Take a stationary (fuzzy) electron, and zoom past it at some speed $v$. In the electron's frame it is at rest and you are zooming past at $v$, but in your frame you are at rest and the electron is moving at $-v$.
why isn't a useful question. Quantum objects are fundamentally different from what we think of as classical objects. They are always spread out (delocalised is the technical term) so they do not have a single position.
When you say why do books write it that way I assume you're thinking about the Bohr model.
The Bohr model is wrong, and I don't know why it's still taught. It just confuses students.
Students often try to approach QM by starting with a classical approach and trying to see what changes when you move to QM, but this is not a good way to do it. QM is fundamentally different from classical mechanics.
This is what the eyepiece of the telescope does. The lens at the far end creates an image of the object you are looking at, and the eyepiece then magnifies that image just like holding a magnifying glass up to your eye.
You want the eyepiece to have a high magnification, i.e. like a powerful magnifying glass, so you want it to have a short focal langth. Yes?
@yuvrajsingh The objective lens creates a real image inside the telescope, then the eyepiece creates a virtual image of the real image. Finally your eye creates a real image of the virtual image on your retina.
With Vernier scales you very quickly get to understand them intuitively, so at a glance I can see the upper scale is 2.87 and the lower 2.83. But until you get used to them I can show you how I would approach them. This does not necessarily match what your book will say. Shall I go ahead and say how I would do it?
The two scales match where I have drawn the red line. This is at 7 on the Vernier scale and 35mm on the main scale. (I've just realised I mislabelled it as 3.5mm - sorry)
So suppose we start at the red line, i.e. at 3.5cm, and move backwards to the zero on the Vernier scale. That is, we move back the distance shown by the blue arrow. This takes us to the reading.
Actually there isn't a simple way to tell because it depends on how the gauge has been designed. With a real gauge you just turn the screw one complete turn and see how much it moves along the main scale.
In questions the question will normally tell you what the main scale division is.
@yuvrajsingh the gauge is designed so that the screw shows zero when it is exactly lined up with a main division. So when the main gauge was at exactly 0.55cm the screw gauge would have shown zero.
So the question is how far past zero have we turned the screw gauge.
And looking at the scale on the screw gauge it reads 12. Yes?
And we we know one complete rotation of the screw gauge moves 0.05cm on the main gauge. So 12/50 of a rotation moves a distance $x$ along the main gauge where $x = 0.05cm \times 12/50$. Yes?
@JohnRennie I read somewhere, just now, that Black Marlins secrete an oil-like substance from a special gland on its skin. It is suspected that this oil might have reduced the drag when it swims. I don't really find this intuitive or at least right now. I mean I know why oil makes the floor slippery, but what about sea water? Aren't they both liquids, in a sense that the water molecules could already move 'freely' , so how does oil play a role here?
@yuvrajsingh you can use a screw gauge to measure anything you want.
@KevinN I would guess the oil just smoothes out the skin.
The fish skin is probably slightly rough due to irregularities on the scales. If the oil is thick and gooey it will spread out to form a smooth film and help remove the irregularities.
When you have a lot of bumps in an object, and is moving through water, how exactly does that increase drag. I would suspect that it increases the surface area and more water molecules would start 'bumping' ?
@KevinN Well if you replace the crappy old mechanical disk by an SSD and bump the RAM to 8GB that will be a nice fast laptop. Both of those you can o yourself in 15 minutes.
One issue, again, is that my monitor breaking down, there's a black line across the screen. I mean you get used to it, but it would be a pleasure to my eyes to see that removed.
There has been a lot of criticism of Stadia, but mostly because of the terrible way Google rolled it out. If you can get Stadia working then it appears to be pretty good.
@KevinN I wouldn't try and play it over a mobile link. You need a fibre link eally.
Other companies will be releasing competing services in the next year, so even if Stadia bombs one of the others should make it.
