(3分）在图中，甲是用绳和木棍体验“滑轮组”威力的装置；乙是正在旋转着升降的滚摆；丙是用于“探究水和沙子吸热升温的属性”的装置．

(1）图甲证明了                                                                    ； 
(2）图乙说明了                                                                    ； 
(3）图丙的实验中用加热时间的长短表示物质                                            ．