题干

小强为“探究滑动摩擦力大小(f)与哪些因素有关”,将家里的可调速跑步机传送带调成水平,找来两个相同的长方体木块(每个重G,上表面ABCD面积为2S0,较光滑;下表面A′B′C′D′较粗糙;侧面CDD′C′面积为S0,和“下表面”一样粗糙).用测力计拉着一个木块(其上可加放木块),维持木块在传送带上对地静止并读出拉力T。为确定f与压力F、接触面粗糙程度、相对运动速度、接触面积大小的关系,小强所做实验记录如下:

步骤

压力F

接触面及面积

粗糙程度

带速

测力计T


1

G

A ′B′C′D′

2S0

较粗糙

V0

4N

2

G

A′B′C′D′

2S0

较粗糙

2V0

4N

3

G

ABCD

2S0

较光滑

V0

2N

4

G

CDD′C′

S0

较粗糙

V0

4N

5

2G

ABCD

2S0

较光滑

V0

4N

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    The BBC was founded in 1922, including radio and television services. It is based at Broadcasting House in London.

    The BBC is controlled by some governors chosen by the government, but these people have freedom and the government can't interfere(干扰). That is, the BBC is supposed not to be the mouthpiece(代言人)of the government. It has to be as fair as possible in giving radio and television time to, for example, political parties and religious groups.

    There is a kind of interesting service in British­rental services. Many people prefer to rent their television sets instead of buying them.

    The rent for a black and white set is about 80 pence a week. The rent of a color set is more than twice that of a black and white set. If the sets go wrong, people can have them repaired free of charge or replaced immediately.

    Everyone has to buy a yearly license, since there is no advertising on BBC radio or television. It is from the sale of licenses that the BBC gets most of its money. A license for a black and white set costs 8 pounds, and for a color set 18 pounds a year.

    There are four special radio channels, which broadcast different kinds of programmes. Radio 1 is mainly pop music. Radio 2 deals with light music, sports and other programmes. Radio 3 broadcasts serious music, talks on serious subjects, etc. News broadcasts are mainly given by Radio 4.

    There are special programmes for Northern Ireland, Scotland, Wales, and certain parts of England. It also broadcasts programmes about Britain — in many different languages as well as in English to all parts of the world.