Snuggly Science: How Puppies Keep Warm
Have you ever woken up on a cold, frosty morning and just wanted to snuggle down deeper under the covers? Animals, like puppies and piglets, do not like being cold either, but they do not have hands or blankets to wrap themselves up. So when animals get chilled, they change their behavior and do things like huddle – they curl up close to other animals. In this science activity, you’ll see just how much huddling can help reduce heat loss.
Want makes a puppy want to sleep in an adorable heap? Snuggling, also known as huddling, does more than create cute puppy piles. Puppies, like other animals, huddle to keep warm. Heat is constantly flowing into and out of everything around you. Just as a ball rolls downhill, heat “rolls downhill” too, flowing from an object that’s hotter to one that’s colder. If, for instance, you put a cup of hot chocolate in a room-temperature room, the heat will flow from the hot chocolate to the room, cup and table. These surroundings will actually warm up from the hot chocolate’s heat. When the temperature of the hot chocolate cools down enough to reach the surrounding temperature, the heat flow stops.
Heat flows from a hotter object to a colder object in several different ways. For example, when puppies are huddling together to keep warm, they are reducing the amount of their bodies (specifically surface area) that is exposed to the colder open air, and so are reducing heat loss in two ways: by radiation and convection. A puppy also gains heat by another way – conduction – if the puppy it’s snuggled up to happens to be warmer.
- Four glass jars or bottles that are the same size and shape, with lids. Use jars whose lids do not stick out further than the glass sides of the jars. If using canning jars, you will need rings for the lids.
- Thermometer with a stem that has a range of at least 200 degrees Fahrenheit, such as a candy thermometer
- Large soup pot
- Measuring cups
- Oven mitts
- Timer or stopwatch
- Piece of paper and pen or pencil
- Using a hammer and a nail, carefully make a hole in the center of each jar’s lid, just big enough for the thermometer’s stem to fit through. If needed, slightly adjust the hole’s shape (using the nail) so that the thermometer’s stem sticks straight, vertically down in the jar. Why do you think you’d want to measure the core temperature of the jars?
- Fill the jars about three-fourths full with equal amounts of the same-temperature water. Each jar will be a model of a puppy.
- Fill the large soup pot with enough water so that when three jars are in the pot, the water level within the jars equals the water level outside of the jars (in the pot).
- Be careful when working with the hot water. Adult supervision is required when using the stove.
- Set a timer for ten minutes, or have a stopwatch ready.
- Put the large soup pot on the stove and put one jar inside. Put the thermometer inside the jar (going through the lid’s hole) so that the thermometer is held upright inside the water in the jar. Turn on the stove.
- When the temperature of the water inside of the jar reaches 190 degrees Fahrenheit (88 degrees Celsius), turn off the stove, immediately remove the jar from the water bath using oven mitts and dry the jar quickly on a towel.
- Immediately start the timer or stopwatch. Write down the water temperature inside the jar when you do this. Then continue taking water temperature measurements every two minutes for at least ten minutes. How does the temperature change over time?
- Repeat these steps but this time put three jars inside of the pot (instead of just one). Put the thermometer into one of the three jars. When the jar reaches 190 degrees Fahrenheit, remove all of the jars, quickly dry them and arrange them so that the sides of each jar are touching two other jars, forming a triangle. Write down the initial temperature in the jar, and then again take temperature measurements every two minutes for at least ten minutes. How does the temperature of the jar huddled with two other jars compare to the temperature of the one jar alone over time? At what time was the difference in their temperatures the greatest?
- Overall, what do your results tell you about how and why puppies and other warm-blooded animals huddle to keep warm?
Extra: Try repeating this activity but compare three jars touching to two jars touching or to three jars separated by an inch. How does the heat loss compare between these different configurations and to one jar alone?
Extra: Think of how you could add “fur” or “fat” to your puppy models in this activity and then try it out. How do these additions affect heat loss?
Extra: You could investigate increased heat loss through convection by blowing a fan on the jars. How does this affect how much heat is lost over time?
Observations and Results
Did the three jars huddled together lose less heat over time compared to the one jar alone? Was their difference in temperature the greatest at the end of the ten minute period?
Over time, you should have seen that the water in the jars – alone and in a huddled group of three – lost heat, but the jar alone lost heat faster than the three jars huddled together. The temperature of the water in the jars should have started out at about 190 degrees Fahrenheit, since this was the temperature immediately when they were removed from the pot. As just one example, the temperature of the water in the one jar alone may have then dropped to about 172 degrees Fahrenheit after ten minutes, while the temperature of the water in a jar huddled in a group of three may have only dropped to about 176 degrees Fahrenheit. (The exact size and shape of the jars affects how quickly they lose heat, as a larger amount of hot water will take a longer amount of time to cool down compared to a smaller amount of the same-temperature water, and the shape of the jars affects their total surface area.) When the jars are close together, just like puppies snuggling together, they help keep each other warm, primarily through conduction.
Ask an Expert
- How Do Animals Spend the Winter?, from Science Made Simple
- Energy, Heat Flow, and Life, from David Watson
- Fun, Science Activities for You and Your Family, from Science Buddies
- Huddle & Cuddle: How Puppies Keep Warm, from Science Buddies