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某同学想知道斜面长和省力的关系，做了以下实验：他取了几个高度相同，但斜面长不相同的较光滑的斜面，用一个弹簧测力计将一个重为12N的方块物体匀速拉向斜面，记录拉力与斜面长关系如下表：

（1）从表中前4组数据可知：在高度一定时，______．

（2）根据表前4组数据，作出在高度一定时，拉力F与斜面长L的关系图：

（3）表中第5组数据没有遵循前面的规律，分析原因可能是：______．

（4）如果排除上述因素对实验的影响，则斜面长为1.4m时，拉力F的大小应为______N．

答案

（1）由数据可知，斜面长度在不断增大，拉力在不断减小．

故答案为：斜面越长越省力；

（2）描点连线．

故答案为：

；

（3）随着斜面的增长，物体对斜面的压力越来越大，所以可能是此斜面的摩擦太大．

故答案为：此斜面摩擦太大；

（4）由前面4组数据可知，拉力与斜面长度数值的乘积是不变的，都为6，所以当长度为1.4m时，拉力为6÷1.4≈4.3（N）．

故答案为：4.3．

填空题

Seasick Try Controlling Your Breathing


If you get seasick easily, you may prepare for boat rides with pressure-point bracelets, ginger, or a prescription skin patch. (1) The technique presumably works because it helps control gravity sensors in the abdomen-a lesser-known input to our fine-tuned balance system.
(2) The inner ears sense motions of the head; the eyes see where the head is; and tiny sensory organs in muscles and tendons sense where the rest of the body is. More recently, researchers have realized that sensors in many other parts of the body also play a role: in the abdomen, the lower organs, and even blood vessels. (3) But if one or two don’t match up, the brain gets confused and we become nauseated.
Scientists knew the most sickening motions closely match the rate of natural breathing; they also knew that people naturally tend to breathe in time with a motion. (4)
Researchers from Imperial College London enlisted 26 volunteers to sit in a tilting, rocking flight simulator and coordinate their breathing in various ways with the motion. (5) The natural tendency was for volunteers to inhale on every backward tilt, in rhythm with the rocking. (6) They felt even better if they breathed slightly faster or slower than the cyclic heaving of the chair; using that technique, the time until onset of nausea was 50% longer than during normal breathing.
(7) Abdominal sensors are known to send motion signals to the brain more slowly than those in the inner ear because they’re farther away from the brain and because abdominal organs have more mass, which means they resist movement a tiny bit longer. (8) But if the diaphragm opposes gravity-induced stomach motions with controlled breaths, there is less sensory conflict and less nausea. "This technique is very good for mild everyday challenges," says medical research scientist Michael Gresty, a member of the study team. "it’s completely safe, and it’s not a drug."
A. But if the subjects exhaled on every backward tilt, they didn’t get sick as quickly.
B. As long as all of these sensors send matching signals to the brain, we feel oriented.
C. Now there’s one more remedy: timing your breathing to counteract the nauseating motion.
D. So why do these tactics work
E. The brain is traditionally thought to sense body position in three ways.
F. The time lag between the two types of sensors creates a mismatch that builds up in the brain and makes us gradually sicker, the researchers say.
G. The tests lasted up to 30 minutes, or until subjects felt moderately sick.
H. But no one had ever tested whether breathing out of time with a motion could prevent nausea.
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判断题

道路上的水在夜间发光、反光。
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