Huddle & Cuddle: How Puppies Keep Warm
AbstractWhat is the first thing you do when you wake up on a cold, frosty morning? 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 mammalian biology science fair project, you will see just how much huddling can help reduce heat loss.
Kristin Strong, Science Buddies
This science fair project is based on the following California State Science Fair (CSSF) project, also a winner of the Science Buddies Clever Scientist Award:
Adler, D.L. (2009). Chill Out.
To determine how much huddling reduces heat loss in warm-blooded animals.
Is there anything cuter than a dozen puppies all sleeping together in a pile, like the ones shown in Figure 1, below? What makes a puppy want to sleep in a heap like that? Does his brother or sister make a good pillow? Probably so, but snuggling, also known as huddling, does more than create puppy pillows. Puppies, like other animals, huddle to keep warm.
Figure 1. This photo shows an adorable pile of puppies huddling together for warmth. (Flickr, 2007).
You might not realize it, but heat is constantly flowing into and out of everything that you see around you. See that tree? Think: Heat flow! See a rock? Think: Heat flow! See a puppy, a person, a shoe, a car, a key? Yep, think heat flow! Heat is everywhere.
Just as a ball always rolls downhill, heat "rolls downhill" too, and flows from an object that is hotter to an object that is colder. If, for instance, you put a cup of hot chocolate in a room-temperature room (and somehow manage to resist drinking it), the heat will flow from the hot chocolate to the air in the room, and from the hot chocolate to the cup, and to the table. The air, the cup, and the table will actually heat up a tiny bit from the heat of the hot chocolate. As the temperature of the hot chocolate gets close to the temperature of the air in the room, the heat flow slows down. When it reaches the temperature of the air, the heat flow between them stops until there is another temperature difference between them. Say, for example, somebody opens the door and lets in a blast of cold air, then the room air temperature will drop, and heat will flow, once again, from the cup to the air until they have an equal temperature again.
Heat flows from a hotter object to a colder object in several different ways:
- By direct touch (called conduction),
- On energy waves through open space (called radiation), and
- By the flow of liquids, like water, or gases, like air (called convection).
If you touch a warm cup of hot chocolate, for example, the heat energy in the cup will flow to the skin on your hands, and your hands will become warmer by conduction.
You do not have to touch something to get heat from it though. If you stand outside in the sunlight, you are receiving heat by radiation. You are not actually touching the Sun (thankfully), but the Sun's heat energy is flowing from a hotter object (the Sun) to a cooler object (you) on energy waves or rays. In fact, that ray of energy you feel right now left the Sun just 8 1/2 minutes ago and traveled 93 million miles through open space to get to you. What a trip! But the Sun is not the only thing that can radiate heat—everything acts like a little Sun. All the objects that you see around you, including you, are constantly moving heat into and out of themselves, as conditions change, through radiation. It is the reason why warm-blooded animals, including humans, need fur, feathers, fat, or clothing if they want to live in an environment that is cooler than their inside body temperature. Heat is constantly radiating off animal bodies into open space. A lot of food that a warm-blooded animal eats goes toward making heat to help its internal (inside) body temperature remain the same.
When it is windy, people and animals lose the heat from their bodies more quickly because of convection. In convection, heat is moved from warm bodies to the air as the wind blows by. It's the same thing that happens when you blow on hot soup. Your breath is like the wind, and as it blows by the soup, it takes some of the heat of the soup with it, so that it cools off faster and you can eat it up.
Heat flow greatly affects the behavior of animals. Warm-blooded animals, like humans and puppies, change their behavior in order to try and maintain a constant internal body temperature inside their core, called the core temperature. If their core temperature drops by even a few degrees, they lose their ability to function. The core of an apple is the inside part where the seeds are. The core of animals is the inside part, too—deep inside the body and away from the surface of the skin. The core is not inside the hands, feet, arms, legs, or limbs, or anywhere near the skin, because the temperature of those parts can change a lot as the body controls blood flow to them in order to protect the core. The core is actually the part inside the torso of the animal—the part of your body between your neck and bottom, where all the internal organs are, like the heart and liver. When warm-blooded animals are placed in a cold environment, they will change their behaviors to try and maintain their core temperature. They will do things like:
- Fluff up their fur or feathers.
- Shorten their limbs.
- Pull their limbs in close to their bodies.
- Seek out any visible sunlight.
- Seek out a warm rock.
- Curl up in a bed of leaves or brush.
- Put on clothes (if they are humans, of course).
- Huddle together.
When animals huddle together, they are reducing the amount of their bodies (the amount of surface area) that is exposed to the open air, and so are reducing heat loss by radiation and convection. A puppy also gains heat by conduction if the puppy snuggled up next to him happens to be warmer than he is. It is nice to have a brother or sister puppy that is also a furnace!
In this mammalian biology science fair project, you will explore how much huddling helps to reduce heat loss. You will create models of puppies out of glass jars, which are not nearly as cute and soft as the real kind, but will let you measure heat loss. How much do you think huddling helps animals stay warm?
Terms and Concepts
- Warm-blooded animals
- Core temperature
- Surface area
- What kinds of objects experience heat flow?
- When do objects experience heat flow?
- What are the types of heat flow and how do they differ?
- Why do animals change their behavior in response to heat flow?
- What are some of the ways animals change their behavior when they are cold? Can you think of ways they might change their behavior when they are hot?
These sources describe ways in which animals change their behavior in cold weather:
- ScienceMadeSimple.com. (1995). How Do Animals Spend the Winter?. Retrieved June 11, 2009.
- Ward, P. (2001). Cool Antarctica. Retrieved June 12, 2009.
This source describes the three methods of heat transfer (conduction, convection, and radiation):
- Watson, D. (2004). Energy, Heat Flow, and Life. Retrieved June 11, 2009.
For help creating graphs, try this website:
- National Center for Education Statistics. (n.d.). Create a Graph. Retrieved June 2, 2009.
Materials and Equipment
- Glass jars or bottles, like canning jars, same size and shape, with lids (3). They need to safely withstand being in boiling water.
- Use jars whose lids do not stick out further than the glass sides of the jars. This is because when the jars are touching each other, you want their glass sides to be touching, and if their lids are bumping then this will not happen.
- If using canning jars, you will need rings for the lids.
- Laboratory or candy thermometers, same size (3); these are available from an online supplier such as
Carolina Biological catalog #745390.
- Must have a range of at least 93°C (200°F)
- Large soup pot, water bath canner, or Dutch oven; should be big enough to hold three jars simultaneously
- Measuring cups, liquid
- Oven mitts (2)
- Graph paper with lines that are 10 mm, or 1 cm, apart; available from office or school supply stores or you can print free online graph paper with lines that are 10 mm apart.
- Lab notebook
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Important Notes Before You Begin:
You will be testing heat loss under the following conditions:
- One puppy alone (with no huddling companions): modeled by a single jar of heated water.
- Two puppies huddling together: modeled by two jars of heated water, touching each other's glass sides.
- Two puppies not huddling: modeled by two jars of heated water, separated by 3 centimeters (cm) on a sheet of graph paper.
- Three puppies huddling together: modeled by three jars of heated water, touching each other's glass sides to form a triangle.
- Three puppies not huddling: modeled by three jars of heated water, separated by 3 cm on a sheet of graph paper.
Preparing Your Puppy Models and Water Bath
- Make a data table in your lab notebook for each of the four configurations, like Table 1 below:
|Time (min)||Trial 1 (°C)||Trial 2 (°C)||Trial 3 (°C)||Average (°C)|
Using a hammer and a nail, carefully make a hole in the center of each lid, just big enough for the thermometer to fit through.
- Ask your parents about a good place to pound the nail, so that you do not damage any table tops or other surfaces.
- When you make the hole, carefully check if it is wide enough to put the thermometer through. Do not force the thermometer through the hole because this could damage the thermometer!
- If needed, slightly adjust the hole (using the nail) so that the thermometer's stem sticks straight, vertically down in the jar, as shown in Figure 2, below. Remember, you want to measure the core temperature of the jar.
Figure 2. Make sure the thermometer's stem sticks straight, vertically down into the jar.
Fill the jars about three-fourths full with equal amounts of the same-temperature tap water, as shown in Figure 3, below.
- Some jars have lines marked on the side that you can use as a guide when filling the jars.
- If your jars do not have lines, then you will need to use measuring cups to make sure you put the same amount of water in each jar.
- Write down in your lab notebook how much water you put in each jar, or what line you used as a guide.
- Put the lids on the jars. Each jar will represent one puppy.
Figure 3. Fill the three jars about three-fourths full with the same-temperature water, as shown here.
Testing Your Puppy Models
- Reset the timer.
Fill the large soup pot, canner, or Dutch oven with enough water so that when all three jars are in the pot, the water level within the jars equals the water level outside of the jars (in the pot). Take the jars out after filling the pot.
- If the pot is not large enough to do this, just fill the pot with as much water as is safe to boil. If you are not sure how much this is, ask for advice from the adult who will be supervising you while you use the stove.
- Put the soup pot on the stove and put a 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, as shown in Figure 4, below.
Figure 4. After filling the pot, put one jar inside of it, and put the thermometer inside the jar.
- Turn on the stove to medium-high.
- When the temperature of the water inside the jar reaches 88°C (190°F), turn off the stove.
- Immediately remove the jar from the water bath with the oven mitts and dry the jar quickly on a towel.
- Immediately start the timer and take your first measurement of the water temperature inside the jar. Enter this measurement into the correct data table for time equals 0.
Continue taking water temperature measurements every 2 min. for at least 10 min.
- Enter your temperature measurements into the correct data table.
- Feel free to take more-frequent temperature measurements.
- Feel free to take temperature measurements for a period of time longer than 10 minutes.
- The larger the jar, the greater the amount of water, and the longer it will take for the jar to cool off.
- Empty the water out of your jar and allow it to come to near room temperature.
- Repeat steps 1–10 two more times for one jar, so that you have a total of three trials. By repeating the experiment three times, you will ensure your results are accurate and repeatable.
Repeat steps 1–10 three times for two touching jars (as shown in Figure 5, below), three times for two jars separated by 3 cm, three times for three touching jars, and three times for three jars separated by 3 cm.
- For the two jars separated trials, have each jar separated by 3 cm. You can use the graph paper to help you figure out where to place the jars.
- For the three jars touching trials, be sure to arrange the jars so that each jar is touching two other jars, forming a triangle, as shown in Figure 6, below.
For the three jars separated trials, also arrange the jars in a triangle.
- Have each jar separated from the two others by 3 cm.
- You can use graph paper to help you figure out where to place the jars, or mark up a piece of graph paper before starting the trial, so that you know where you will be placing each one when the jars come out of the water bath.
- Be sure to put a thermometer inside each jar that you test.
Figure 5. Make sure the two jars are touching along their glass slides when you test the two jars touching, as shown here.
Figure 6. When you test three touching jars, arrange them in a triangle, with their glass sides touching, as shown here.
Analyzing Your Data Tables
- For each data table, calculate the average temperature at each time increment (from the three trials) and enter your calculations in the last column of the data table.
- Create a new data table, like Table 2 below, by entering the averages from the other data tables at each of the time increments.
|Time (min)||One Jar||Two Jars Touching||Two Jars Separated||Three Jars Touching||Three Jars Separated|
Make a line graph that plots the time (in min) on the x-axis and the average temperature (°C) on the y-axis.
- If you put all your line graphs on the same plot, it will be easier to compare them.
Use a different symbol or a different-colored line for each condition.
- For example, you could make the line color for the one-jar results blue, and give them circle symbols for each data point, or make the line color for the two jars touching results green, and give them square symbols for each data point.
- You can make the plots by hand, use a spreadsheet program, or use a website like Create a Graph to make the graph on the computer and print it.
- Looking at the line graph, which configuration of jars reduced heat loss the most (had the highest temperatures)? Which configuration reduced heat loss the least (had the lowest temperatures)?
For each time increment, calculate how much huddling or having other jars nearby reduced heat loss compared to having one jar alone. Do this by using Equation 1, below, to calculate the following comparisons:
- The heat loss for one jar alone compared to two jars touching
- The heat loss for one jar alone compared to two jars separated
- The heat loss for one jar alone compared to three jars touching
The heat loss for one jar alone compared to three jars separated
Equation 1:Heat loss = Average temperature for two or three jars - Average temperature for one jar alone
- For example, if the average temperature at 4 min for one jar equals 83.6°C and the average temperature for two jars touching at 4 min equals 84.1°C, then the heat loss of having one jar alone compared to two jars touching is 0.5°C, since 84.1°C - 83.6°C = 0.5°C.
- Enter your calculations in a data table like Table 3 below.
|Time (min)||Two Jars Touching||Two Jars Separated||Three Jars Touching||Three Jars Separated|
Make a line graph that plots the time on the x-axis and the heat loss on the y-axis.
- If you put all your line graphs on the same plot, it will be easier to compare them.
Analyze your line graph from step 6 and try to draw some conclusions about your data.
- How much heat did one jar alone lose compared to two jars touching, two jars separated, three jars touching, and three jars separated?
- Which configuration prevented the greatest amount of heat loss compared to one jar alone?
- At what time was the heat loss for one jar alone the greatest compared to the other configurations?
- Did more jars huddling together (three instead of two) reduce heat loss more (was three better than two)? If so, how much better was it?
- At any time, was there an advantage to having jars touching, even if they were not huddling?
- Overall, what do your results tell you about how and why puppies huddle to keep warm?
Ask an Expert
- Investigate how adding one or two more huddling puppies (i.e., jars) to the experiment affects heat loss. Can you predict how adding another puppy will affect heat loss?
- Add fur or fat to the outside of your puppy models to see how that affects heat loss.
- Compare large and small jars of the same shape. Which ones retain heat better? Hint: Look at the surface-area-to-volume ratio for each jar.
- Study increased heat loss by convection by blowing a fan on the huddling puppy models and comparing the data to heat loss without the use of a fan.
- Model the behavior of huddling Emperor penguins who trade off positions, so that one penguin does not get stuck on the outside of the huddling group for too long. Place one jar in the middle of three or four jars and evaluate its heat loss for a few minutes, then switch the middle jar to an outside position and move one of the outside jars to the middle. Compare the heat loss of a jar that is switched from the outside to the middle with one that remains on the outside the whole time.
- How does the core temperature of a puppy model compare to its external, or surface temperature? You could investigate the surface temperature by using an infrared thermometer temperature gun, which is available through online suppliers such as Amazon.com.
If you like this project, you might enjoy exploring these related careers: