The Physics of Drinking Water in Hot Weather

 

I was writing a few hours ago how to manage hot weather here:

“What to do in hot weather”.

https://scientificlogic.blogspot.com/2024/

I mentioned drinking cold water and about using a fan to speed up the heat of evaporation from the sweat. This is much more effective than going into an air condition room.

 I thought I should now explain the physics of how drinking cold water drains away heat and reduces temperature. Later I shall explain the differences between heat and temperature.

Let us go from medicine into physics and a bit into mathematics. Bear with me.

Can we ask how much heat is drained away into the urine by drinking water?

 Let’s say (example) we drink 1 litre (1,000 g) of water at 20 ⁰ C. That is going to warm the urine to be passed out from the body temperature at 37 0 C?

How does this mathematically work out?

Let, M = 1000 g (mass of 1 litre of water)

C = 4.18 Joules / g ⁰ C (specific heat capacity of water)

∆ (Delta T) or Q:  37 – 20 = 17 ⁰ C (change or increase in temperature from cold water into urine temperature)

Amount of heat (Q) required or transferred = (1000 g) x 4.18 Joules / g ⁰ C) x 17 ⁰ C

= 71,000 Joules (17 kilocalories)

We convert Joules into kilocalories by dividing joules by 4.184 as given above.

(1 kcal = 4,184 joules (4.184 Joules or J)

Let us now go into nutrition to determine the number of calories an adult needs per day. This of course can vary based on factors such as age, sex, weight, height, activity level, and overall health. Some of guidelines suggested for daily calorie intake are:

1. Sedentary (little to no exercise): 1,800 to 2,200 kcal (7530 – 9200 J)
2. Moderately active (light exercise/sports 1-3 days/week): 2,000 to 2,400 kcal (8300 – 10,000 J)
3. Active (moderate exercise/sports 3-5 days/week): 2,200 to 2,800 kcal (9200 – 12000 J)
4. Very active (hard exercise/sports 6-7 days a week): 2,400 to 3,000 kcal (10000 – 13000 J)

Let us say (example) we take 2000 kilocalories or “calories” as our adult daily requirements. This means drinking 1 litre of cold water at 20 ⁰ C, will transfer the heat from the blood to warm up the cold water into the freshly passed out urine which is the temperature of the body at 37 0 C.

This would be 17 / 2000 x100 = 0.85 % of the heat from the combustion of food into the urine.

Please note there is a difference between “heat” and “temperature”.  

Let us now change from nutrition into physics again.

  In physics (thermodynamics) they are different aspects of a system. Heat means a form of energy transfer between two systems or between parts of a system. It is the energy that flows from a region of higher temperature to a region of lower temperature. The unit of heat is the joule (J) in the International System of Units (SI).

But when we say “temperature” we mean a measure of the average kinetic energy of the particles in a substance or system such as how hot the body, blood, water or urine. It does not depend on the amount of substance but it's a property of the substance itself. The unit of temperature in the SI system is the Kelvin (K), but can also be expressed in degrees Celsius if it is not exceeding hot like the Sun.

In simpler terms, heat is the energy transferred between systems or within a system due to a temperature difference, while temperature is a measure of the thermal energy of the particles in a system.

 Another way of putting it is, we can say heat is the quantity of thermal energy in a system that can be measured in calories or in joules, whereas temperature is the intensity of heat in that system that is measured in degrees Celsius or in Kelvin

But since they are related, we can transfer the heat energy from one system (say from the body) to another system (say into the urine) to bring down the intensity of the heat which is the temperature of body in a heat stroke.  

This explains how drinking water can cool down the excess heat received by the body in hot weather and drained out into the urine.

Once again, do NOT treat heat stroke medically in hot water by using antipyretic (fever reducing) drugs such as paracetamol. 

Hot weather is an external problem, not an internal body problem. It is outside the control of the body, and we need to use external means to manage it, not use antipyretic (fever-reducing) drugs like aspirin or paracetamol to treat it.

Fever is normally caused by some infection and is an internal problem which may necessities the use of antibiotics and an antipyretic agent to deal with the infection and fever.

 In fact, it may not even be advisable to block the fever in an infection due to a natural attempt by the body to combat the infection by speeding up activities of the phagocytes and other components of the white blood corpuscles, immunoglobulins and other immunological components and responses for faster recovery.

The only exception is when the body’s temperature is critically high into hyperthermia (overheating) when an antipyretic drug may be indicated. Even this can be dealt with by drinking lots of fluid and sponging the head and body. Please do not use drugs the easy way to deal with every internal and external problems in health.  This practice is not good medicine. 

Lim jb