why a glass jar can be opened more easily if the metal lid is heated gently first?
116652
Because heat causes molecules to separate (expand). The metal lid has a lower liquifying temperature than the glass, and voila! It expands more than the glass, breaking the seal and opening more easily.
204918
Just to clarify what these two folks have said, a metal doorknob seems colder than carpet even if the two are the same temperature... the metal pulls heat out of your hand quicker. Generally speaking, the carpet won't quite be the same temperature though; because heat passes through it at a slower rate, it will always be a more moderate temperature than the doorknob. So the doorknob will be hotter on a hot day and colder on a cold day.\n\nHope this makes it simple to understand.
1003680
The lamp consists of an illuminating bulb, and a glass bottle containing a transparent liquid, translucent wax, and a metallic wire coil. The glass bottle sits on top of the bulb, which heats its contents. The metallic wire coil is hidden in the base of the lamp, which the glass bottle is sitting on.\n\nThe wax is slightly denser than the liquid at room temperature, and slightly less dense than the liquid under marginally warmer conditions. This happens because the wax expands more than the liquid when heated.\n\nThe light bulb heats the container at the bottom, and due to heat exchange with the atmosphere, the container eventually dissipates the introduced heat. This method of heat transfer is called convection.\n\nWax at the bottom heats until it melts, and eventually becomes less dense than the liquid above it. At this time, a portion of the wax rises towards the top of the container. Near the top, away from the heat source, the wax cools, contracts, and as its density increases it begins to fall through the liquid towards the bottom of the container again. The difference in temperature between the top and bottom of the globe is only a few degrees.\n\nOne mass of wax may rise as another falls. The metal coil at the bottom helps to overcome the surface tension of the individual wax droplets, causing the descending blobs to agglomerate into a single molten wax mass at the bottom of the container. The cycle of rising and falling wax droplets continues so long as the bottom of the container remains warm and the top of the container remains cool. Operating temperatures of lava lamps vary, but are normally around 60 °C (140 °F). If too low or too high a wattage bulb is used in the base, the "lava" ceases to circulate, either remaining quiescent at the bottom (too cold) or all rising to the top (too hot).\n\nChaotic behaviour makes the movement of the wax unpredictable—hence lava lamps can aid in the generation of one-time pads for cryptographic use.\n\nThe colour of the wax and the liquid often varies and can be found in many different combinations.
888554
Strangely enough, the HOT water would freeze first.  There is a chemical explanation for this.
649898
No, that is not true.  If you have a more dense metal, it may take more energy to heat it up, but that is because there is more mass.  Water has a very high specific heat, but it is definately less dense than metals.  I believe specific heat is determined by quantum mechanical properties.
215023
Tap the side of the lid a few times gently in the direction that the top would open with the handle of a butter knife (not a sharp knife, please). It should open then.
619332
The container, because it's in contact with the outside environment, is a heat sink/source and thus it will be at a slightly lower or higher temperature than the solution.
1177517
By rubbing the lip, you're vibrating the glass. When you rub it at the right speed, it stars vibrating at its resonant frequency, and it makes that noise.\n\nThe resonant frequency of an object is kinda like a swing. If you push and pull at the right time (the resonant frequency), you can make the swing go higher and higher. If you push at the wrong times, you're not going to get anywhere.
197818
some glass reacts to vibrations in a way to make it shatter. (even vibrations you can't feel or hear) Another reason could be that it was previously exposed to severe temperature changes and was not made of tempered glass. any additional temperature changes might be the straw that broke the camel's back and it just broke when the room temp changed by a few degrees
1066345
Glassware to be heated should have a low thermal expansion co-efficient - basically, it should not change size or shape on rapid heating or cooling making it resistant to "heat shock".
440639
to stop condensation forming on the lid and dropping into the agar
598272
it makes the container stronger and less likely to dent or crinkle.
341668
Water evaporates at 100 degrees, celsius, so the liquid water you touched wouldn't be any hotter than that. The metal, on the other hand, does not. So it would be as hot as the object which is heating it.
106734
It depends on the relative humidity. The location with more relative humidity will cause more "sweating" or condensation on the outside of the glass. \n\nThis will usually be indoors, since it is usually drier indoors, thanks to air conditioners in the summer, and heaters in the winter.
293478
both will have a miniscus and this is due to the adhesive property of water. the cohesive property keeps the water molecules togherter but the adhesive props allow for movement as in a cappilary tube. the gLass is clearer than the plastic so im thinking glass
217015
One could argue plastic wrap since the Aluminum foil would allow for greater heat conduction into the orange from the air.\n\nAluminum, being a metal, is a good conductor of heat.  The metal foil will allow for heat from the "hot" air to be conducted into the "cold" orange much quicker than the plastic wrap would.\nI dont think the light enegry being absorbed or reflected is that significant.\n\nTake the opposite case as an example, say you had a hot metal pot of water an you wanted to set it on some surface so that it stays hot the longest.  If you set the pot on a metal cooking sheet, the heat will be conducted away from the pot and into the air much quicker than if you were to set it on a peice of wood for example.
338498
There are different types of glass, with different specific heat values.  Specific Heat is also called Heat Capacity.\n\nFlint Glass   0.503 Joules / gram Kelvin\nPyrex Glass   0.753 Joules / gram Kelvin