问题 问答题 简答题

简述浮沉试验的过程?

答案

参考答案:

浮沉试验是根据阿基米德原理进行的,把选定的煤样放进具有一定密度的重液中,密度小于重液的煤就会浮起,大于重液密度的煤就会下沉,密度刚好等于重液密度的煤则处于悬浮状态。试验过程中,把浮起的和一部分悬浮的煤取出,称为浮物,把沉下的和另一部分悬浮的煤取出,叫做沉物。

若把重液配制成自低到高n个不同密度的重液,使煤依次在n个不同密度重液中进行浮沉,就可得到(n+1)个密度级的煤。浮沉试验煤样一般要先经筛分试验分成窄粒度级,各粒度级分别进行浮沉试验,最后将各粒度级的浮沉数据进行综合计算。如果煤样粒度级别过宽,会影响浮沉试验的精确性。

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    People in the United States honor their parents with 2 special days: Mother's Day on the

second Sunday in May and Father's Day on the 3rd Sunday in June. These days are to show

love and respect for parents. They raise their children and educate them to be responsible citizens.

They give love and care. These two days offer an opportunity to think about the changing roles

of mothers and fathers. More mothers now work outside the home and more fathers must help

with childcare.

     These two special days are celebrated in many different ways. On mother's Day, people

wear carnations. A red one symbolizes a living mother. A white one shows that the mother is

dead. Many people attend religious services to honor parents. It's also a day when people whose

parents are dead visit the cemetery(grave). On these days families get together at home as well

as in restaurants. They often have outdoor barbecue for Father's Day. These are days of fun and

good feelings and memories.

     Another tradition is to give cards and gifts. Children make them in school. Many people make

their own presents. These are more valued than those bought in stores. It's not the value of the

gift that is important, but "the thought that counts". Greeting card stores, florists, candy makers,

bakers, phone companies and other stores do lots of business during these holidays.

1.Which is NOT a reason for children to show love and respect for parents?_____

A. Parents bring up children.

B. Parents give love and care to children.

C. Parents educate children to be good persons.

D. Parents pass away before children grow up.

2.What do you know from the passage?_____

A. Both festivals are in May.

B. Fewer women worked outside the home in the past.

C. Not all the children respect their parents.

D. Fathers are not as important as mothers at home.

3.Which do you know about "carnation"?______

A. It only has two kinds of color.

B. It refers to the special clothes people wear on Mother's Day.

C. It's a kind of flower showing love and best wishes.

D. People can wear them only on the second Sunday in May.

4.On Mother's Day and Father's Day _____.

A. people sometimes have family parties B. everyone goes to the cemetery

C. children always go to parents' home D. hand-made cards are the most valuable gifts.

5.What do you think "florists" do ?______

A. They sell flowers.

B. They make bread or pastry.

C. They offer enough room for having family parties.

D. They sell special clothes for Mother's Day and Father's Day.