The centerpiece of curling(冰壶)is the curling stone. Kays of Scotland has been making curling stones since 1851, when William Kay and his sons Andrew and Thomas set up a workshop in Mauchline, Ayrshire, in southwest Scotland. Kays is still owned by the relatives of the founder, and today it is the only curling stone maker left in Scotland.
   Used in a highly competitive sport, the curling stones are made to exact standards. First, stones are sliced and then into round “cheeses”. Finally, the cheeses are shaped and polished into curling stones in a series of steps.
   Each stone must weigh 44 pounds. Each must have a maximum diameter (直径) of 36 inches. Polishing is done by hand on a wheel using water, diamond-talcum power, and felt. Finishing the stone’s “running edge” is done entirely by hand with a special kind of paper and a digital measure and magnifying glass (放大镜). Lastly, a handle(把手) is fitted into holes on the top of the stone. Stones are computer-matched into pairs. Sixteen stones----8 pairs----are needed for a game, and since curling game field usually have 6 lanes, each game field needs 96 matched stones!
   Kays is a small company, employing less than ten skilled workers. Master craftsman and co-owner James Wyllie is skilled at all phases of curling stone making and is also an enthusiastic curler, as well as active member of Mauchline’s Burns Club, which meets regularly to honor well-known Mauchline residents.

如图所示是测量小车沿斜面下滑的平均速度的实验．

（1）该实验目的是练习用 ____ 和 ____测平均速度．

（2）该实验原理是　 ____　

（3）实验时观察到，小车沿斜面顶端下滑到斜面底端的运动是 ____直线运动．（选填“匀速”或“变速”）

（4）实验中测得路程s₁上的平均速度为v₁，路程s₂上的平均速度为v₂，路程s₃上的平均速度为v₃．那么，v₁、v₂、v₃的大小关系是　 ____　．（选填＞、＜、=）

用“分子”、“原子”、“离子”、“元素”填写：

①一切物质都是由____组成；

②在汞中，化学变化的最小粒子是汞____；

③氢气是一种可持续的理想的绿色能源，保持氢气化学性质的最小粒子是氢____；

④硫酸铜（CuSO₄）是由Cu²⁺和SO₄^2-两种____构成。