Actually, even if the thermometer is not mercury filled (and most are not nowadays, it's considered too dangerous in the event of a broken thermometer), they usually depend on a spirit-filled hydrocarbon fluid (Kerosene, iso-amyl-acetate, and pentane for example), however the result is the same:
Shaking the thermometer forces the fluid in the thermometer back down to where it needs to be to give an accurate reading. As the interior of a thermometer is in a vacuum (more or less), there's not really any air to help push the fluid back into the bulb after it rises up through the thin passage where we get our reading, so shaking ensures that the fuid has returned fully to the bulb as much as it should be at the current temperature.
Hope that helps, and you have a great day!
Asuka Jr.
Shaking the thermometer forces the fluid in the thermometer back down to where it needs to be to give an accurate reading. As the interior of a thermometer is in a vacuum (more or less), there's not really any air to help push the fluid back into the bulb after it rises up through the thin passage where we get our reading, so shaking ensures that the fuid has returned fully to the bulb as much as it should be at the current temperature.
Hope that helps, and you have a great day!
Asuka Jr.
