Levers are amazing!

today I want to shine light upon one of the simplest machines that there ever were. Those are levers, so intuitive that you will see even small kids use them.

SPOILER alert:

They are amazing in crushing your fingers.

I kind of connect this word with the game Neverwinter Nights where it was used for the handles on walls that opened doors and so on, I had to use translator to make sure it was right because it did not feel so.

With this “door thing” it could come up to your mind that levers are kind of long rods of wood or iron. It is quite useful to have them like that.

Take for example something very close, door handle is an amazing illustration of how levers should look like! It is long quite enough for you to open the door.. now try to take

Epic door handle

just the closest part to your door, the one perpendicular to the plane of door. Sure it is much harder, probably even impossible for you to open them. This is because the further away you are applying force from axis of rotation the easier it is to rotate the whole thing.

Lets assume you have one Czech locomotive of class 363.

V čele orient expresu.

This is old Czech locomotive… there is ENGLISH wiki page about it!

Lets say that you are able to stabilise it and you have unlimitely strong rod of something that is also weightless. Also you have something that works as axis of rotation and it is also undestructible.Levers are amazing!

Everything is put like above. Lets say that you weight 70 kilograms (if less than you have sack of sand with you, if more than you touch the ground with your feet).

How far away do you need to be if you were able to put the locomotive 1 centimeter from the axis?

Well, we have to calculate it precisely because if you sit too close you are going to be thrown across a long distance!

What you want for balance is that the final moment of force is equal to 0. Both you and the locomotive has this moment which means that:


You calculate the moment here pretty easily, there have to be to things in the equation and those are very intuitive. If you push on door handle very hard (force) it is easier. If the door handle is longer it is also easier (r for distance).


This type of locomotive weights 87 tons. Now we can calculate the moment (F=m*g):

M=87 000*10*0.01=8 700 N*m

You moment of force must be the same and you know your weight (times gravity acceleration) so there is last thing the distance.

r=8 700/700
r=12.4285714286 meters

Wow, only if you are 12.5 meters from the train you can easily rest down! The problem here is that usually in this type of physics we consider that all of mass of one object is compressed on one place called center of mass. This is the problem because in reality whole locomotive simply wont be 1 centimeter away from the center. Cool anyway 😉

I mentioned at the start that levers are good in crushing fingers.. and they are. Take for example door that is 0.8 meter long and somebody pushes it with the force of 5 Newtons which is like lifting 500 grams. If your finger is 2 centimeters from the door it is literary going to be crushed with the force of 200 N which is like putting 20 kilogram thing on your pinkie.



How to! 3) Sail against wind

if you have ever been on a sailing boat you know this one. How can you sail against wind without using paddles when the force will move you back? There is a way, and it is pretty neat!

Below you can see the picture of boat which is pushed by wind, but what if it wants to go up? There is way called: crossing.

How to! 3) Sail against wind

Below you can see how boat can move to up and left. Here the wind is shown by these brown arrows. Blue arrows are friction from water. The thing is that when the sail is like this, wind is trying to push it mostly to left. Have you ever tried to push boat from one of the sides? It is way harder then pushing it from front or back, this is because you need to push the great amount of water that is right behind the boat and also because of friction. So the boat has one more way to go and that is forward, amazing.How to! 3) Sail against wind2

If your destination is actually right against the wind you can do the same every once a while but on the other side so you are “crossing”, making your way longer but still effective.

Picture of how the sails must be turned so you can sail in desired direction, you can see that there is a direction in which you can not sail but by changing the direction you can achieve the same thing.


Tidal force

sorry for not writing such long time, I was enjoying holidays for whole week. Anyway I am coming back with post about tidal force.

Tidal force is effect of gravitational force and it can be seen as for example tide.

So you have Moon which is attracting everything, even water in our oceans. Water closest to Moon is attracted with greatest force while water far away with least. As you can see on the picture there is Moon (Satellite) on the right this grants us two high tides per day.
So as is Moon orbiting it changes the place where low and high tides are.

This effect creates amazing things: rings! Planetary rings can be made by some satellite which moved too close to its planet and tidal forces were so strong that it ripped it apart, so there is higher probability that larger planet will have ring.

Tidal force also can be “seen” in effect called spaghettification which is made by black holes or other massive objects.