Why do people die when they hit a tree if all modern cars have air bags?
In: Engineering
Trees are very sturdy and don’t absorb much impact. Things like telephone and light poles are specifically designed to break and not suddenly stop the car. When calculating force the timeframe is extremely important. Going 60mph to 0 over 2 seconds is survivable. Going 60 to 0 over 0.5 seconds is very much less. Airbags and seatbelts are designed not to stop you but to slow the deceleration as much as possible. Same with the crumple zones on the vehicle. There is only so much that can be done from the vehicle side so when you impact something that doesn’t budge at all the expected force skyrockets. Your odds of survival drop accordingly.
Trees don’t have crumple zones, if they don’t break they stop a car *very* quickly. There’s only so much an airbag can do…if you stop the car fast enough the airbag can’t stop you before you run into the dashboard or seatbelt or both.
When a car hits another car they each have several feet of compression to absorb energy. Even if you hit a wall you at least have the full width of bumper and crush zones to absorb and dissipate energy. A tree has basically no flex and is thin enough that most of the built-in crumple zones of the car can’t get into play. The car can’t dump enough energy fast enough to keep you safe.
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