What does temperature mean? You already know that the temperature is a property of an object, or substance that is measured using a thermometer. You know there are two temperature scales, the Fahrenheit scale and the Celsius scale. But when asked the question: “What does temperature mean?”, most people would answer “The temperature tells us how hot or cold something is.” Having a high temperature means the object will feel hot to the touch, and a low temperature means that the object will feel cold. To most people, temperature is all about how hot or cold something feels. To scientists, temperature means something very different. We use our sense of touch to tell us about the temperature of an object, but this sense is not a very accurate detector, and sometimes our ‘sense of touch’ can be misleading. Have you ever been told that you “feel hot” or that you “have a temperature”? When we are sick, our body temperature is often used to diagnose an illness or infection. Many times we can use our hands to feel if the person is warmer than normal, but to be certain a parent or a nurse will have to use a thermometer to actually measure the body temperature. ACTIVITY #8: Hot Finger – Cold Finger What Does Temperature Tell Us?

GOALS: GOALS: In this lab activity, you will … Learn that hot and cold are relative sensations, based on how an object feels, but there is nothing relative about the temperature of an object. Learn that your sense of touch makes a poor thermometer.

Part A – Can you tell if something is hot or cold? You will need three cups to do this investigation. Fill the first cup (8 oz) with very warm water, the second cup (8 oz) with cold water, and the third cup (20 oz) with lukewarm (room temperature) water Place your left index finger into the very warm water and your right index finger into the cold water. 3. Leave your fingers in the very warm and cold water long enough so that both of your fingers become accustomed to the water temperature. This may take seconds. 4. Then take both fingers and place them into the third cup, the one holding the lukewarm water. Make sure you place your fingers into the third cup of water at the same time.

Question #1: Are you surprised by what you feel? Question #2: Did both fingers feel the same when you placed them in the lukewarm water? Question #3: Do your left finger and your right finger agree on the temperature of the lukewarm water?

Part B – Repeating the Experiment with a Thermometer Arrange the three cups of water, one filled with very warm water, one filled with cold water, and the third filled with lukewarm water, just like you did in the first part. Check your thermometers – are displaying the same measurement? If not, record the difference in the two thermometers. Place the first thermometer in the very warm water, and the second thermometer into the cold water. It will take a few seconds for the thermometers to adjust to the temperature of the samples of water. When you are confident that the thermometer reading is the water temperature accurately, record the temperatures. Now place both thermometers into the third cup holding lukewarm water. Give the thermometers several seconds to adjust to the temperature of the water in the third cup, then record both readings.

Temperature of the very warm water thermometer reading________°C Temperature of the cold water thermometer reading ________°C Temperature of the lukewarm water thermometer reading ________°C Question #4: Do the thermometers agree on the temperature of the water in the third cup? Question #5: Did your fingers and sense of touch behave like the thermometers? Question #6: Which do you believe gives the best indication of temperature, your sense of touch or the thermometers?

The skin covering your fingers, toes, nose, ears, and most other parts of your body is equipped with ‘sensors’ that are very good detectors of ‘hot’ and ‘cold’. But these sensors do not make very good thermometers. Thermometers measure the energy of the particles. What does the sensation of hot versus cold, or warm versus cool depend upon?  Whenever heat energy is being transferred into your skin, the sensors signal that whatever you are touching is warmer than your skin. If large quantities of heat energy are transferred into your skin quickly, the message you will get is hot!!!  If heat energy is being transferred away from your skin, the same sensors signal that the object is cooler than your skin. When your skin signals cold!!! it is because large quantities of heat energy are quickly leaving your skin.  The sensors in your skin detect heat energy transfer, not temperature. If the object your finger touches is at a higher temperature than your skin, the object will feel warm or hot. If the object is at a lower temperature than your skin, it will feel cool or cold. Knowing this it is not hard to figure out why your fingers signaled that the water in the third cup was warm and cool at the same time!

Important lessons of this activity:  Warm, cool, hot and cold are not determined only by the temperature of the object, so be very careful about making judgments of temperature based on whether something ‘feels’ hot or cold.  Heat energy transferred into or out of your skin plays an important role in determining whether the object you are touching feels hot, warm, cool or cold.  Thermometers measure the temperature of an object or substance; your sense of touch does not.

So what does the temperature of an object represent? The temperature of an object is linked to something much more fundamental than hot or cold. The temperature of an object tells us about the energy of its particles. When the particles are more energetic, the temperature of a substance is higher. When the particles of a substance are less energetic, the substance is at lower temperatures. Thermometers are designed to detect the energy of the particles, not whether the substance feels hot or cold. Ø When the frying pan comes in contact with your hand (the particles of the frying pan are very energetic, so the temperature of the pan is high) some of the particles’ energy is transferred to your hand. The inward flow of heat energy triggers your nervous system to send a signal to your brain that the frying pan is hot. Ø Particles of air on a crisp winter’s morning have low energy, so the temperature of the air is low. When your face comes in contact with these particles of air, energy is transferred out of your skin to the air particles. This outward flow of heat energy triggers your nervous system to send a signal to your brain that the air is cold.

In your journal or notebook, write a concise summary of this activity. Be sure to address the following questions and use your data to support your responses. Is your finger, or body, a good indicator of temperature? What can the sense of touch in your skin detect? Using the Particle Model, describe the difference between an object at a low temperature and an object at a high temperature?

Investigating Further … Meteorologists typically use the “wind-chill factor” to describe the conditions outdoors during the winter. Since we know that our sensation of temperature is different from the actual measured temperature (this is what we found out in this activity), a formula was devised to estimate how cold it “feels” outside during cold weather conditions. Two polar explorers developed the equation more than 50 years ago. Major Paul Siple, a geographer, and Charles Passel, a geologist, performed tests using partially clothed subjects subjected to the Antarctic subzero weather. The men also performed 89 tests, at various temperatures and wind conditions that measured the heat loss from water-filled plastic containers that were hung from the roof of a building. The end result was a mathematical way to adjust the temperature by adding a “wind-chill factor” that was a measurement of the heat loss from exposed skin. Not everyone agrees on the wind-chill calculations and many scientists point out flaws in the original tests conducted by Siple and Passel. The World Meteorological Organization is currently attempting to create a worldwide standard for reporting the wind chill effect. Scientists are also attempting to create a “thermal comfort index” that could be used in hot weather as well as in cold weather conditions.