Physics

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Video

Materials

• 2 plates or plate-like objects - One of these should feel cold to the touch and the other warm. Examples are: ordinary plate (cold), saucepan lid (cold), paper plate (warm), plastic bowl lid (warm), frisbee (warm).
• Ice cubes

Short explanation

The plates in your demonstration both have the same temperature as the room, but one feels colder because it conducts heat better. This means that it conducts heat from your hand and makes it cold. It also means that it conducts heat to the ice cube and makes it warm.

Long explanation

Temperature is a measure of how fast a substance's constituent particles move. In hot water, for example, the water molecules move around quickly, while in cold water they are slower. If the water molecules move slowly enough, they get stuck in a certain configuration - the water has frozen to ice.

The fascinating thing about temperature is that humans have the ability to register it. Somehow the body can "measure" how much the particles in a substance move. Exactly how this happens is still not fully understood, but it does include several types of specialized nerve cells that send signals to the brain when they detect heat or cold.

When two objects come in contact with each other, the temperature is spread between them. This is done by the particles in the warmer object colliding with the particles in the colder and thus transferring kinetic energy to them. This transfer of kinetic energy through direct contact is called conduction. Energy that is being transferred through conduction - or radiation - is called heat.

Some materials conduct heat better than others. This means that the conduction goes quickly inside the material, but also to and from the material when it's in contact with another material. For example, metals are known to conduct heat quickly, which has to do with how the atoms in metals are organized. More specifically, there are free electrons that can easily transport energy.

The interesting thing about the temperature sense is that we do not really know the temperature of the object we touch. Instead, it's the temperature in our own hand we feel. For example, if you touch a metal, the metal takes heat from you and makes your hand cold. You then feel the metal as cold, even though it's actually your hand that is cold. Sure, the metal is colder than you - otherwise heat would be conducted from the metal to you instead - but not as cold as you perceive it.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

• What happens if you compare two plates of the same material but of different sizes?
• What happens if you compare two identical plates but put a drinking glass over one of the ice cubes?
• What is the significance of the contact area between the plate and the table?
• What can you find that conducts heat the best?
• What can you find that conducts heat the worst?

Varianter

A simpler version is to just place the ice cubes directly on different floor or table materials, or on different materials outdoors.

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