"It's not the speed that kills you...."

@bowman81 Exactly. But the stop kills you because of the force of impact, and this decal shows the formula for force = mass times acceleration (rate of change of velocity)

@bowman81 it is the speed at which you suddenly stop. If you suddenly stop at a speed of 1 mph it's not going to kill you. But if you stop at a speed of 100 mph it will kill you. So it is a combination of speed and suddenly stopping

@DrWatson you seem to be trying to say that speed is not a part of the equation. My point is that speed plays a role in the equation and is a part of what kills you. There is a big difference between 1 mph and 100 mph.

@James25 The equation is F = ma.

@DrWatson "Newton's second law of motion states that F = ma, or net force is equal to mass times acceleration. A larger net force acting on an object causes a larger acceleration, and objects with larger mass require more force to accelerate. Both the net force acting on an object and the object's mass determine how the object will accelerate."

So if you have a car that accelerates to one mph and hits a cement wall you won't die. But if you have a car that accelerates to 100 mph and you hit a cement wall you will die.

"Newton's Second Law: Force His second law defines a force to be equal to change in momentum (mass times velocity) per change in time."

So whether you describe it as acceleration momentum velocity or speed it is a part of the equation.