[INTRO ♪].

Imagine it’s a hot summer day, and you grab a nice, refreshing popsicle out of the freezer. But right after it closes, your brother says he wants one, too.

And when you go to open the freezer a second time, the door won’t budge. You might call your brother over to investigate this little novelty, but by the time he finally gets off the couch, the freezer’s easy to open again. So he impatiently grabs his popsicle and leaves.

But why is the freezer harder to open the second time? And why doesn’t the effect last? Well, it’s because of thermodynamics, which is basically the answer to most physics questions.

You might think this effect has something to do with the magnetic strip that holds the freezer closed. But the magnets are always there, and they don’t get stronger after you open the door. This effect is also more noticeable in the summer, when the air outside the freezer is warmer.

Earthly temperatures don’t really affect most magnets. But, if anything, magnets would work slightly worse in the hot summer. Atoms can’t line up as well to make a single magnetic field when they’re jiggling around a lot, like they do at higher temperatures.

So, hypothetically, the freezer door would be easier to open when it’s hot, which isn’t what happens. So... magnets are out. But the fact that air temperature matters is the key to what’s really going on.

Before you open the freezer, the air inside and outside are at the same pressure. The gases are pressing against both sides of the door the same amount. But after you open it, warm air from the room rushes in and displaces the colder air inside.

Then, when you close the door, the freezer starts doing its thing: it cools the warm air down. Gases like air exert less pressure on the world around them as they cool. At lower temperatures, molecules in the gas move more slowly and bump against their surroundings with less force.

So outside the freezer, there’s warm air at atmospheric pressure. And inside the freezer, you have cool air at a slightly lower pressure. Opening the door a second time means overcoming both the magnets holding it closed and the extra pressure from the room.

And that takes more force than just overcoming the magnets like you did the first time you opened it. The warmer the room, the bigger the temporary pressure difference, and the harder the door is to open. As time goes by, air leaks in until the air pressures inside and outside balance, and then the freezer is easy to open again.

So it’s not all in your head. And the universe isn’t, like, sending you a message about snacking on too many popsicles or bagel bites. It’s just thermodynamics.

But then again, isn’t everything? Thanks for watching this episode of SciShow, and thanks especially to our patrons on Patreon who make this show possible. If you want to become a part of our curious community, and even get the chance to ask us a question, you can go to patreon.com/scishow. [OUTRO ♪].