Movements, inertia, etc.

1999/04/01 Bandres Unanue, Luis Iturria: Elhuyar aldizkaria

• Fisika

Starting from the train

If we ask anyone if when we jump from the train we look forward, that is, towards the direction of the train or backwards, surely, this will tell us "according to the law of inertia, looking forward". But deepening a little more, if you are asked what relationship this has with the law of inertia or how it indicates, surely you will begin to speak to leave your idea totally clean, but if we do not cut it, when we reach a point we remain mute: according to the law of inertia… the jump should be retrospective, that is, it will deduct the sense of the train and not as you said at the beginning.

In the above case, the law of inertia has only a secondary role, since the main reason is the other. Of course, if we ignore all that is true reason and focus only on the law of inertia, we will come to the wrong conclusion, if we want to put into practice what the theory has then said with its regrettable result.

Let's think we have to jump down the train that is going your way. What will happen?The inertia of the jump from the train makes our body have the same speed as the train with the ground and the tendency to move forward. But the jump against the march of the train, that is, back, and if we make it strong, at the speed we have with inertia is removed the setback that we do with the jump and, therefore, the speed with the earth will be less than in the first case. The risk of falling to the ground will not be so much.

However, when we jump out of the vehicle we all look forward (though our body is moving). Without a doubt, this is the right way and we warmly recommend our reader.

But how can that be? Because the above statement is not correct or complete. The reason we have to fall after making the jump looking anywhere is that, while the upper part of our body wants to keep moving according to the train, the feet tend to stay when touching the ground. But if we jump forward, as we usually do, we will have the opportunity to take a few steps and avoid falling. These types of activities are what we do daily when we walk. Walking, from the physical point of view, is nothing more than a lot of bushes forward: we avoid the real fall because we advance the necessary leg.

However, if we pulled ourselves from the train looking back, despite having a more logical view of inertia, we would not have the opportunity to take steps and fall. On the other hand, it is always more appropriate to fall forward and somehow soften the consequences of the blow with hands.

From this we will come a clear conclusion: that the greater security of the leap forward corresponds more to our ability to advance than to inertia. Therefore, this rule is not met with objects. If we are going to throw a fragile object from the train, such as the bottle, it is better to pull it back than forward, as the probability of breakage will be lower. Therefore, knowing that the best way to get out of the train is to be still, if at some point you must leave the one that is going, first throw your bags or luggage and then look forward (and with push back). Thus, on the one hand, due to inertia, you will reduce the speed of the body and, on the other, you will avoid the risk of falling upside down.

Grab the shot with your hand

According to news in a newspaper during World War I, a French aviator had something strange. While traveling on a plane two kilometers from Earth, he realized that he was moving a small object next to his face. Thinking he was going to be a bug, he surprised him with his hand. And… look, he was surprised to see that what was caught was the bullet of a German rifle.

This brings to mind the tales of the Baron of Münchhausen, who said that this baron grabbed a cannon shot. But apart from the stories, the news is not at all impossible.

The bullets do not always go with their initial speed, that is, with an approximate speed of one thousand meters per second, but because of the resistance of the air they go slower and only have a speed of forty meters per second before falling. This speed was possible for the planes of the time, so, despite the chance, bullets and planes could have a similar instant speed and then the bullet would be practically stagnant compared to the aviator. Therefore, this could be easily caught by hand; with the glove, of course, the bullets are heated a lot by friction with the air.

Bird risk

If in suitable conditions the shot is transformed into something not dangerous, we can also have the opposite, that is, the low speed of the "peaceful body" can cause negative effects.

Due to the huge speeds that jet aircraft have reached in recent years, in some cases there have been breakdowns (and in some cases accidents) due to collision between aircraft and birds. Someone may wonder what danger a light bird can pose for a plane with more than one hundred passengers? But when the bird hits a plane at a speed of five hundred meters per second, it can break the metallic coating or glass of the pilot's cabin. And what will we say if it somehow enters the engine hopper? As a result of this clash, about twenty-five years ago, American aviator Theodore Erymann died during a training flight on a jet plane.