Ford Focus Forum banner
1 - 9 of 9 Posts

·
Registered
Joined
·
844 Posts
It's not based on actual speed but is on the rate of decelleration. For example, most manufacturers calibrate their systems to deploy at approximately 10-12 MPH into a FIXED barrier (i.e. a solid wall). But if you were to hit a parked car at 30 MPH, that car is going to move on impact and your actual rate of deceleration is greatly reduced. The same is true for hitting something like a pole if it bends/breaks. This is why some people will say that they hit something at a certain speed, but claim their airbags must be defective because they didn't go off.

Vehicle speed is NOT being directly monitored by the deployment sensor(s) - it's the RATE of decelleration that is.


And now for a trivia question: If you hit another car of equal mass head on and both are going 60 MPH at the time, are you subjected to the same force as if you hit a solid barrier at 120 MPH???
 

·
Registered
Joined
·
193 Posts
Discussion Starter · #4 ·
I am going to guess no. I would think into a barrier the force would be stronger because you are hitting a fixed object that will not budge, as opposed to two vehicles that will compress and have some give. Am I right? What do I win! What do I win!
 

·
Registered
Joined
·
4,983 Posts
And now for a trivia question: If you hit another car of equal mass head on and both are going 60 MPH at the time, are you subjected to the same force as if you hit a solid barrier at 120 MPH???
No, I believe that in theory, it would be equivalent to hitting a solid barrier at 60 mph.
 

·
Registered
Joined
·
556 Posts
I do know that it's more than hitting a barrier at 60 because that would just be your speed you need to multiply that because because both objects are moving, but I think there is more to factor in...ahh hell just to be different I'll say yah it's like hitting a [email protected] 120
 

·
Registered
Joined
·
438 Posts
I do know that it's more than hitting a barrier at 60 because that would just be your speed you need to multiply that because because both objects are moving, but I think there is more to factor in...ahh hell just to be different I'll say yah it's like hitting a [email protected] 120
I’m just going to post Isaac Newton’s Third Law of Motion.

“For every action, there is an equal and opposite re-action.”

So, hitting the wall at 120 mph, the wall is going hit you back at 120 mph, giving you totally different force. For example Lets say it takes 40 (N) to push on the wall, the wall will push on you with the same force 40 (n). You are going to experience force of 80 (N) not applying friction force. But If and only if you over come the friction force, you will eventually move the wall
 

·
Registered
Joined
·
844 Posts
Since each of the vehicles are going 60 mph, each one experiences a force similar to hitting a fixed wall at 60. Otherwise you'd have to be CREATING energy - which simply doesn't happen.

To better understand this (and put the "...equivalent of a 120 impact" legend to rest) visualize the impact from a side view in slow motion. If both vehicles are crushing (ABSORBING energy - not creating it) at approximately the same rate, you could almost draw a (theoretical) vertical straight line right where they're impacting. Since both vehicles are crushing at approximately the same rate, this straight line doesn't move...which makes this straight line represent a fixed barrier which is being struck at 60 mph from both sides.

Kind of confusing...but it's really kind of simple of you think about it from the perspective of both vehicles and not just one.

As for the winner's prize someone was asking about - it's the satisfaction of knowing you understand the real world and don't simply accept ongoing myths as fact. Great job!!
 
1 - 9 of 9 Posts
Top