Hot Rail, Cooler Ramp
On a sunny July day at Riverside Skate Park, Mateo Ruiz noticed that the steel grind rail felt much hotter than the wooden ramp beside it. His club coach checked with an infrared thermometer. At 9 a.m. the rail, the ramp and a full water bottle on the bench had all read about 22 °C. By 3 p.m., after hours in the same sunshine, the rail read 48 °C, the wooden ramp 36 °C and the water bottle 31 °C. Mateo wondered why objects in the same sunlight reach such different temperatures.
Back in science class, his group planned an investigation. Each sample had the same 10 cm by 10 cm top surface, painted the same flat black so that each one would absorb light in the same way. The samples were steel, concrete, wood and water held in a thin black tray. A thicker block or deeper tray has more mass. Every sample started at room temperature, 20 °C.
The teacher clamped a heat lamp 30 cm above each sample and switched it on and off. The group read a probe thermometer under the middle of each block, or in the stirred water, when the lamp went off. From the lamp's power and the size of the top surface, the teacher estimated that each sample took in about 160 J of energy for every minute under the lamp. The group repeated every trial on a second day, and each result came out within 1 °C of the first, so the table shows the first set of results.