请写出如图18所示的几个实验所揭示的物理道理：

甲：                                                                     

乙：                                                                     

丙：                                                                     

丁：                                                                     

请写出如图18所示的几个实验所揭示的物理道理：

甲：                                                                     
乙：                                                                     
丙：                                                                     
丁：                                                                     

请写出如图18所示的几个实验所揭示的物理道理：

甲：                                                                     

乙：                                                                      

丙：                                                                     

丁：