Key Concepts
Temperature
Heat transfer
Thermal sensitivity
Thermodynamics
 
Introduction
Thanks to our sense of touch, we can all tell the difference between hot and cold. But does the same temperature always feel the same? Have you ever noticed that the bathroom tile feels very cold to your bare feet but your towel, which has been hanging in the same room, feels warm? Why is there such a difference? Try this fun activity and find out!
 
Background
First we need to consider energy. Heat is a form of energy. When an object gains heat the object's molecules gain kinetic energy and they move faster. Temperature is the objective measure of the average speed of the molecules.
 
Next we need to consider our sense of touch. Your brain is always sending messages to your hands: "Hey, hands! Grab the doorknob and open the door!" And they return messages, too. Sensory cells in your hands send signals to your brain so it can figure out what your hands are touching. But, as you will find out in this activity, our sensory system doesn't process temperature quite as objectively as a thermometer might.
 
Materials

  • Bathroom with tiles
  • Metal towel rod
  • Towel
  • Empty water glass
  • Paper and pencil
  • Liquid crystal aquarium fish tank thermometer strip (available at pet stores)
 
Preparation
  • Make sure the towel and the glass are in the bathroom you will be using for the activity for at least 10 minutes before you begin the activity.
  • Make a list of the items you will be testing: tile, towel rod, towel, glass—and leave space for two notations: how it felt to the touch and what temperature it actually was.
 
Procedure
  • Place your palm on the towel. Does it feel warm or cold to the touch?
  • Write down how it felt to the touch.
  • Now place your palm on the surface of the empty glass. Does it feel warm or cold?
  • Again, note your observation on paper.
  • Continue the same process with the towel rod and the tiles. How do they feel to the touch? Note your assessments. Was it easy to feel a difference in temperature among the different objects? Wait a few minutes and then hold the thermometer strip to the surface of the towel. What is the temperature reading?
  • Note this on the paper.
  • Now take the temperature of the glass, the towel rail and the tile. Are the surfaces the same or different temperatures? How does this compare with the sensation you felt when you touched each object?
  • Extra: Obtain three tall glasses. Fill one with hot (but not scalding) water, another with ice water and the third with room-temperature water. Hold onto the ice-cold glass with one hand, making sure your palm is in full contact with the glass. Now hold onto the hot glass in the same manner with the other hand. Keep both hands on the glasses for one minute. Now put them down and immediately grasp the room-temperature glass with both hands. Is the glass hot or cold?

 
Observations and results
The objects in your bathroom—the towel, glass, towel rod and tiles—should all be about the same objective temperature. But the temperature you sense from your hand might be vastly different. This has to do with how heat—or energy—moves. When two objects are at different temperatures, heat flows from the hotter one to the cooler one. The metal towel rod probably felt the coolest because metal is a good heat conductor. That means it will rapidly sap heat from your hand, which makes you sense it as cold. The towel, on the other hand, is made of cotton, which is a poor heat conductor. It doesn't suck away your hand's heat, so it seems warmer to the touch. The glass and the tile might have been somewhere in the middle. The way we perceive temperature is by comparison. When you touch an object that is a different temperature than your hand you interpret the flow of heat to or from your hand as the sensation of thermal difference. When heat flows from the skin, its temperature decreases and its sensors "fire" to indicate that the skin is in contact with a cooler object.
 
Because determining temperature using our sense of touch is comparative, to objectively measure temperature you need to use a thermometer.
 
If you tried the "Extra" activity, you will see that even your two hands can give you conflicting information if the conditions are right. The hand that held the cold glass told you that the room temperature glass was hot. The hand that had held the hot glass said the room temperature glass was cold. But both hands were holding the same glass—weird!
The mixed-up sensations demonstrate how your hands do not sense the temperature of the glass directly. The heat sensors in your skin sense the temperature change caused by heat—or energy—flowing into or out of your hands. When you held the cool glass, your hand got cold. When this cold hand held the room-temperature glass, heat from the glass flowed into your hand to warm it up. Your cold hand gained heat, so it sensed that the glass was warm. When you held the hot glass, your hand gained heat; when your hot hand held the room-temperature glass, heat from your hand flowed into the glass to cool your hand down. Your hot hand lost heat, so it sensed that the glass was cool.
There are nerves in your hand that can tell if an object is warmer or cooler than body temperature. But they quickly adapt, and the object starts to feel "normal"—neither warm nor cold. When you moved your hands to the glass filled with room-temperature water, each hand sensed a change from what it had been feeling. Because each hand was holding a glass of a different temperature previously, the change each felt was different—even though they were touching the some thing.
 
More to Explore
Heat and Thermal Energy, from Physics4kids.com
Heat Transfer, from PBS
Testing Heat and Temperature, from the University of Illinois
 
Why Does the Floor Feel Cold When the Towel Feels Warm? was developed by Exploratorium and is featured on page 25 of Exploralab: 150 Ways to Investigate the Amazing Science All around You. Created by Exploratorium, Exploralab is a book that takes curious kid scientists, ages 8–12, through 24 hours' worth of household investigations, experiments and discoveries.

This activity brought to you in partnership with Exploratorium

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