from Come Fly With Me – Exploring Science through aviation and aerospace concepts.
GROUP SIZE: Small
TIME: 2-60 minute periods
TYPE OF ACTIVITY: Student Investigation
TEACHING STRATEGY: Expository and Guided Discovery
CONCEPTS: Calorie Combustion Heat Energy
SKILLS: Construction Experimentation Interpreting Data
Objectives: To understand that the energy produced by food may be measured by determining the heat produced by combustion of that food; to relate that concept to the energy produced during metabolism; to relate the above to the amount of calories needed by an astronaut in a weightless environment.
Materials: Can; 250ml beaker; thermometer; graduated cylinder; centigram balance; wire screen; cork; needle; food (peanuts, pecans, sugar cubes, vegetable oil or hard cooked egg white)
Teacher Background Information:
The energy produced by the metabolism of food is precisely the same as that produced by burning the food (metabolism and burning are both oxidation processes). The heat produced by this process is measured in calories or BTU’s. In most scientific work, the preferred unit is the calorie. A calorie is the amount of heat needed to raise the temperature of 1 ml (lg) of water 1 degree Celsius. The calories we talk about when discussing food are actually kilocalories (the energy required to heat 1000ml of water 1 degree Celsius).
For very precise work, food is placed in a device called a bomb and lowered into a tank of water. The food is mixed with an exact amount of an oxidizer and all of the food is burned. Every bit of heat is measured by gently stirring the water and recording the temperature change. In this activity, even though not a precise experiment, a careful student should be able to realize results within 10% or so of actual values.
Prepare the calorimeter assembly as shown in the illustration. Punch the holes around the bottom of the can before the bottom is removed. The can will act as a chimney to concentrate the heat on the bottom of the beaker of water so it should be about the same diameter as the beaker. Place the needle into the cork and attach the food to be tested to the other end of the needle.
Measure the mass of the food to be tested on a centigram balance.
Measure the mass of the water. (It will be easier if the students try for amounts like 100g or 150g.)
Measure the temperature of the water. Ignite the food and quickly place the chimney over the food and the screen and beaker on top of the can. Continuously stir the water gently. As soon as the food has stopped burning, record the temperature of the water again. Keep recording the temperature until it stops climbing. It may continue to climb for a few moments after the food ceases to burn.
- Compute the Kilocalories/Gram for the food burned.
- KCal = (change in temperature)x(grams of water) / ((grams of food) x 1000)
Try the experiment again or compare with others who used the same food. Several trials make for better accuracy. Try the experiment with other foods.
Discuss what some of the special considerations for caloric intake might be for an astronaut in space. Would the requirements be the same in the weightlessness of space compared to training back on Earth? Why or why not?
Try the “Run To The Moon” activity next. Keep your calculator handy!!
If you use vegetable fats during your test you may find them difficult to handle. You can make them easier to burn by soaking a little cotton or fiberglass with the oil first then igniting the cotton. Burn a measured amount of cotton first under some water and compute the caloric value of the cotton. Use the same amount of cotton soaked in fat or oil and subtract the first value for the cotton alone from your second results to compute the calories in the fat alone. A sugar cube will burn a little easier if you rub a few ashes on it first.
For all practical purposes, all fats give off the same amount of calories and for all carbohydrates the caloric value is the same. In the experiments above, the vegetable oil would be a fat and the sugar cube would be a carbohydrate. The caloric value of protein can be found by subtracting the percentage values for fat and carbohydrate in a food from the total. what is left is the value for protein. Have the students compute the average values for fat and carbohydrates from their data and then compute the values for protein using the following chart.
Adapted from educational materials available from NASA Spacemobile program
PEANUT CALORIMETER CHART
|FOOD||KCal/Q||%H2O||% Protein||% Fat||%Carbohydrates|
|Cooking oil, Crisco||9.00||..||..||100.0||..|
|Egg, white boiled||.57||..||12.3||.6||..|
Teacher Note: The values for Fats, Protein and Carbohydrate follow. You may wish to cut this off before reproducing this for you students if you want them to do their own computations.
- Fats 9
- Protein 4
- Carbohydrate 4