In a science lab, a teacher instructed students to attach a piece of very fine steel wool to a clamp stand inside a fume hood. The students then lit a burner placed under the steel wool. The metal strands began to glow bright red and flames filled the steel wool. After the burner was turned off, the metal continued to burn, leaving behind reddish-brown strands that collapsed into a powder when it was touched after cooling. Based on these observations, did the steel wool undergo a chemical change or a physical change? Explain your answer.

Which statement best describes how private industry decides where to spend the money on research and development

An internally reversible refrigerator has a modified coefficient of performance accounting for realistic heat transfer processes of where qin is the refrigerator cooling rate, qout is the heat rejection rate, and is the power input. show that copm can be expressed in terms of the reservoir temperatures tc and th, the cold and hot thermal resistances rt,c and rt,h, and qin, as where rtot rt,c rt,h. also, show that the power input may be expressed as 1.39 a household refrigerator operates with cold- and hot-temperature reservoirs of tc 5 c and th 25 c, respectively. when new, the cold and hot side resistances are rc,n 0.05 k/w and rh,n 0.04 k/w, respectively. over time, dust accumulates on the refrigerator’s condenser coil, which is located behind the refrigerator, increasing the hot side resistance to rh,d 0.1 k/w. it is desired to have a refrigerator cooling rate of qin 750 w. using the results of problem 1.38, determine the modified coefficient of performance and the required power input w under (a) clean and (b) dusty coil conditions. internally reversible refrigerator qout qin w high-temperature reservoir low-temperature reservoir th th,i tc,i tc high-temperature side resistance low-temperature side resistance w qin th tc qinrtot tc qinrtot copm tc qinrtot th tc

What is the name of the perceived change in a sound wave’s frequency due to motion between the observer and the sound source?