题干

黑板“反光”时为什么看不清黑板上的字?为了保护同学的眼睛,请根据所学的物理知识提出改变这种状况的建议.

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答:黑板使用时间长了表面会变得比较光滑,当外面强光照射到时会发生镜面反射,导致有些同学看不到上面的文字,会“晃”着一些同学的眼睛;

为了保护同学的眼睛,可以把黑板打磨的粗糙些,让光在黑板上发生漫反射;可以改换学生的位置或改变黑板的角度;可以用一些不易反光的材料做黑板.

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    Cycling or even walking in city areas can be a little dangerous, thanks to the fact that one is sharing the road with vehicles that are increasingly getting larger and heavier. A recent study proves that of the 1.27million people that die in road traffic crashes each year, about half are walkers, motorcyclists and cyclists. Now there may be a solution that could provide at least some help to protect this helpless group---an airbag!

    If you are worried that this safety measure will involve you taking around a heavy package or worse still, wrapping yourself inside an ugly plastic bag, the bag is fitted not on the human, but on the outside of the vehicle. And, while there are several versions of the idea in the works, the one most recently unveiled by Dutch car company TNO, seems to be the most advanced and ready to go into production.

    In the works since 2011, the airbag covers only the lower part of the windshield. This will provide the much needed buffer(缓冲)between the person's head and the pane of glass he/she would otherwise meet.

    The chain of events leading to an airbag cause are quite simple---A camera fitted beneath the rear-view mirror monitors the vehicle's closeness to a walker or cyclist. Any contact with either one of them sets off the sensors in the car's bumper and quickly blows up the airbag. In addition to that the sensors also set off the car's automatic brake, reducing the chances if an even worse injury.

    In tests conducted using a model, the success of not getting injured after being hit by a car travelling at about 40km/h was about 50-50! While not perfect, it will still result in reducing the number of deaths by a huge amount.

    With TNO ready to license its technology to car makers and many more companies trying to develop similar concepts, we would not be surprised if outer airbags become a standard feature in every car pretty soon.