# Evaporation of perspiration

• physics1234
In summary, when jogging at a rate that uses 400 kcal/h above your BMR for 30 minutes, the primary mechanism for eliminating the energy is through the evaporation of perspiration. This results in a loss of water, with the amount being equivalent to the maximum fat-burning energy output. The metabolism of 1 gram of fat generates approximately 9.2 kcal of energy and produces approximately 1 gram of water. Therefore, a fraction of your water needs will be provided by fat metabolism. To determine the exact amount, you will need to use the formula Q=mL, where Q is the total energy burned during the exercise and L is the latent heat of vaporization of water expressed in calories. From there, you can

#### physics1234

When you jog, most of the food energy you burn above your basal metabolic rate (BMR) ends up as internal energy that would raise your body temperature if it were not eliminated. The evaporation of perspiration is the primary mechanism for eliminating this energy. Determine the amount of water you lose to evaporation when running for 30 minutes at a rate that uses 400 kcal/h above your BMR. (That amount is often considered to by the "maximum fat-burning" energy output.) The metabolism of 1 gram of fat generates approximately 9.2 kcal of energy and produces approximately 1 gram of water. (The hydrogen atoms in the fat molecule are transferred to oxygen to form water.) What fraction of your need for water will be provided by fat metabolism?

Well, I found that the latent heat of vaporization of water is 2.5 x 10^6 J/kg
and that I need to use the formula Q=mL but I don't know where to start.

Well, how much total energy do you burn doing the exercise? How much fat is required to produce the energy?

Can you supply the final two steps...

BTW, you'll need the latent heat of vaporization expressed in calories rather than joules.

I would like to clarify a few things before providing a response. First, it is important to note that the amount of water lost through perspiration during exercise can vary depending on factors such as intensity of exercise, environmental conditions, and individual factors. Therefore, the calculation provided in the content may not be accurate for everyone.

That being said, let's assume that the given information is applicable for an average person. The first step would be to calculate the total amount of energy burned during the 30 minutes of jogging at a rate of 400 kcal/h above the BMR. This would be equivalent to 400 kcal/h x 0.5 h = 200 kcal.

Next, we can use the given information that 1 gram of fat metabolism produces approximately 1 gram of water. Therefore, the amount of fat burned during the 30 minutes of jogging would be equivalent to 200 kcal/9.2 kcal/g = 21.74 grams.

Now, to determine the amount of water lost through perspiration, we can use the formula Q = mL, where Q is the energy released during the metabolism of fat (200 kcal), m is the mass of water (in kg), and L is the latent heat of vaporization of water (2.5 x 10^6 J/kg). Rearranging the formula, we get m = Q/L.

Substituting the values, we get m = 200 kcal / (2.5 x 10^6 J/kg) = 8 x 10^-5 kg. This is equivalent to 0.08 grams of water.

Therefore, the fraction of water provided by fat metabolism would be 0.08 grams / 21.74 grams = 0.0037 or 0.37%.

This calculation shows that a very small fraction of our water needs are met through fat metabolism during exercise. It is important to note that this is a simplified calculation and does not take into account other sources of water loss, such as breathing and sweat losses from other parts of the body. Additionally, it is important to maintain proper hydration during exercise to replace the water lost through perspiration.

## 1. What is evaporation of perspiration?

Evaporation of perspiration is the process by which moisture from the skin is converted into water vapor and released into the air. This is a natural cooling mechanism of the body to regulate its temperature.

## 2. How does evaporation of perspiration cool the body?

When sweat evaporates from the skin's surface, it absorbs heat from the body, causing a cooling effect. This is because the energy required for water to change from a liquid to a gas comes from the surrounding environment, in this case, the body's heat.

## 3. Does evaporation of perspiration always occur?

No, evaporation of perspiration only occurs when the surrounding environment has a lower vapor pressure than the sweat on the skin's surface. This means that humidity levels and temperature play a crucial role in whether or not sweat will evaporate.

## 4. Can evaporation of perspiration be harmful to the body?

In normal conditions, evaporation of perspiration is a beneficial process for the body. However, if the body is exposed to extreme heat and humidity, excessive sweating can lead to dehydration and electrolyte imbalances, which can be harmful. It is essential to stay hydrated and take breaks in hot environments to avoid these risks.

## 5. How can evaporation of perspiration be measured?

Evaporation of perspiration can be measured using a variety of methods, including gravimetric, hygrometric, and psychrometric techniques. These methods involve measuring changes in weight, humidity, and temperature, respectively, to determine the rate of evaporation. More advanced techniques, such as thermal imaging, can also be used to visualize sweat evaporation on the skin's surface.