Hot or Cold Material?: A Simple Touch Experiment
We recently conducted a poll asking people what sense they were most sensitive to between touch and smell. In one group 70% of the voters selected touch. But did you know that our hands are not always reliable thermometers? What appears to be cold or hot may in fact be the same temperature. This week we share with you a very simple experiment from Exploritorium that helps teachers explore everyday thermodynamics with their students.
Author: Siphilele Magagula
Image: Courtesy of Exploritorium
Ever wondered why the floor feels cold when the carpet feels warm in the same room under similar temperature conditions? We perceive certain materials to be ‘cold’ while they are actually at room temperature. This is due to heat being extracted from our hands when we touch them. Let’s learn how.
A Very Simple Experiment
The following experiment was developed by Exploritorium, a public learning laboratory based in San Francisco, which presents a plethora of child-friendly scientific experiments.
Materials Needed:
Image: Courtesy of Exploritorium
Get a variety of Various materials:
Metal,
Wood,
Styrofoam,
Glass,
Plastic,
Cardboard,
Any other material available with a flat surface larger than the size of your hand, and
An infrared thermometer (the inexpensive kind works fine)
How it goes:
Allow an hour or so for all the materials to come to room temperature before you begin
Place your hands flat on the various surfaces and compare how cold they feel,
Arrange the materials in order from cold to warm,
Use the infrared thermometer to measure each surface,
Notice that all the materials are at the same temperature.
The Science of Touch & Temperature: Understanding Tactile Perception
The heat extraction from your hand is a key factor in the perceived heat of different materials. When touching an object after the skin cools down, temperature sensitive nerve endings in your skin perceive the object to be cold. In addition, for an object to be perceived as cold, it must be colder than your hand, and must extract your body heat away, cooling down your skin.
When materials are at thermal equilibrium (material bodies at the same temperature), heat is still transferred between them and their surroundings, however the rate of heat transfer between each material varies. For example, when we touch a metal object and our body’s temperature is higher than the metal, its thermal equilibrium is disturbed. In an attempt to maintain its equilibrium, the metal will extract heat from your body, resulting in our hands feeling cold at the touch of metal.
The rate of heat transfer is much faster with metals than other materials such as wood, therefore wood does not feel as cold as metal. Conversely, if a metal object is hot and our body temperature is lower, our hand will perceive it to be very hot compared to a wooden object that is equally hot.
Observations
Sensory input affects how we react to materials within interiors, therefore it is important to observe and take into account people’s sensory perception. This knowledge could be used to better specify materials in space to produce the desired stimuli.