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Keeping food hot
Introduction
Meals on Wheels supply meals to people in the community who find it difficult
to cook for themselves. It is important to keep the food as hot as possible
during the journey from kitchen to customer. The food and drinks are packed
in containers.

This investigation looks at which containers keep food the hottest. It is
assumed for this practical that the containers are made of glass. Different
insulating materials are wrapped around them to keep the food warm.

Most food has a high water content. Hot water is therefore used in this study
to simulate the hot food or drink in the containers.

What you need

   Five glass beakers (identical)
   Water heated to 45C
   Five temperature sensors (or only one, if you do the experiments
separately)
   Newspaper
   Bubble wrap
   Kitchen foil
   Corrugated cardboard
   Datalogger

What you do
1. Measure the thickness of each insulating material.
2. Cut out a 'jacket' of different insulation for each beaker, including a
separate lid. Make a slit in each lid through which the temperature sensor will
fit.
3. Surround each beaker in a different insulating material, leaving the top
open.
4. Carefully pour hot water into each beaker until it is three-quarters full.
5. Cover each beaker with its lid.
6. Place a temperature sensor in each beaker through the slit in the lid.
7. Start the datalogging software immediately. You can use the 'trigger' option
on the datalogger to start recording in each beaker at the same temperature.
8. Record the temperature for five minutes.
9. Record how the glass beakers were insulated, and the thickness of the
insulation layer, in a table like the one below:

Treatment                          Insulation           Estimated thickness [mm]
1                         Control [no insulation]               0
2                              Newspaper                       0.2
3                             Bubble wrap                      5.0
4                              Kitchen foil                    0.1
5                         Corrugated cardboard                 2.0

What you found
Presenting the results

It is important to present all the results on the same graph. If the experiments
have been done separately, the graphs can be overlayed onto each other.
Some applications allow graphs to be merged together after all the
experiments have been completed.

The graphs below were obtained from the experiment. Graph 1 shows all five
experiments and the temperature inside the room. Graph 2 shows a magnified
section of graph 1.

Meals on Wheels

50                                               50
Temperature (C)
Temperature (C)

40                                               40

30                                               30

20                                               20

10                                               10
0    1         2        3        4
Time (minutes)
Key to graph
Pink line = bubble wrap as insulation
Light blue line = corrugated cardboard as insulation
Green line = kitchen foil as insulation
Red line = newspaper as insulation
Brown line = control [no insulation]
Blue line = room temperature

Graph 2
[Graph 1 magnified and 'smoothed']

Meals on Wheels

45                                            45
Temperature (C)

Temperature (C)
40                                            40

35                                            35

30                                            30

0     1        2         3         4
Time (minutes)

Key to graph

Pink line = bubble wrap as insulation
Light blue line = corrugated cardboard as insulation
Green line = kitchen foil as insulation
Red line = newspaper as insulation
Brown line = control [no insulation]
Blue line = room temperature

Draw your own graphs from data collected in this experiment. The data are
available in several different formats. The format you choose depends on the
software you have available to use, and whether you want to carry out extra
analysis using the datalogging software.
Formats available:

www.scienceonline.co.uk/members/experiments/meals.CSV[suitable for using
directly as a table in Excel]
www.scienceonline.co.uk/members/experiments/meals.SID
www.scienceonline.co.uk/members/experiments/meals1.ISA
www.scienceonline.co.uk/members/experiments/meals2.ISA (smoothed)
www.scienceonline.co.uk/members/experiments/meals3.ISA (zoomed)
www.scienceonline.co.uk/members/experiments/meals.ISD

Analysis of results

1. What is the general trend in the graphical data for all the experiments?
3. Produce a table giving an estimated loss of temperature for each of the
experiments if the length of the experiment is:
a) 5 minutes
b) 10 minutes
c) 1 hour.
4. Does the thickness of the insulating material have any effect on the

Evaluation

1. Explain how you could make the experiment fairer?
2. How could you improve the experiment?
3. Why is it important to have a control experiment?

Extension questions

1. Explain how you would insulate a house to save energy.
2. Why are runners given silvered blankets at the end of races?