You're going on a picnic and you want to take along a hot drink, so you put it in a thermos so it will stay hot. Or maybe it's a hot day and you put a cold drink or water in a thermos to keep it cold. Have you ever wondered how a thermos can keep things both hot or cold? Take this quiz to see how much you know about your thermos.
Thermodynamics refers to heat transfer, where heat naturally moves to a cooler place to create an even temperature.
When atoms move they create heat.
The speed the atoms are moving at determines how much heat is produced. The faster they go, the more heat is produced.
At the temperature of absolute zero there is no atomic movement.
When atoms collide they transfer heat. It's a bit like billiard balls colliding. When one ball hits another, the second ball picks up momentum from the first ball.
Conduction refers to the transfer of heat through atom collisions.
Metal is a good conductor, which is why, if you heat the end of a metal rod, the other end will quickly become hot.
Infrared radiation is a form of light, but it is outside the spectrum visible to the human eye.
Black objects best absorb infrared. The absorption of infrared causes an increase in atomic motion, leading to a rise in temperature. So if you want to stay cool, it's best to wear light-colored clothing!
About half of the sun's energy that makes it to Earth is infrared radiation, which we experience as warmth. The rest is visible light.
Convection is the cycle of warm particles rising while cooler particles fill their space, heat up, and rise as the cycle continues. Convection affects both liquids and gases since, when these media get warm, the warm particles rise above both.
The purpose of a thermos is to reduce the transfer of heat.
A thermos is built based on the principle of insulation.
Foam is a good insulator because both the plastic in it and the air trapped in it are poor conductors and because convection cannot take place effectively since air in the foam is broken into tiny bubbles.
In a vacuum there are almost no atoms, which means there cannot be conduction or convection -- ideal in a thermos. Although it is almost impossible to make a perfect vacuum with zero atoms, a good thermos can get close.
Silvered glass acts as a mirror, reflecting infrared radiation away.
The heat loss in the imperfect vacuum is not significant compared to the heat lost through the cap. Also, the glass meets the walls at the top of the flask , creating a conduction path.
It doesn't know -- or care. It stops heat transfer, be it inside or outside the flask.
Although you might think bubble wrap would help with insulation, you need something sturdy, like metal or plastic, to protect the fragile glass inside.
A space shuttle generates a lot of heat from its engines and electronics, as well as from solar radiation. Its cargo bay doors are lined with radiators that dissipate the heat. One of the first things astronauts do once they reach orbit is turn on the radiators to cool down the ship.