84

The very first thing you should do is stop using your oven and have it checked out by an authorized repair service. If in fact the oven was operating with the door open, there was a failure of the door interlocks to turn the oven off and a failure of the backup system intended to permanently shut the oven off in the event the interlocks failed which, ...


77

Take a look at this picture of a cup slightly out-of-balance : In case (A), generated torque is directed out of your reference axis and in case (B) - towards your reference axis. So in case A), you need to compensate out of balance movement with your finger contra-movement. But in case B), torque assists you and makes balancing for yourself, so that you ...


65

If the air was still, body heat warms a thin layer of air next to the skin. This warm air would stay near the skin, separating it from the cold air. Wind, however, continuously blows away this warm bit of air, replacing it with the colder surrounding air. There's a similar effect on humidity. Evaporating sweat increases the humidity right next to the skin, ...


65

When you pour the hot water in, the air inside the thermos is still quite cold (ambient temperature, approx.) But then when you shake it up the cold air is heated by the hot liquid. Gases expand considerably when heated, approximately acc. the Ideal Gas Law: $$pV=nRT$$ This causes a modest (and harmless) pressure increase in the flask, which is what you ...


56

Yes. A simpler way to look at this is that because freezing, as well as resublimation (turning a gas directly into a solid) emits heat. It may seem strange but consider this: you need to put in heat to make water turn from solid into liquid, so the inverse process should transfer the heat in the opposite direction. And that's what it does. In cold air the ...


53

The human gait has a natural bobbing motion, with the head moving slightly up-and-down and side-to-side. The side-to-side motion (swinging on an axis parallel to the nose) turns the ponytail into a natural pendulum which swings back and forth, since this plane of motion is gravitationally symmetric and has nothing to stop the swing. Small driving forces can ...


51

There is another effect here which is significant, as follows. Warm water wants to evaporate, but in a flask-shaped container, the evaporation can take place only at the free surface of the water in the flask. Furthermore, as soon as the boundary layer of air right next to the warm water becomes saturated with vapor, the diffusion of water vapor into the air ...


50

The skateboard is able to lift off the ground because of the momentum imparted to it by the skateboarder pushing down on the kicktail. The skateboard acts as a lever around the rear wheels, so when the kicktail is pushed down, the center of mass of the skateboard rises up. If you do this fast enough, the skateboard's center of mass gets enough upward ...


49

A large amount of water (i.e. if the path of light through it is long) will simply start absorbing light, as it's not completely transparent. For smaller amounts, as when pouring it from one container to another, this is mostly negligible. However, there is also surface reflection. A small amount of the incident light will be reflected off by the surface. ...


47

This is just to add an illustration to noah's and Ralf Kleberhoff's answers which correctly point out that refraction is the main reason. Note that although most of the light rays do make it through the water drop, most of them do not continue on the path with the rest of the light bundle, but end up somewhere else. As a result, right behind the drop, the ...


46

Note that double-wall plastic cups aren't strong enough to withstand a vacuum and so they usually just contain a thin layer of air in which convection currents (absent in the case of the vacuum) can easily get started. This will bleed the heat out of the contents of the cup much faster than in the vacuum case.


44

The magnetron injects microwave radiation at a certain rate. Ignoring losses, that radiation bounces around the walls until it’s absorbed by the food. If you put two burritos in there instead of one, on average there will be fewer bounces before absorption. That means that with two burritos, the average intensity of the radiation impinging on any point is ...


41

Colour can come from pigment particles embedded in the translucent rubber matrix absorbing light. When you pull the band the particles become separated by a longer distance, but being themselves inelastic remain the same size. Hence the amount of absorption per unit area decreases, and the band become lighter in color. Simulated rubber band with pigment ...


41

Your body’s circulatory system is removing heat from your hand inside the oven mitt. This makes your whole body act as a radiator to dissipate the slight temperature increase in your hand and keep the temperature from rising too much inside the mitt. The mitt acts as an insulator and slows the heat transfer into your hand to a rate that can be radiated by ...


41

Popcorn pops in a microwave oven due to the microwaves interacting with the moisture in the popcorn kernel raising its internal temperature and pressure. Once the pressure increases enough the kernel pops and the moisture escapes and cools. The moisture in the un popped kernel remains hot. Hope this helps.


39

Combustion is... complicated. Essentially what is going on in flame is that you have molecules of fuel and oxidizer that mix and start to bounce off each other. If the molecules are moving fast enough (meaning they have enough energy, which we measure as temperature), then when they collide with each other, they start to make the fuel and oxidizer fall apart ...


39

Mist is a suspension of tiny water droplets in air. Light traveling through the mist gets randomly scattered, mainly by bouncing of the droplets. That makes mist far less transparent than bulk water. I don't think mist is literally gray in colour but the fact that mist is far less transparent than pure air (or bulk water) causes it to look the way it does. ...


37

Although there are already some good answers, I'd like to give it another attempt. Water is transparent in the sense that most of the light that enters some volume of water, also exits at the other end (unless we talk about multiple meters of thickness or lots of dirt in the water). But that doesn't mean that it passes water unchanged. Wherever light enters ...


36

There is a reason steel is better for thermos flasks than plastic: lower emissivity. The way a thermos flask works is that it has two walls ideally separated by vacuum. Heat passes between them as blackbody radiation, with each unit of area transmitting $\sigma \epsilon T^4$ watt per square meter. Here $\epsilon$ is the emissivity, which for polished steel ...


35

Rubber bands are made of polymers (more specifically elastomers). A given polymer in the band can either be aligned with other polymers around it, or it can be misaligned. Therefore, you can end up with regions of order and regions of disorder in the band. In an unstretched band you have much more disorder, but when you stretch the rubber band you are ...


33

Updated Answer based on comments by @ToddWilcox that actually know more than me about this. The answer by @NuclearWang is correct, but I wanted to illustrate the process a bit. At least the initial part that sets things up for the stunt. Stage I At this stage, the foot pushes downwards, but the reaction from the ground is greater because the center of mass ...


30

How hot (or cold) something feels is not just down to temperature, but to the rate of heat transfer, or thermal conductivity. Popped corn is a good insulator, having a foam-like structure. As a result, little heat escapes to the hand. Unpopped corn is a much better conductor of heat, and transfers heat to the hand much more quickly, so that it feels much ...


29

Weather is... complex. Turning water vapor to solid releases heat, but this happens up in the sky. You end up with somewhat hotter and drier air somewhere at altitude and some amount of snow that falls down. (If "down" is hot enough, you get rain instead. The rain almost always starts as a snow.) The point is, you may, or more often may not get the ...


28

I do exactly the same. It is a very effective way of defrosting food fast. Compared to air water has a much higher heat capacity and a much higher thermal conductivity. That means heat flows from the water into the sausages much faster than it would in air and the water cools less than air would as it heats the sausages. Aluminium foil has a much, much ...


26

Sand paper removes material. When used properly, that removal of material can make a blade sharper. However, when cutting the sandpaper, there is no attempt to structure the removal of the material. It will simply dull the scissors. It will remove material in a relatively haphazard manner, taking off the sharp edge. If you have any questions of this, ask ...


25

The soap bubbles are a side-effect of the cleaning process. It is the mixing of air with the soapy water, and the film stability of the resulting bubble walls, that generates and maintains the bubbles. (Note that soap bubble liquid contains glycerine, which is a powerful film stabilizer that makes the bubbles last as long as possible). Note also that it is ...


23

For steel wool the combustion reaction is roughly: $$\require{mhchem} \ce{2 Fe (s) + 3/2 O2 (g) -> Fe2O3 (s)}$$ So the object 'absorbs' (and chemically binds) air oxygen and thus gains weight.


22

Stretching rubber makes it shiny Image credits: onelittleproject.com We know, balloons become highly reflective after inflation. This effect applies to rubber bands too. Rubber has a highly coiled structure, which scatters light randomly, giving it a soft appearance. Image credits:Balloon science Upon stretching, the coils unwind and reflect more ...


22

The bigger (and longer) the object, more will be the torque experienced by it. Let's say the length of the chalk we have is $\frac{L}{2}$ (Chalk 1) and $L$ (Chalk 2). When the chalk falls on the floor, it's most likely to hit on one of its edges. Given that it is dropped from the same height, the force on the heavier mass (Chalk 2) will be more than the one ...


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