by Tony Carlini Sr.
Mr. Carlini's lengthy article on color, was broken into two parts. This second part, continues from the May issue. It includes surface temperature effect on speed, and his answers to specific questions. ED.
Test results on surface color and heat absorption are reflected in the following graph. The color of a derby car's surface determines how much solar heat it will absorb, and in return, radiate to the wheels, increasing your racers speed. A white surface will absorb very little solar energy, about ten percent. However, a black surface can absorb almost 95 percent.
COLOR CURVE CHART
Using Stefan-Boltzmann's law, heat radiation is proportional to the 4th power of the absolute temperature of the radiating source. This can be carried one step further by stating that the quantity of heat from a pinpoint source depends upon the difference between the 4th powers of the absolute temperatures of the heat source (racer) and the exposed body (wheels). it will also vary inversely as the square of the distance separating them.
Radiated heat is radiated in straight lines. It is also radiated in all directions from any point. The larger the radiating source the more heat will be transferred. A black body will radiate the maximum possible energy at all wavelengths.
In actual tests, a black derby car and a soap box wheel (steel) were set in the sun for 20 minutes, and separated by 20 feet. The ambient air temperature was 77 degrees. The racer's surface temperature reached 172 degrees, and the wheel 156 . The wheel was then placed on the racer and it's temperature monitored. Theoretically the wheel should have reached a temperature of just a little over 167'. The temperature did rise to 162' in 20 minutes. However, in the first 5 minutes the temperature rose only 1.5 degrees.
This small temperature increase will help your speed by about 8 inches. A black car will get your wheels hotter and the hotter your wheels are, the faster-you are.
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