In the magical world created by J.R.R. Tolkien, hobbits are famous for two things: being small and having big appetites. Even though hobbits are less than half the size of humans, they eat seven times a day! This might seem like just a fun fact about these charming, hairy-footed creatures, but it actually connects to how much food they would need to survive according to the laws of nature.
All warm-blooded animals, including hobbits, have similar basic needs when it comes to energy. This means that the cells inside a hobbit would need about the same amount of energy as those inside other small mammals or even larger animals. Scientists use a rule called Kleiber’s law to predict how much food warm-blooded creatures need. This rule says that an animal’s energy requirement is related to its mass, but not in a straightforward way. Instead, it scales to the ¾ power of its mass.
For example, an elephant is 100,000 times heavier than a mouse, but it doesn’t need to eat 100,000 times more food. It only needs about 6,000 times more. This means smaller animals have to eat more food relative to their size compared to larger animals. The reason for this scaling is not entirely clear, but part of it is explained by the square-cube law. This law tells us that as an animal gets bigger, its volume increases faster than its surface area. Larger animals have less surface area compared to their volume, so they lose heat more slowly and need less energy per kilogram to stay warm.
Even though we don’t know all the reasons why Kleiber’s law works, we can use it to figure out how much a hobbit would need to eat. Based on some calculations, a hobbit weighs about 16 kilograms. According to Kleiber’s law, a hobbit would need around 500 calories a day, while an average human weighing 82 kilograms would need about 1800 calories. However, the food a human eats is only 0.5 percent of their total weight, while a hobbit’s food intake would be 0.8 percent of their weight.
So, while most humans can get by with three meals and a snack each day, hobbits need more chances to eat. They would need four full meals and three snacks to stay happy and full. This explains why hobbits are always ready for another meal!
Imagine you are a hobbit planning your meals for the day. Based on the information that hobbits eat seven times a day, design a meal plan that includes four full meals and three snacks. Consider what types of food would provide the necessary energy and nutrients for a hobbit. Share your meal plan with the class and explain your choices.
Using Kleiber’s law, calculate how much energy you would need if you were a hobbit. First, find your weight in kilograms and compare it to the average hobbit weight of 16 kilograms. Then, use the scaling factor to estimate your daily calorie needs as a hobbit. Discuss how your results compare to your actual energy needs as a human.
Research the eating habits of humans and compare them to those of hobbits. Create a Venn diagram to illustrate the similarities and differences. Consider factors such as meal frequency, portion sizes, and types of food consumed. Present your findings to the class.
Conduct a simple experiment to understand the square-cube law. Use clay or playdough to create models of animals of different sizes. Measure their surface area and volume, and discuss how these measurements relate to energy needs. Explain how this law helps us understand why smaller animals, like hobbits, need more food relative to their size.
Organize a role-play activity where you and your classmates simulate a hobbit feast. Assign roles such as hobbits, cooks, and storytellers. Prepare a script that includes discussions about the importance of each meal and the energy it provides. Perform the role-play for the class, highlighting the cultural and biological reasons for hobbits’ eating habits.
**Sanitized Transcript:**
Hi, this is David from MinuteEarth. In Tolkien’s fantasy world, hobbits are known for two seemingly contradictory things: being small and being hungry. The average hobbit is less than half the size of a human yet eats seven times a day. While this may seem like just another delightful detail about our favorite hairy-footed characters, it’s actually related to how much food the laws of nature predict a hobbit would need to survive.
Since the basic internal workings of all warm-blooded animals are quite similar, there’s no reason to believe that the cells inside a hobbit would have drastically different energetic needs than those inside a small mammal or a larger animal. We can take the rule we use to predict how much food warm-blooded creatures need to eat and apply it to hobbits as well. This rule, known as Kleiber’s law, states that an animal’s energy requirement scales in proportion to the ¾ power of its mass. For example, an elephant that’s 100,000 times more massive than a mouse doesn’t have to eat 100,000 times as much; it only needs to eat about 6,000 times more.
This means that a small animal has to eat a larger amount relative to its body size than a large animal does. The reason energy needs scale at this particular proportional power is still not completely clear. The square-cube law helps explain part of it. It tells us that, because volume is proportional to the cube of the length while area is only proportional to the square of the length, as something gets bigger, its volume increases faster than its surface area. Larger animals have significantly less surface area relative to their volume than smaller animals, so they lose heat less quickly and therefore need less energy per kilogram to maintain their body temperature. If that were the only factor, we would predict that energy consumption would scale to the power of ⅔, but for most animals, it seems to scale to the power of ¾. This is likely due to a few other differences that affect the scaling between large and small animals, such as their proportion of energy-demanding tissues or the efficiency of their circulatory systems.
Even if we don’t know exactly why Kleiber’s law works, we can use it to predict how much a hobbit would need to eat. Based on some detailed calculations, we estimated a hobbit’s weight at about 16 kilograms. According to the law, a hobbit would need to eat around 500 calories a day, while an average 82-kilogram human would need about 1800 calories a day to survive. However, the amount of food a human eats represents just 0.5 percent of their total mass, whereas the amount of food a hobbit would need to eat would represent 0.8 percent of their total mass.
So while most humans can meet their daily needs with three meals and a snack, a hobbit would need a few extra opportunities to eat; four full (hobbit-sized) meals and three snacks would be just about enough to keep them satisfied.
Energy – The ability to do work or cause change – In physics class, we learned that energy can be transferred from one object to another.
Mass – The amount of matter in an object – The mass of an object does not change, even if it is moved to a different planet.
Calories – A unit of energy used to measure the amount of energy food provides – Our biology teacher explained that we need calories from food to fuel our bodies.
Surface – The outermost layer or boundary of an object – The surface of the pond was smooth and reflected the sunlight beautifully.
Volume – The amount of space an object or substance occupies – We calculated the volume of the box to determine how much it could hold.
Animals – Living organisms that can move and respond to their environment – In biology, we studied how different animals adapt to their habitats.
Law – A statement based on repeated experimental observations that describes an aspect of the world – Newton’s first law of motion states that an object at rest will stay at rest unless acted upon by a force.
Needs – Basic requirements for survival, such as food, water, and shelter – All living organisms have basic needs that must be met to survive.
Food – Substances consumed to provide nutritional support for an organism – Plants produce their own food through the process of photosynthesis.
Habits – Regular patterns of behavior or practices – Animals develop habits that help them find food and avoid predators.
