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Because atoms are not infinitely small. The fact that we don't see infinite gravitational forces between two touching objects actually tells us some interesting things about the nature of ordinary matter. As Stan Liou's answer quite correctly points out, for spherically symmetric masses the gravitational attraction depends entirely on their masses and on ...

12

The inverse-square law holds for spherically symmetric objects, but in that case the main problem is that $r$ is the distance between their centers. So "very close" spheres are still quite a bit apart--$r$ would be at least the sum of their radii. For two spheres of equal density and size just touching each other, the magnitude of the gravitational force ...

1

The gravitational constant is extremely small (approximately 6.674 x 10^-11 N (m/kg)^2). So, even though no force can be seen in your example, it still exists. The force could not go to infinity since the force is measured from the center of mass, not the surfaces.

1

I'm not sure what kind of steel you are using, but with stainless steel, many varieties are slightly magnetic. As I recall, when we were building a spectrometer that was very sensitive to magnetic fields, we were careful to use only "austentic stainless steel", which is not magnetic. I think that we paid extra for this feature :) ...

5

If you try jumping on a trampoline, you will notice that when you jump up, the trampoline bends and stretches underneath you. It stretches some even if you stand still, but it stretches extra when you jump. The trampoline is elastic. When it's stretched, you can feel it pulling back towards its normal shape. Thus, just before you jumped, the trampoline was ...

4

No, it has nothing to do with sound quality. In fact, the grid or covering is carefully chosen to interfere with the sound as little is possible. Speaker cones must be light weight, so are made from paper or other thin and delicate material. The grill is to physically protect the delicate speaker cone from getting dinged, a curious cat, or some moron with ...

2

Frankly, until you bring along an accelerometer as well as tracking the bus's speed thru corners (I'm assuming you mean you sway during a turn, not just going down the road), I'm going to remain skeptical of your claim. Centripetal force is centripetal force. Now, if you happen to counteract turning force unconsciously, it may be that you feel more ...

0

You should be able to do it by jumping off a table onto a spring scale. Simply film the jump with a high speed camera and look for the shockwave that moves through your body as you are landing and note when it reaches your neck. At the same time note the distance the spring has moved (call it point x). Then note how much further the spring moved afterwards ...

0

Let's quickly quantify Skliv's and Alfred's answers. The neatest way to do this is to consider the part of the cable bounded at its lowest point on one side and a general point on the other with the $x$ axis in the plane of the curve and pointing horizontal: The crucial assumption here, expressed in various ways in the other answers, is that the rope is ...

2

I heard a few times that using them as sunglasses is hurting the eye since UV light is not filtered, but the pupil is wider than it would be w/o wearing them because the visible light is dimmed. IFAIK, there is no evidence for this claim. See this paper (unfortunately, it's behind a paywall): The supposition that, because of pupil dilation, there ...

5

Movies don't get away with 24 frames per second. In old 35mm film movies, 24 new frames are shown every second, but each frame is actually flashed onto the screen twice. The flicker is therefore at 48 Hz, even though the data update rate is 24 Hz.

4

Creating a vacuum above carbonated drinks causes the CO2 to outgas faster--simply because there is no CO2 above the drink to diffuse back into the liquid. In physical terms this means there is no vapor pressure of CO2 above the liquid, so net movement of CO2 is from the drink to the space above it. If you leave a closed carbonated drink bottle long enough, ...

1

You can use planetarium software to locate Milky Way precisely. Generally, if you want to observe Milky Way center, which is in Sagittarius constellation, you should exclude the time, where the Sun is there (at that time Sagittarius is up in daytime and not visible). This occurs in December-January and does not depend on geographic location. All close ...

3

You need three things to get a great view on the Milky Way: 1) no bright lights (no sun in view, no moon in view, and no other lights blinding you), 2) no objects obstructing your view on the sky (no tall buildings, no trees, no clouds), and 3) your patch of earth oriented such that the Milky Way core is roughly positioned above you. Earth makes its annual ...

1

This is an interesting observation and I reckon it just shows that there's a difference between physical work and what we subjectively consider as work. Of course, you assume that the force field is conservative, neglecting any friction, but even when we take friction into account, it does not solve the mystery. I find the example of the bicycle driver ...

5

Ascending a hill diagonally means that while the work is the same, the power expenditure is lower (but it takes longer), which is why it is easier.

0

As the hot air goes up and the cold air goes down, the radiator is located where there is a better circulation, ie, even though the window is double glazed, there will always be cold air entering the division by the material itself. So the cold will push the hot air inside the room. Another explanation can be the fact that external walls can have thermal ...

1

Because under window is the place where delta-T (the Change in Temperature) is largest in the whole room. The larger is delta-T, more efficient the system is. Window even when closed is still a coldest place, because it is a thinnest wall. Cold air flows downwards, thus under window. What is an efficiency of a radiator depends on whether your goal is to ...

-1

Its because the hot air that is created by the radiator heats the colder window making the glass warmer... therefore the glass is allot less likely to condensate and at the same time keeps the room allot warmer because the heat will radiate out wards away from the window along with any drafts or such ... also if the radiator is placed on a wall without a ...

1

Reason is quite simple. If you have a window without radiator and outside is really cold, the window glass would be cold as well. This will lower temperature of the air around the window and this air will flow immediately down (physics). So if someone want well heated room with very cold floor .. do it, put radiator to opposite side. That's why it is wise ...

0

A number of reason: - the wall under the window is basically useless - placing the heater under the window allows you have a more even temperature throughout the room: the window is the coldest place in the room, if you were to place a heater on the other side of the room and wanted to reach a certain temperature by the window, the other part of the room ...

3

As the hot air goes up and the cold air goes down, the radiator is located where there is a better circulation, i.e. even though the window is double glazed, there will always be cold air entering the division by the material itself. So the cold will push the hot air inside the room. Another explanation can be the fact that external walls can have thermal ...

38

Since this is a physics forum I assume the OP is interested in a quantitative answer in terms of the efficiency of the system and how it differs based on the relative positioning of heat sources and heat sinks. The math required to analyzed such a system is too much for me to manage right now, but I believe the following principles apply and are objectively ...

6

As described in the other answers, putting the radiators (or hot air vents in a forced-air system) under the windows offsets the greater heat loss of the windows, but there is another reason. As room air flows over the surface of a window, it will lose heat to the window (and the outside). This can cause moisture in the air to condense out onto the window. ...

7

As Programmer mentions, by putting the radiator in front of the area most prone to heat loss and ingress of cold air, you are effectively screening off the room from cold air. However, there is also the fact that radiators are often quite a bit hotter than other heat sources such as forced air. Therefore it makes sense to put it in the coldest part of the ...

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The reason is because the heat loss occurs mostly in the windows and the fenestration. The idea is that you would like the incoming air to be heated up. Also, it creates an air curtain that prevents more heat from being lost through this exposed areas. The final reason is to make the temperature of the room more or less uniform. If the heaters were placed at ...

1

My guess would be it's there to prevent the cooling air from accumulating below the window and flowing into the rest of the room. Anything goes to avoid cold feet ;)

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Partly practical, the wall under the windows isn't useful for anything else. We had a house where the heaters were placed in the middle of the only empty walls, so nowhere you could put furniture, bookcases, etc. Before double glazing there would be a draft from the windows so the idea was to heat this incoming air by having a radiator immediately below the ...

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