what is the significance of thermal expansion in human life?

I'd like to add to poldi's answer - the amount of expansion for a given change in temperature is bigger for the metal jar lid than it is for the glass jar - there is a differential thermal expansion. Note that, if you had a glass lid stuck on a metal jar, you'd put it in the freezer to shrink the metal jar! (Additionally, the metal jar lid has a lower "thermal inertia" - a combination of mass and specific heat capacity, which means it heats up faster than the glass.)

Some other thermal expansion considerations that are applied to daily life:

Ever drive across a bridge? Or especially, ever ride a bike or a motorcycle across a bridge? The bridge is built with joints that allow it to expand in the heat of summer and contract in the cold of winter. If the bridge weren't free to move, it would crack and buckle. But the joints can be a hazard for bikes and motorcycles. (Just like with the jar, this is related to

Ever use one of the old mercury thermometers to take your temperature? When you put the thermometer in your mouth, you heat up the mercury to your body temperature, and it expands into the small tube; the distance it goes up the tube tells you what your temperature is.

Do you have a fancy electronic thermostat in your house? If you don't, then open it up. You'll see a coil of metal inside. That coil is actually made of two layers of metal (called, appropriately, a bimetallic strip). The different metals have different thermal expansion properties - one expands more than the other for a given change in temperature. Think of a pool noodle, standing on its end, like this:

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Now, if you bend it into a shape like this

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the material on the right side of the noodle is shorter than the material on the left side. Now, if instead of bending the noodle directly, you could somehow make the material on the left side contract, you would get the same bend. That's what the differential thermal expansion in the bimetallic strip does - when the temperature goes down, one side of the strip contracts more than the other, which makes the strip bend toward the contracted side. When the temperature goes up, the bend is reversed, as one side expands more than the other.

The coil in the thermostat takes advantage of this, changing the angle of a mercury switch (the metal mercury, which is liquid at room temperatures, slides over two electrical contacts to complete a circuit when the switch is tilted one way, and away from the contacts to break the circuit when the switch tilts the other way).

One last example - do you have any dental fillings? If you do, they're made out of a material that was chosen to be a good match to the thermal expansion coefficient of your teeth! Otherwise, when you drink hot tea or eat ice cream, the difference in thermal expansion would loosen your fillings and maybe crack your tooth!

I hope that helps!

I thinks that many people have been socialized to believe that the human race is superior and 'precious', myself included, which is a very human thing to do. But every now and then I do find myself thinking about life and coming to the conclusion that we are just the same as any other animal - each animal, each species is different, including us. I mean... we can't fly, birds can. I still lean to think that humans are slightly more precious, not incredibly so, but we (unlike any other species) have evolved to human and built things on a massive scale, communication devices, boats, planes... we have the capacity to love and hate. We also have power, which is getting to people's heads, neglect, fights etc. It's all about competition. In that way, we are just the same as any other animal. --------- To be honest, just then i started rambling, and don't know if i answered your question. But you have some of my... insane thoughts.

If the metal lid on a jar is too tight to get off, running hot water over the lid causes it to expand a bit, makes it easier to open the jar.

First, you need to be able to find your @$$ with both hands.

Next, you need to post to the right category.

As a last resort, study the subject, much as it may be beyond your grasp.

No idea, but fascinating.

Rings/fingers swell up in the heat making them hard to get off.