distance would he have covered?
  8. Apr 16, 2016 #7
    So what exactly are you reading about Einstein? - I believe the point of the discussion is about relative to what point of observation.
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