Problem: Film speed is found from a plot of optical density vs. log of exposure for the film, known as the Dlog H curve or HurterDriffield curve. There typically are five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. For black-and-white negative film, the "speed point" m is the point on the curve where density exceeds the base + fog density by 0.1 when the negative is developed so that a point n where the log of exposure is 1.3 units greater than the exposure at point m has a density 0.8 greater than the density at point m. The exposure Hm, in lux-s, is that for point m when the specified contrast condition is satisfied. The ISO arithmetic speed is determined from:
What is film speed combined with to produce optical density?
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Answer: unanswerable

Problem: Paper made from mechanical pulp contains significant amounts of lignin, a major component in wood. In the presence of light and oxygen, lignin reacts to give yellow materials, which is why newsprint and other mechanical paper yellows with age. Paper made from bleached kraft or sulfite pulps does not contain significant amounts of lignin and is therefore better suited for books, documents and other applications where whiteness of the paper is essential.
What particle is associated with the yellowing of newspapers?
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Answer: lignin

Problem: On the uneven bars, the gymnast performs a routine on two horizontal bars set at different heights. These bars are made of fiberglass covered in wood laminate, to prevent them from breaking. In the past, bars were made of wood, but the bars were prone to breaking, providing an incentive to switch to newer technologies. The width and height of the bars may be adjusted. In the past, the uneven parallel bars were closer together. They've been moved increasingly further apart, allowing gymnasts to perform swinging, circling, transitional, and release moves, that may pass over, under, and between the two bars. At the Elite level, movements must pass through the handstand. Gymnasts often mount the Uneven Bars using a springboard, or a small mat. Chalk and grips (a leather strip with holes for fingers to protect hands and improve performance) may be used while doing this event. The chalk helps take the moisture out of gymnast's hands to decrease friction and prevent rips (tears to the skin of the hands), dowel grips help gymnasts grip the bar.
How have the bars changed over the years?
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Answer:
They've been moved increasingly further apart