Firewood Heat Experiment

Complexity level:	4
Project cost ($):	20
Time required:	1 hour to prepare, 1 hour for experiment
Material availability:	Easily found
Safety concerns:	Fire hazard. Parents should supervise the experiment and handle all flammable materials. This experiment should be undertaken only under the watchful eye of an adult. A fire extinguisher should be kept on hand at all times for safety and no flammable gases/materials should be present in the vicinity of the experiment.

Hypothesis

The hardwoods are denser and therefore produce more heat compared to soft wood.

Overview

Firewood

There are many types of firewood available for use in cooking or heating. The choice of wood to be used depends the purpose for which it is used, and weather conditions. Your choice of wood may vary if it is used for outdoor cooking, barbecques, fire places or campfire. Some of the things we need to know about firewood are listed below.
Use only dry or seasoned firewood for burning. Wet or recently cut firewood will contain water moisture. They will burn at lower temperatures and release more smoke.

The amount of heat from a burning wood is measured in British Thermal Units (BTUs). Hard woods have higher BTUs and therefore are more effective as firewood, as compared to soft woods which have lower BTUs
Hard woods have a very high density. The amount of potential thermal energy stored per unit volume of hardwood is high and therefore hardwoods have higher BTUs. These woods are difficult to ignite but once they start burning, they will burn for a longer period of time, giving out less intense heat.

Soft woods have a lower density. The amount of potential thermal energy stored per unit volume of hardwood is low and therefore soft woods have lower BTUs. These woods are easy to ignite but the heat is low and they do not burn for very long.

Scientific Terms

British Thermal Units (BTUs), density, thermal energy

Materials

The materials required for this experiment:

3 pieces of oak wood (each cut to approximately 10cm x 3cm x 1cm)
3 pieces of maple wood (each cut to approximately 10cm x 3cm x 1cm)
3 pieces of cedar wood (each cut to approximately 10cm x 3cm x 1cm)
3 pieces of pine wood (each cut to approximately 10cm x 3cm x 1cm)
A 500ml beaker
A thermometer
A lighter
A tripod stand for the beaker
2 liters of tap water
A stop watch
A ceramic tile (250mm x 250mm) or 2 bricks
A small bottle of kerosene

Procedure

For this experiment, the independent variable is the type of wood used. The dependent variable is the temperature of the water. This is determined by measuring the temperature using a thermometer. The constants (control variables) are the amount of firewood used, the amount of water used, the formation of the 4 wood pieces and the height of the beaker from the firewood.
Fill the beaker with 300ml of water. Measure the temperature of the water then put it aside
Place the ceramic tile or bricks on the table. Be sure to protect the table with a large baking tray or aluminum foil. The 4 pieces of oak wood are arranged on the tiles in a tent-like or grid-like formation. Ensure that the tiles are arranged in a manner that prevents the burning wood from touching the table. Sprinkle a small measured amount of kerosene (eg. 10 ml) on the wood and using the lighter, start a fire.
The wood is allowed to burn for 1 minute, then the tripod stand is placed over the fire
Place the beaker on the tripod stand and record the temperature of the water every minute for 5 minutes. All the readings are recorded in the table below.

Repeat procedures 2 to 5 using the maple wood, cedar wood and pinewood. All of the measurements are recorded in the table given below.

Results

The results show that oak wood and maple wood causes the temperature of the water in the beaker to increase faster as compared to cedar wood and pinewood.
heat experiment results
Oak wood and maple wood are hard woods whereas cedar wood and pine wood are soft woods.

Use the graph below to plot the results.

Conclusion

The hypothesis that hardwoods produce more heat as compared to soft wood is proven to be true. The hardwood gave out more heat when burned, thus driving up the temperature of the water higher than in the case of softwoods. In addition, they burned for a longer period of time as compared to the soft wood.

With the rising prices of electrical heating, oil and gas, the use of firewood for burning is an alternative source of cheaper energy. However overuse of firewood for burning will lead to pollution and deforestation. In addition, the carbon dioxide gases released into the atmosphere from an open fire contribute to global warming and ocean acidification.

Also consider

The experiment can be repeated by measuring the amount of time taken for the wood to burn out.

Try to repeat the experiment using an infrared thermometer to measure the temperature of the fire directly.

Try using a different formation of the wood pieces for burning. Would the results be different?

References

What is the best firewood? - http://www.firepit-and-grilling-guru.com/best-firewood.html
Firewood and cordwood - http://www.donnan.com/firewood.htm

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