Question

The situations:

A) Normal human body temperature is 37°C. Room temperature is more like 25°C. So unless it's really hot out, there is always a temperature difference between your body and its surroundings. What's going on?

B) You get too cold, and need to warm up. What happens?

C) You get too warm, and need to cool down. What happens?

D) Now answer parts A, B, and C for the cold-blooded animal (e.g. reptile) of your choice!

For each of these situations, discuss the following questions with your group:

1) What's happening? Explain what's going on qualitatively, and feel free to bring in outside knowledge.

2) What object or set of objects is the most useful for you to define as "the system"? (There's no one correct answer to this! This is a choice you can make.)

3) During the process described, what is the change in the total energy of the system? (Positive, negative, or zero?)

4) Same question as 3, for the chemical energy in the system.

5) Same question as 3 for the thermal energy in the system.

6) Does any energy enter or leave the system? If so, by what process (heat, work, etc.)?

Answer 1

a) In our body there is a constant heat generation due to metabolism. As our body is a heat source it needs a sink to maintain a body temperature. Thus if the environment is at lower temperature it acts as a heat sink.

b) We feel cold when rate of heat going out of our body is greater than produced by our metabolism. Thus if the environment temperature is too low we feel cold. If we wrap ourselves with a blanket the rate of heat loss decreases.

c) When the temperature of environment is not sufficiently low we start feeling warm because we can no longer loose heat to environment. Thus if the environment temperature even comes nearby to 33-34 we start feeling uncomfortable.

d) Cold blooded animals do not rely on metabolism. They bask in sun when it's cold and hide in shade when it's hot. That's why they generally have holes inside earth.

2) You can define the body as a system.

3) Considering temperature to be constant the total energy inside human body is decreasing. Because our food is giving energy which is getting lost to environment.

4) Chemical energy stored in glucose is definitely decreasing due to metabolism.

5) If in steady state the thermal energy is not changing for our body because the energy we loose to environment we get from food.