- Ab extends by 2mm and bc contracts by 2mm .
- Soldiers of bad character were branded bc .
- Glass-making flourished as early as 1350 bc .
- The tube abc shown is cantilevered with ab and bc in a horizontal plan .
the vertical displacement =1mm is normal to the bars ab and bc and hence does not affect their length. 豎向位移1mm垂直于AB和BC，故不影響它們的長度。