2020-07-15

# A 300,000-kilometer stick rotates around a fixed point, and one second per second. Can the end of the stick exceed the speed of light?

Because the speed of light cannot exceed the theory, I believe that many people must be dissatisfied. Imagine that if you rotate one end of a 300,000-kilometer iron rod along a fixed point, it only needs to rotate for 1 week per second, regardless of the broken rod. According to other factors, according to the calculation of the circumferential length formula L=2πr, does the linear velocity at the end of the stick reach 1.884 million kilometers per second, which is 6.28 times the speed of vacuum light. If the object speed can really reach 6.28 times the speed of light, it must be Exciting, continue to calculate according to this idea, as long as the length of the object is long enough and infinitely long, such as 1 light year long, as long as one end makes a circle along a point, no matter how slow the angular velocity is, the linear velocity at the end will exceed the speed of vacuum light. In this way, it is too simple to exceed the speed of light.

Is this really the case? When you know two physics knowledge, you will definitely not think so again, because in practice, it is never possible, the first knowledge is the speed of force propagation in the object, and the second knowledge point is proposed by Einstein The speed of light cannot exceed theory.

Speed ​​of force propagation

Although daily life experience tells us that when one end of a long stick is pulled forward, the end of the stick will also move forward simultaneously , But from a scientific point of view, the moving speeds of the two ends are not synchronized. This is because the force takes time to propagate from one end of the stick to the other end, but the propagation time is very short, and we simply cannot perceive it, which makes us mistaken for the stick. Both ends are synchronized.

So how fast does the force propagate in an object? The experimental results show that in objects, the force and sound propagation speed are the same, and in different substances, the force propagation speed will also be very different. For example, in the wooden stick and the iron rod, the distance of the force propagation speed is extremely large. In the wooden stick, the force The propagation speed is only 500 meters per second, but in the iron bar, the force propagation speed is about 5000 meters per second, which is a full 9 times faster.

If you don’t consider other factors, the end of a 5000-meter long wooden stick will be moved after 10 seconds, and the end of a 5000-meter long wooden stick will be moved. The end just moved in 1 second. If the length of the stick is shorter than 2 meters, no matter whether it is an iron stick or a wooden stick, the force propagation time is extremely short, and no one can feel it. One end of a 300,000-kilometer long iron bar is done along a fixed point In a circular motion, at a speed of 5000 meters per second, the time to force to the end takes 60,000 seconds, which is approximately equal to 16.66 hours, which means that when we move the end of the iron bar hard, the end will only move after 16.66 hours.

The speed of light cannot be exceeded

The speed of force propagation in an object can only indicate that each part of the object is not synchronized, but it still does not indicate that the object will never The principle of speed of light will be exceeded, but in 1905, Einstein proposed the theory that the speed of light cannot exceed, that is to say, no matter how you assume, in fact, the speed of motion of all objects cannot exceed the speed of light. In the large hadron collider, regardless of the particle No matter how much energy is applied, their flight speed can never exceed the speed of light, at most it is close to the speed of light. Many scientific experiments have proved the fact that there is no way to surpass. At present, no object can be faster than the speed of light in vacuum. No matter how hard scientists try, the speed can only be close to the speed of light, but there is no way to surpass it.

The speed of light seems to be the upper limit of all speeds, just like the absolute zero degree of 273.15 degrees Celsius, there is no lower temperature than this. Therefore, when a huge iron rod with a length of 300,000 kilometers is moving in a circular motion, no matter how much force you exert on one end, the linear velocity on the other end cannot exceed the speed of light, at most it is close to the speed of light. Is limited. Besides, in reality, a huge iron rod with a length of 300,000 kilometers There are other issues to consider, such as deformation and attenuation of force transmission, so no matter what we do, it is in vain. The speed of an object cannot exceed the speed of light. Perhaps the speed of light will be the ultimate speed of the universe. For interesting scientific exploration content, please pay attention to the only WeChat public account:interesting exploration