வெள்ளத்தில் மாட்டிய Car-இல் இருந்து தப்பிப்பது எப்படி
4 Minutes
Escaping a submerged car in floods: students learn why car windows break differently and how tempered glass works. A Tamil science lesson.
- Laminated windshield glass versus tempered window glass
- How heating and rapid cooling make tempered glass strong
- Breaking a car window using headrest metal rods to escape
What this lesson teaches
To escape a car trapped in floodwater, passengers must break a side window rather than the front windshield. Side windows are made of tempered glass that crumbles completely when punctured, whereas the front windshield is made of laminated glass that stays glued together even when smashed.
Windshield versus side window glass
- The front windshield is made of laminated glass, which sandwiches a flexible vinyl sheet between two layers of normal glass.
- When an accident cracks the windshield, the broken glass fragments remain glued to the plastic sheet so sharp shards do not fly out and injure passengers.
- Side windows are built from tempered glass, a specialized glass engineered to be much tougher than ordinary glass.
- Because laminated glass holds firmly together even after extensive cracking, kicking or pushing through the front windshield is nearly impossible during an emergency.
How tempered glass gets its strength
Glass is originally made by heating silica from sand to 1500 degrees Celsius and cooling the resulting molten liquid into solid sheets. To convert normal glass into tempered glass for car windows, manufacturers reheat it to 600 degrees Celsius and then cool it down rapidly. Heating causes the glass atoms to expand away from each other, while cooling causes them to contract. Rapid cooling causes the outer skin to contract and harden almost instantly, while the inner atoms continue pulling inward as they cool, locking the core in strong tension and the outer surface in powerful compression.
How to break out and escape
- Hitting the side window with bare hands will not break it because the compressed outer surface easily resists blunt blows.
- Breaking the glass requires a hard, pointed object that can pierce the outer skin and disrupt the locked tension inside.
- If no emergency hammer is available inside the vehicle, passengers can pull the headrest completely off the car seat.
- The exposed metal rods at the bottom of the headrest have sharp edges that can be used to strike the corner of the side window.
- Once the internal tension is broken, the entire window crumbles instantly into tiny, dull pieces like powder, allowing a quick escape.