No, not 20 m/s. For them, the ball moves at a speed of 30 m/s (i.e. 10 + 20). So much for common sense. The difference is due to the fact that they measure from different “reference frames”, one moving, the other stationary.
However, everything is fine; Everyone agrees to the result. If the ball hits the person, the villains and the observer would calculate the same influence time. Yes, people in the car see a ball moving at a slower speed, but they also see the observer approaching them (from their perspective), so in the end the same works.
This is the second main postulate of special relativity: physics is the same for all reference frames for specific, for all “inertia” or unvaccinating frames. Observers can move at different speeds, but these speeds must be constant.
In any case, maybe now you can understand why it is really quite strange that the speed of featherlight is the same for all observers, regardless of their movement.
Waves in an empty sea
How did Einstein receive this crazy idea? I will show you two reasons. First, the featherlight is an electromagnetic wave. Physicists have long known that the featherlight survived like a wave. But the waves need mediocre “Brew”. Ocean waves require water; Sound waves require air. Remove the medium and there is no wave.
But then, what medium did sunlight go when he traveled in space? In 1800, many physicists believed that there must be a medium in space and they called it Luminifer etteter Because it’s nice to say.
In 1887, Albert Michelson and Edward Morley developed a clever experiment to detect this ether. They built a device called an interferometer, which divided the beam of featherlight in half, and sent halves along two paths of an even length, jumping from the mirrors and re -connecting in the detector, yes:
Illustration: Rhett Allain