问题 实验题

在探究杠杆平衡条件的实验中:

(1)小明发现杠杆右端低左端高,要使它在水平位置平衡,应将杠杆右端的平衡螺母向_____调节.小明调节杠杆在水平位置平衡的主要目的是_____.

(2)如图甲所示,在杠杆左边A处挂四个相同钩码,要使杠杆在水平位置平衡,应在杠杆右边B处挂同样钩码_____个.

(3)如图乙所示,用弹簧测力计在C处竖直向上拉,当弹簧测力计逐渐向右倾斜时,使杠杆仍然在水平位置平衡,则弹簧测力计的示数将_____(变大/变小/不变),其原因是_____

(4)小明在实验中多次改变力和力臂的大小主要是为了_____.

答案

(1)左;便于直接从杠杆上读出力臂的大小  

(2)3  

(3)变大;拉力的力臂变小,在阻力及阻力臂不变的情况下,动力臂变小,则动力变大  

(4)多次实验总结得出实验的规律,避免实验的偶然性。

单项选择题

If soldiering was for the money, the Special Air Service (SAS) and the Special Boat Service (SBS) would have disintegrated in recent years. Such has been the explosion in private military companies (PMCs) that they employ an estimated 30 000 in Iraq alone -- and no government can match their fat salaries. A young SAS trooper earns about£ 2,000($3 500) a month; on the "circuit", as soldiers call the private world, he could get £15 000. Why would he not

For reasons both warm-hearted and cool-headed. First, for love of regiment and comrades, bonds that tend to be tightest in the most select units. Second, for the operational support, notably field medicine, and the security, including life assurance and pension, that come with the queen’s paltry shilling.

Although there has been no haemorrhaging of special force (SF) fighters to the private sector, there has been enough of a trickle to cause official unease. A memo recently circulated in the Ministry of Defence detailed the loss of 24 SF senior non-commissioned officers to private companies in the past year. All had completed 22 years of service, and so were eligible for a full pension, and near the end of their careers. Yet there is now a shortage of hard-bitten veterans to fill training and other jobs earmarked for them, under a system for retaining them known as "continuance."

America has responded to the problem by throwing cash at it, offering incentives of up to $150 000 to sign new contracts. The Ministry of Defence has found a cheaper ploy. It has spread the story of two British PMC employees, recently killed in Iraq, whose bodies were left rotting in the sun

The word "security" in the second paragraph most probably means()

A. protection

B. document

C. certificate

D. safety

名词解释