[题目]下列关于“验证机械能守恒定律实验的实验误差的说法.正确的是( )A．重物质量的称量不准会造成较大误差B．重物质量选用得大些.有利于减小误差C．重物质量选用得较小些.有利于减小误差D．打点计时器选用电磁打点计时器比电火花计时器误差要小题目和参考答案——青夏教育精英家教网—

题目内容

【题目】下列关于“验证机械能守恒定律”实验的实验误差的说法，正确的是（）

A．重物质量的称量不准会造成较大误差

B．重物质量选用得大些，有利于减小误差

C．重物质量选用得较小些，有利于减小误差

D．打点计时器选用电磁打点计时器比电火花计时器误差要小

【答案】B

【解析】为减小实验误差，重物应选质量大些的，且重物质量不需称量，A、C错，B正确；电磁打点计时器的振针与纸带间有摩擦，电火花计时器对纸带的阻力较小，故选用电磁打点计时器误差大些，D错误．

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The production of coffee beans is a huge, profitable business, but, unfortunately, full-sun production is taking over the industry and bringing about a lot of damage. The change in how coffee is grown from shade-grown production to full-sun production endangers the very existence of, certain animals and birds, and even disturbs the world’s ecological balance.

On a local level, the damage of the forest required by full-sun fields affects the area’s birds and animals. The shade of the forest trees provides a home for birds and other special(物种) that depend on the trees’ flowers and fruits. Full-sun coffee growers destroy this forest home. As a result, many special are quickly dying out.

On a more global level, the destruction of the rainforest for full-sun coffee fields also threatens(威胁)human life. Medical research often makes use of the forests' plant and animal life, and the destruction of such species could prevent researchers from finding cures for certain diseases. In addition, new coffee-growing techniques are poisoning the water locally, and eventually the world's groundwater.

Both locally and globally, the continued spread of full-sun coffee plantations (种植园)could mean the destruction of the rainforest ecology. The loss of shade trees is already causing a slight change in the world's climate, and studies show that loss of oxygen-giving trees also leads to air pollution and global warming. Moreover, the new growing techniques are contributing to acidic(酸性的) soil conditions.

It is obvious that the way much coffee is grown affects many aspects many aspects of life, from the local environment to the global ecology. But consumers do have a choice. They can purchase shade-grown coffee whenever possible, although at a higher cost. The future health of the planet and mankind is surely worth more than an inexpensive cup of coffee.