Slow Sock on Lubricon VI
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Slow Sock on Lubricon VI : What would happen to a slowly moving frozen sock on a frictionless planet
- This is a picture of the planet : Lubricon VI
- And Lubricon VI is a very special planet,
- Because it's made of a yet to be discovered element called Lubrica
- And Lubrica is special because if anything glides across the surface if Lubrica
- It will experience absolutely no friction.
- So if this right over here if a sheet of Lubrica
- We're looking at it from the side.
- And if we have a brick on top of it,
- maybe gliding on top of it, like that,
- it experiences absolutely, it experiences absolutely no friction.
- Now the other things we know about Lubricon VI,
- it's drifting in deep space,
- and it does not have an atmosphere.
- In fact, it is a complete vacuum outside
- It's in such deep space,
- such a remote part of space
- that there aren't even a few hydrogen atoms.
- right over here,
- is a complete, absolute vacuum.
- And it's also an ancient planet.
- The star that it used to orbit around
- has long since died away.
- So it's just this lonely planet drifting in deep space,
- without an atmosphere.
- The other thing we know about Lubricon VI,
- is that it is a perfect sphere.
- it is a perfect sphere..
- Now my question to you, for some bizarre reason,
- There happens to be, on the surface of Lubricon VI,
- so this right over here is the surface of Lubricon VI
- There happens to be a sock that is frozen in a block of ice.
- So this is my sock, and it's frozen
- It's frozen in this block of ice.
- And it happens to be travelling at 1 km/h.
- in that direction.
- If we look at it in that macro scale,
- When we were looking at that planet,
- Let's say that that is the frozen sock,
- and it is traveling along the equator.
- It is traveling along the equator of Lubricon, of Lubricon VI.
- So my question to you, given all of these assumptions we made,
- that it has absolutely no atmosphere
- It's a perfect sphere,
- and Lubrica has absolutely no friction
- regardless of what's traveling on top of it.
- What will happen to this rock,
- or, or I should say..
- to this frozen sock over time?
- To answer that question, we need to
- think about all of the forces
- that are acting on this frozen block of
- I guess, this frozen block of ice and sock.
- And first of all, let's think about
- the forces that are acting in the radial direction,
- inward or outward of the center of the planet.
- Well, this planet has a mass,
- and so you have a inward force
- towards the planet's center of mass.
- And so you have the force of gravity acting on this block,
- going radially inward to the center of the planet.
- So I'll draw it like this,
- So we have our force of gravity.
- It's going radially inward, just like that.
- But then we know that the block is
- not just biraling towards the center of the earth,
- We have the surface here.
- It's not going to go through this surface of Lubrica.
- We can also assume that Lubrica is a very, very. strong material.
- So you also have a normal force
- that is keeping the block from spiraling towards the center of the earth.
- So this is a normal force.
- And one thing I will think about now,
- and will adress directly in another tutorial,
- is whether this normal force is equal to the
- is equal to the force of gravity.
- We'll think about that in a future video.
- But these are all the forces that are acting
- in the radial direction.
- either inward(towards the center of the planet)
- or outward.
- But if we think about the tangential direction,
- along the surface of the planet,
- there are no net forces.
- And because there are no net forces,
- in this tangential direction, right over here,
- this block will not either accelerate, nor decelerate.
- There is no air friction, there is no friction,
- or I should say air resistance,
- which is really the friction with the particles
- if you had an atmosphere,
- It's a complete vacuum, so there's nothing there.
- There is no friction with the surface of the planet.
- So there's no friction there,
- which could have been a force in the tangential direction.
- So there's absolutely no forces in the tangential direction.
- So this block of ice will
- actually continue to travel at 1km/h
- for all of eternity.
- So it'll just continue to do it
- given the assumptions that we just made.