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Hands-on Activities

Is feeling always believing?

Grade
6 7 8 9
Jurisdiction
AB BC MB NB NL NS NT NU ON PE QC SK YT Outside Canada
Format

Summary

Get your hands cold for science and explore the topic of sensory adaptation.

What You Need

  • Bowls or trays (big enough to fit your hands) - 3
  • Water taps (for access to cold and hot water)

Safety First!

Be careful when using water from the hot water faucet. The factory setting on most hot water heaters is about 60C (140F). Skin contact with water directly from a hot water faucet can cause third degree burns after as little as 5 seconds of exposure. Do NOT try the following activity using hot water directly from the faucet.

What To Do

  1. Fill one bowl 1/2 full with ice (or cold) water, another bowl with warm (not hot) water and the last bowl with room-temperature water.
  2. Arrange the bowls in a straight line.
  3. Put one hand in the cold bowl and another in the warm bowl and leave them there for a minute or so. Quickly plunge both hands into the room temperature bowl. What temperature does your left hand register? What about your right hand? Why do you think they feel that way?

Discovery

What’s happening?
  • This is an example of neural adaptation (or sensory adaptation), which is the change over time in the responsiveness of the sensory system to a constant stimulus.

When thermoreceptors get used to a certain amount of heat or cold they get a little “lazy.” Usually, nerve cells will sense something and send a signal to your brain through your nervous system to say that there’s something hot or cold touching you, but that’s not always the case. If you accidentally touch something really hot with your finger, the heat receptors in that finger will sense it right away. Although very fast, it still takes time for that message to get all the way to your brain, be interpreted in the correct way, and finally send a message back to your finger that you are touching something hot. By moving your hand quickly from either cold or warm water to the room temperature water bowl, you notice the message is delayed and different temperatures are perceived by each hand even though the water in the bowl is the same temperature.

What’s happening?
  • This is an example of neural adaptation (or sensory adaptation), which is the change over time in the responsiveness of the sensory system to a constant stimulus.

When thermoreceptors get used to a certain amount of heat or cold they get a little “lazy.” Usually, nerve cells will sense something and send a signal to your brain through your nervous system to say that there’s something hot or cold touching you, but that’s not always the case. If you accidentally touch something really hot with your finger, the heat receptors in that finger will sense it right away. Although very fast, it still takes time for that message to get all the way to your brain, be interpreted in the correct way, and finally send a message back to your finger that you are touching something hot. By moving your hand quickly from either cold or warm water to the room temperature water bowl, you notice the message is delayed and different temperatures are perceived by each hand even though the water in the bowl is the same temperature.

Why does it matter?

This example illustrates what happens in the cold winter weather. After being outside in the cold for a while, the thermoreceptors get used to the cold and start to treat it like it is the "normal" temperature, so that if you put your hands under warm water, it feels almost like hot water. It also happens in the very hot, sunny summer weather: warm water may seem really cold on your skin, especially if you have a sunburn! In these cases, the sense of temperature depends on the direction of heat flow between the air and your skin: when heat flows from water to your skin, it feels warm. When the heat flows from your hand to the water, it feels cool.

We have many different types of receptors in our body and there are many other examples of sensory adaptation like those in the "Investigate Further" section, which include touch and taste. Other examples include sound and sight. You may have experienced adaptation to light if you have been in a dark room for a long time and then were suddenly exposed to light. Sound adaptation happens whenever you are in a noisy environment and then suddenly enter a very quiet place. How many other examples can you think of?

Why does it matter?

This example illustrates what happens in the cold winter weather. After being outside in the cold for a while, the thermoreceptors get used to the cold and start to treat it like it is the "normal" temperature, so that if you put your hands under warm water, it feels almost like hot water. It also happens in the very hot, sunny summer weather: warm water may seem really cold on your skin, especially if you have a sunburn! In these cases, the sense of temperature depends on the direction of heat flow between the air and your skin: when heat flows from water to your skin, it feels warm. When the heat flows from your hand to the water, it feels cool.

We have many different types of receptors in our body and there are many other examples of sensory adaptation like those in the "Investigate Further" section, which include touch and taste. Other examples include sound and sight. You may have experienced adaptation to light if you have been in a dark room for a long time and then were suddenly exposed to light. Sound adaptation happens whenever you are in a noisy environment and then suddenly enter a very quiet place. How many other examples can you think of?

Investigate further
  • Try other examples of sensory adaptation! Rub your index finger gently over a piece of coarse sandpaper a few times. After a minute or two, rub the same finger over the paper again. Does it feel as course as it was the first time, or does it feel smoother?
  • Take a sip of sugar water (dissolve 1 tablespoon of white sugar in a glass of water) and swish it around your mouth for a minute (but do not swallow it!). Spit it out, and then drink some fresh water. Did the fresh water taste how you expected it?

For more information on this topic check out these Let's Talk Science resources:

  • Neurons: The Building Blocks of Your Brain (Backgrounders) - How does your brain allow you to do and experience so much? It’s all because of the building blocks of your brain - neurons!
  • How fast can you react? (Hands-on Activities) - What is a reflex? Test your reaction time and find out why reflexes are important in this challenge activity.
Investigate further
  • Try other examples of sensory adaptation! Rub your index finger gently over a piece of coarse sandpaper a few times. After a minute or two, rub the same finger over the paper again. Does it feel as course as it was the first time, or does it feel smoother?
  • Take a sip of sugar water (dissolve 1 tablespoon of white sugar in a glass of water) and swish it around your mouth for a minute (but do not swallow it!). Spit it out, and then drink some fresh water. Did the fresh water taste how you expected it?

For more information on this topic check out these Let's Talk Science resources:

  • Neurons: The Building Blocks of Your Brain (Backgrounders) - How does your brain allow you to do and experience so much? It’s all because of the building blocks of your brain - neurons!
  • How fast can you react? (Hands-on Activities) - What is a reflex? Test your reaction time and find out why reflexes are important in this challenge activity.