The error bars are calculated using the crank three times method from the standard deviation in angle measurements. View Iframe URL.
What's going on here? Let's look at the data for the teflon the blue data. I fit a linear function to the first 4 data points and you can see it is very linear. The slope of this line gives a coefficient of static friction with a value of 0. However, as I add more and more mass to the friction box, the normal force keeps increasing but the friction force doesn't increase as much.
The same thing happens for friction box with felt on the bottom. This shows that the "standard" friction model is just that - a model. Models were meant to be broken. Really, what is friction? You could say that when two surfaces come near each other call them surface A and surface B , the atoms in surface B get close enough to interact with surface A.
The more atoms that are interacting in the two surfaces, the greater the total frictional force. How do you get more atoms to interact from the two surfaces? Well, if you push the surfaces together you can get more atoms from A to be close enough to the atoms from B to interact. Yes, I am simplifying this a bit.
However, the point is that contact area does indeed matter. I am talking about contact area, not surface area. Suppose you put a rubber ball on a glass plate. As you push down on the rubber ball, it will deform such that more of the ball will come in "contact" with the glass.
Here is a diagram of this. Unlike ships in water, a ship in space does not need constant thrust to keep moving forward. The astronauts on board the International Space Station are accelerating towards the center of the Earth at 8. Yes, when two surfaces rub together in outer space, there will be friction. Indeed, as you realise, there is no friction in space.. But this dust will not cause any significant drag unless you move really fast relative to the dust say, at a significant fraction of the speed….
In a hard vacuum, there is nothing to cause any friction. That said, the ISS is actually low enough that it still experiences atmospheric friction. Not much, just enough that it needs to fire its thrusters every few years. Night vision goggles prove that any warm body emits infrared light, but even frigid intergalactic space is awash in microwave photons that would gradually slow a drifting space traveler. The friction occurs because the moving object absorbs more photons at its front surface than at its rear.
The object slows from the flow of photons, just as a cyclist is slowed by the wind she feels in her face. After establishing the mechanism, the team worked out exactly how long it would take various materials to slow down in different situations. A metal would feel a stronger drag than a nonmetal, Podgornik and his colleagues found, because metals can absorb light at all frequencies, unlike nonmetals. In intergalactic space, the slowing of a macroscopic object would only be noticeable over billions of years.
Their setup, described in a paper to appear in Physical Review A , uses nanometre-wide silver rods stuck in a substrate like candles on a cake. So if a perforated metal bar was lowered over the candles, with a candle poking through each hole, the bar should float, repelled in all directions by the candles between and around each hole. How to float above a vacuum Houdini would be proud.
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