Why do metals seem colder although they have the same temperature?

By Anonimski - Own work, CC BY-SA 3.0, Link

All the objects that have been inside your room for more than one hour are at room temperature. That is because heat flows from hotter to colder objects, so if you put a cold object inside the room, heat will flow to it until it reaches room temperature.

If we touch a piece of metal that is inside the room it feels cold. But when we touch the other objects of the room they don't feel as cold. Why is that? Why do metals seem colder than the other objects in the room although they have the same temperature?

Please, explain your reasoning. You can post your attempted answers in the comment box below. Please, do not use Facebook or Twitter to give your answers.

Preparation for the International Physics Olympiad (IPhO): Thermodynamics and Statistical Physics

The IPhO Syllabus includes:

2.7 Thermodynamics and statistical physics

• 2.7.1 Classical thermodynamics: Concepts of thermal equilibrium and reversible pro­cesses; internal energy, work and heat; Kelvin's tem­perature scale; entropy; open, closed, isolated systems; first and second laws of thermodynamics. Kinetic the­ory of ideal gases: Avogadro number, Boltzmann factor and gas constant; translational motion of molecules and pressure; ideal gas law; translational, rotational and os­cillatory degrees of freedom; equipartition theorem; in­ternal energy of ideal gases; root-mean-square speed of molecules. Isothermal, isobaric, isochoric, and adiabatic processes; specific heat for isobaric and isochoric pro­cesses; forward and reverse Carnot cycle on ideal gas and its efficiency; efficiency of non-ideal heat engines.
• 2.7.2 Heat transfer and phase transitions: Phase transitions (boiling, evaporation, melting, subli­mation) and latent heat; saturated vapour pressure, rel­ative humidity; boiling; Dalton's law; concept of heat conductivity; continuity of heat flux.
• 2.7.3 Statistical physics: Planck's law (explained qualitatively, does not need to be remembered), Wien's displacement law; the Stefan- Boltzmann law.

Members of the Spanish National Team can download the notes here:

• Introducción a la termodinámica y a la física estadística

Some cognitive conflicts involving Thermodynamis and Statistical Physics:

• Cognitive Dissonances: Thermodynamics and Statistical Physics

It is also useful to follow the IPhO's Study Guide by Jaan Kalda:

• Study guide for IPhO-s: Thermodynamics

Here you can find the solutions to some of the problems:

• Pr 1 & 7: [IPhO1996Theory1] Problem Solution
• Pr 6 & 34: [IPhO1992Theory3] Problem Solution
• Pr 24: [IPhO1989Theory1] Problem Solution
• [IPhO2007Theory] Problem Solution

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Why do ice cubes melt faster in fresh water than in salt water?

The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point.

The freezing point of a solvent is depressed when another compound is added, meaning that a solution has a lower freezing point than a pure solvent. This phenomenon is used in technical applications to avoid freezing, for instance by adding salt or ethylene glycol to water. If you live in a place that has lots of snow and ice in the winter, then you have probably seen the highway department spreading salt on the road to melt the ice.

Now, let us consider the following experiment:

1. Make two almost identical ice cubes.
2. Mix 1 teaspoon of salt in an 8 oz. cup of water. This will be our salt water cup.
3. Fill a 8 oz. cup with water, but with no salt added. This will be our fresh water cup
4. Place one ice cube into each cup simultaneously. Which ice cube do you predict would melt the fastest?

Naively, one would think that, according to the previous information, since salt lowers the freezing/melting point of water, the ice cube in the salt water cup should melt the fastest.

Nevertheless, if you carry out the experiment, it leaves no doubt. The ice cube in the fresh water cup melts faster!

Why do ice cubes melt slower in salt water? Please, explain your reasoning. You can post your attempted answers in the comment box below. Please, do not use Facebook or Twitter to give your answers.

I will give you a clue: repeat the experiment, but this time, after you place the ice cubes in the cups, wait 30 seconds and add a couple of drops of food coloring to each cup without disturbing the water in the cups.

Is expansion of gases a violation of inertia law?

The first Newton's law (also called inertia law) says that, when viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force.

Let us suppose that we have a box with a wall splitting it in two halves. The left half contains a rest gas (no wind inside), while the right half is empty. Suddenly, we remove the wall. Because of the fact that gases expand to fill their containers, we know that the gas of the left half will move to the right side in order to fill the whole box:

But there is no net force acting on the gas, so why has it moved to the right half of the box? Do gases violate the inertia law?

Are you able to give an explanation? Accept the challenge!