题干

如图所示的情景,是为了验证____原理.实验中,用量筒测出两次示数差(V2﹣V1),这是为了进一步算出____力的大小. 在“验证凸透镜成像规律”的实验中,实验前要记下凸透镜的____.在测量牛奶密度的实验中,要多次测量牛奶的质量和对应的体积,这样做是为了____

上一题 下一题 0.0难度 选择题 更新时间:2013-11-26 09:44:15

答案(点此获取答案解析)

阿基米德,排开液体所受的重,焦距,减少误差

同类题5

根据短文内容,选择最佳答案。

    Each summer,you hear news that some sports players are sent to hospitals because it is too hot. Our bodies can't be outside in the sun for a long time. So in hot summers,be careful about playing sports outside.

    Firstly,to play sports safely in hot weather,you must drink water. Sports drinks are great for athletes,but they have so much sugar that they'll dehydrate(使脱水)you more. However,drinking a few bottles of sports drinks will be good for you.

    Secondly,be sure to take enough breaks to let your body rest. If your coach doesn't let you take enough breaks in the heat,don't wait until you feel uncomfortable. Just be honest with your coach when you need breaks.

    Thirdly,when you have a break,don't sit in the sun. With the sun beating down on you,you'll only heat up and sweat(冒汗)more. Take a seat under a tree,or even better,go indoors for a little while. Cooling yourself down can help you stay active longer.

    Fourthly,remember that the earlier in the day you start your exercise,the cooler it will be. If you can start practice before the sun comes up,you have a few good hours to practise in the cool hours of the morning. Also,the earlier you practise,the earlier you can finish the exercise. If you need more practice time,come back to the field later in the evening,when the sun is setting.

    Last but not least,you should watch what you eat. Eat food which is high in water,starch(淀粉)and carbonhydrate(糖类),but be sure to get a good balance in your diet.

    As long as you pay attention to the above,playing sports safely in the heat isn't a difficult thing.