THE COLDEST BOOK IN THE WORLD COLD & HEAT Water 20 °C 293 K

Hot is related to the agita- tion of particles in . The col- der it is, the less agitated the particles, even in matter. The absolute Water zero, as defned by the Kelvin scale, 0 °C corresponds to the state in which par- ticles stop moving completely. Quan- 273 K tum physics would proceed to show Cold that they still can move a little.

Liquid -195,8 °C 77,4 K Ver y cold

Absolute zero -273,15 °C 0 K Absolute zero In 1742, Anders Celsius invented a temperature scale in which 0° and 100° respectively correspond to the and points of water. In 1848, Lord Kelvin introduced the concept of “absolute zero”, which corresponds to the lowest pos- sible temperature. COLD & In 1662, Robert Boyle showed that the pressure of a is inversely pro- portional to the volume it occupies. This was the frst of many discoveries in the feld of physical properties of gases.

Vacuum pump used by Boyle for his experiments. Te volume experiment At high temperature At low temperature

When you lower the tem- perature of a gas (here with cold nitrogen ), its particles become less agitated and its volume decreases.

At high temperature At low temperature COLD & In 1873, Johannes van der Waals formulated an equa- tion that shows that a gas becomes when it is cooled because its molecules are attracted to each other. Te liquefaction experiment At high temperatureAir liquefactionAt low temperature

When a metal is cooled with , it reaches a temperature of -196 °C and the air around it becomes cold enough for its oxygen to liquefy. The drops that form on the metal surface are liquid oxygen. All gases become liquid when cooled because their molecules become attracted to each other and prefer to condense when they move less.

At high temperature At low temperature In 1877, Raoul Pictet, in Switzerland, and Louis Cailletet (in the pic- ture), in France, independently came up with distinct methods to pro- duce liquid oxygen. COLD & THE LEIDENFROST EFFECT In 1756, Johann Leidenfrost wrote a treatise about some of the properties of water, amongst which the strange behavior of a drop of liquid that is placed on a hot plate. Te Leidenfrost experiment At high temperature At low temperature

When a drop of liquid is placed on a plate that is at a much higher tempera- ture, it evaporates. A thin layer of then forms under the drop. This layer isolates the drop from the heat and suspends it above the surface. That is what happens when drops of liquid nitrogen get in contact with a hot plate that is at room tempera- ture. At high temperature At low temperature COLD & Among other things, Thomas Young is renowned for his work at the beginning of the 19th century on the mechanical properties of solids, their elasticity and the deformation they undergo under stress. When a liquid has sufciently Indeed, at low temperature, the Tey stop moving, arranging in a fxed position. When a solid cooled, it becomes a solid (with particles are not agitated enough themselves in a more or less or- is cooled, it contracts because its the exception of ). for atoms to move freely. derly fashion according to the atoms move less and come closer material. But they keep vibrating together. Most solids contract when cooled, but do not become fragile.

Only a few solids become breakable, rubber for ins- Cold plants are very fragile as well because the tance: its long molecules cannot move around or water they contain turns to ice and becomes brittle. glide along each other any longer. COLD & MAGNETS In 1895, Pierre Curie defended his thesis on magnetic mate- rials and their behavior, which changes according to tempera- ture. He measured the magne- tic force these materials created when put in a varying magnetic feld. Te magnetic experiment At high temperature At low temperature

In magnets, atoms carry small quantum magnets called spins. These spins are all arranged in parallel, which explains the exis- tence of the North and South Poles and the magnetic properties of magnets. But when a magnet is heated above Curie temperature, its spins become disorganized and fuctuate. Its magnetization then disappears; the material is no longer magnetic. This is what happens here to gadolinium at above 20 °C. At high temperature At low temperature COLD & METALS In 1827, Georg Ohm published his theory of electricity, in which he showed that the electric cur- rent in metals is proportional to the voltage. Te conductivity experiment At high temperature At low temperature

In metals, electrons behave as waves among atoms. But the vibrations of atoms caused by heat slow them down. When metals are cooled, their atoms vibrate less and the electrons can therefore move more freely. The electrical resistance of the wire then decreases. That is why a bulb will light up more easily when its wire is cooled. At high temperature At low temperature COLD & In 1911, Kammerlingh Onnes discovered superconductivity while studying mercury. Te superconductivity experiment At high temperature At low temperature

At very low temperature, some metals become super- conductors. Their electrons suddenly form a sort of gigantic quantum wave. Not only do these materials then conduct electrical cur- rent perfectly, but they also expel their magnetic felds. That is why they are able to make magnets levitate. This phenomenon can be obser- ved here in cuprate, which behaves as a superconductor At high temperature At low temperature at a much higher tempera- ture than is usual for metals. A book by Marjorie Garry

Created and illustrated by : Marjorie Garry

Vidéo by : Written by : Marjorie Garry Julien Bobrof & & Pierre Klein Frédéric Bouquet

Translated by : Mélanie Mora y Collazo

Tis book is the result of the colla- It benefted from the support of boration between Marjorie Garry, the “Physics Reimagined” Chair who studies Scientifc Illustration supported by the Fondation at Ecole Estienne (DSAA), and Paris-Sud and by the Air Liquid the team of “La Physique Autre- Group. ment” (Laboratoire de Physique des We would like to thank Matthieu Solides, Université Paris-Sud and Lambert (Ecole Estienne), the CNRS). MOUS team and Vincent Klein (LPS). -- . .-. -.-. .. .- .-- .. .-.. .-.. -.--