The Physical Effect of Heat upon Bodies
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-238
2025-11-20
17
There are two main results that may come from applying heat to a body. One is a change in its volume, and the other is a change in its physical condition.
Demonstrations. – Make a shown in Fig. 1, as follows: Set two upright posts in a baseboard. Bore in each post, near the top, a hole large enough to take a brass wire 1/8 in. in diameter. Fasten one end of the wire to one post by a screw in the top and let the wire pass loosely through the other post. Connect a battery and electric bell with the wire, and let the other end of the circuit be connected with a thin brass spring just beyond the movable end of the wire. Adjust the spring carefully and bring the flame of a Bunsen burner against the wire. The heat will expand the wire, which will make contact with the spring, when the electrical circuit will be completed and the bell will ring. Remove the flame; the wire will contract, the contact will be broken, and the bell will stop ringing.
Fit to the mouth of a test tube a rubber stopper with a single hole. Thrust a piece of glass tubing, about 30 cm. long, through the stopper. Fill the test tube with water and push in the stopper until the water stands at some point, as A (Fig. 2). Take the tube by the end
and lower the test tube into a beaker of hot water. The first effect is that the water in the small tube will drop to B. What is the cause of this? The second effect is that the water will then begin to rise and will finally run over the top C. Why?
Empty the test tube, and let it become dry and cool. Introduce a short column of water into the middle of the small tube, hold it in a horizontal position, and push in the stopper as before. Clasp the test tube in the hand and watch the position of the water index.
There are many practical uses of the expansion of solids when heated. A tire for a wooden wagon wheel is made of a size slightly smaller than the circumference of the wheel; to put it on, the tire is heated, driven into place on the wheel, and on cooling becomes small enough to be held very firmly. Large guns are built up by forcing heated steel rings over a steel core and letting them shrink on, after which the guns are bored out and rifled.
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