Alexander Graham Bell National Historic Site of Canada
Activities
Bell's After Dinner Experiments
Simple experiments can lead to new discoveries about the world around us, and through experiments, basic scientific principles can be understood more readily. We observe a phenomenon and seek to discover why it occurs.
As an enthusiastic proponent of the Montessori method of teaching, Alexander Graham Bell felt that the concept of learning by doing was a most important one. And as a teacher of the deaf, and a father and grandfather, he came to spend a great deal of time with children. He did not think that children should have general principles of science explained to them and then accepted upon authority. He was devoted to providing the means through which children could learn to reason for themselves.
Included with each experiment is a simple explanation as well as the scientific principle involved. Accompanying each experiment is a description of situations in which Bell used the experiment. You can imagine the wonderment in his granddaughter's eyes when he invited her to a luncheon of cooked balloons, or the perplexity of the little boy who was repeatedly instructed by Bell to fill a bottle with hot water only to return to find it was no longer full.
It is recommended, of course, that the parent, teacher or assisting adult do those parts of the experiments which involve the use of matches or hot water, while the children observe. Enjoy!
1. INVERTED GLASS OF WATER
Materials:
1 drinking tumbler, glass or plastic.
1 piece of construction or blotter paper (at least ½ in. bigger than diameter of glass)
Enough water to fill glass
Empty container (e.g. dishpan)
Method:
Fill glass of water to brim. Place paper over mouth of tumbler. Hold paper in place with hand and turn glass upside-down quickly. Remove hand holding paper.
Desired Results:
Paper will remain in place and water will remain in inverted glass.
Scientific Principle:
At sea level the atmospheric pressure is 101.3 Kilopascals (Newtons per meter squared) or 14.7 lbs./sq.in. This pressure is felt in all directions and on everything. In this experiment, when the glass is filled with water, the air is replaced by the water. Since there are only about 200 grams or about ½lb of pressure exerted by the water inside the glass, the atmospheric pressure outside the glass is much greater and therefore the paper remains in place. (14.7 - 0.5 lbs. equals 14.2 lbs. pressure on paper).
Bell Connection:
Bell recorded this experiment in Beinn Bhreagh Recorder on Jan. 19, 1912 as being shown to Mrs. Bell and Mr. and Mrs. Fairchild.
Presentation Suggestions:
Perform experiment over a container to avoid spilling water everywhere.
2. EGG INTO THE BOTTLE
Materials:
One peeled hard-boiled egg.
One narrow-necked glass milk bottle
Scrap of paper
Matches
Method:
Light scrap of paper and drop into bottle. Before fire goes out set egg firmly on top of bottle.
Desired Results:
Fire goes out and egg will be sucked into bottle with loud pop.
Simple Explanation:
The fire burns up the oxygen inside the bottle, creating less air pressure inside than outside. The greater air pressure outside the bottle forces the egg into the bottle.
Scientific Principle:
When a gas is heated its volume increases (Charles' Law, Ideal Gas Law). When the egg is placed on top of the bottle, sealing the bottle, the fire consumes all the oxygen and goes out. Thus the temperature in the bottle decreases, reducing the pressure (Boyle's Law) and creating a vacuum. Also the air pressure outside the bottle (101.3 kilopascals or 14.7 lbs./sq.in.) helps to force the egg into the bottle.
Bell Connection:
In the movie Dr. Bell at Baddeck Bell's daughter, Elsie Grosvenor, talks about her father having shown this experiment to her.
Presentation Suggestions:
Not recommended for child participation because of fire but child may place egg on top of bottle. Bottle MUST be dry inside. Egg must be placed on bottle before fire goes out.
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