When a tensile stress is applied the semi-crystalline polymer first deforms elastically. Hence, whether the system behaves plastically or elastically is independent of the applied normal force. Microstructured polydimethylsiloxane thin films can elastically deform when pressure is applied. Springs do not require as much wear resistance, but must deform elastically without breaking. Neutrons can elastically scatter off nuclei, causing the struck nucleus to recoil. For formula 136, the surface behaves elastically during contact. If it elastically collides with the surface, then it would return to the bulk gas. The case, which had been elastically expanded by chamber pressure, contracts slightly. At low temperatures, molecules are more likely to stick together instead of rebounding elastically. Much engineering design is based on the assumption that materials behave elastically. Some horsecarts found in Celtic graves show hints that their platforms were suspended elastically.