|
 |
Research Assistant Wanted
Brother Gregory wants you to help him find answers to various questions
about energy and energy related subjects. In these investigations he
will ask you a question and give you the tools to find the answer.
You then become his research assistant. You must carry out the experiment,
gather data, analyze your results and give Brother Gregory the answer he seeks.
(Hint: If you run into trouble, ask his mother for help!).
|
|
|
Brother Gregory's Dinner
Brother Gregory was concerned about his spreading waistline.
He felt that he was putting on too much weight and was getting fat.
So he looked closely at what he was eating.
A typical dinner consisted of:
|
Food Eaten |
|
Food Item |
Amount in Grams |
|
Beef |
230 gms |
|
Bacon |
37 gms |
|
Chicken |
158 gms |
|
Beans |
300 gms |
|
Broccoli |
98 gms |
|
Milk |
345 gms |
|
Apple |
500 gms |
The question is, "Was he eating too much food?"
He wants you to find out.
|
|
|
He wants you to do three things;
- you must find out how many calories there are in each of these food items,
- determine the total number of calories in this meal, then
- find out if his meal would have more or less calories
if he substituted pork for the beef, eggs for the cheese
and tea instead of milk.
|
|
|
Tools of the Trade
In order to carry out this investigation you will need to learn how scientists determine the number of calories there are in a sample of a substance.
The piece of equipment they use is called a Calorimeter.
|
|
|
Using the Calorimeter
The Apparatus
The Calorimeter consists of a container inside a container.
The sample is placed inside the inner container, and sometimes
pure oxygen gas is also added. This container is then placed
inside the outer container. Water is also placed in the outer
container so that it surrounds the inner container.
A thermometer is placed into the water.
|
|
|
|
The Measurement
- A small amount of the sample under investigation is weighed,
the weight written down and the sample placed into the inner container.
- The inner container is sealed, placed in the water,
and the whole apparatus allowed to equilibrate.
- The initial starting temperature of the water in the outer container
is written down as the first data point.
- The sample is burnt in the air (or oxygen) and energy is released.
- The energy from burning the food moves into the water surrounding
the inner container and the temperature of the water goes up.
- The increase in temperature is written down.
|
|
|
Calculating the Results
The investigator now has four pieces of data:
T1 = The starting temperature of the water.
T2 = The final temperature of the water.
V = The volume of water in the apparatus.
S = The weight of sample (in grams).
|
|
|
Definition
A calorie is the amount of energy needed to raise the temperature of one gram of water from 14.5 to 15.5 degrees centigrade.
|
|
|
Calculation
The number of calories of energy in the sample can be calculated
from the following formula:
Number of calories = V x (T2-T1)
Knowing the total number of calories of energy given off by
burning the sample, and knowing the number of grams of sample
that were burnt, the following formula gives the "calorific value" of the sample:
Calorific Value = Number of Calories / grams of sample
or a combined formula for the calorific value of the sample would be:
Calorific Value = (V x (T2-T1)) / S
|
Use the Calorimeter
