Accelerate Safely - net force and time for collisions

We take our first form of Newton's Second Law of Motion and modify it.

It's still the 2nd Law but a different look. Newton found that momentum is an important quantity so we express it in terms of "Net Impulse" and "Change in Momentum."

When you're driving your car and you need to stop, there are a few options.  Brakes are the obvious choice but you could also run into a house-sized boulder.  Maybe even use the runaway truck ramp.

The right side of that equation is the same for each of the choices above so only the product is a constant but the proportions on the left can change.

We can extend the time for a smaller NET force or reduce the time which requires a larger NET force.  Here are some examples.

  vs.   

Which is the more effective helmet?

we don't want intrusion.

We want longer time of impact.

 vs. 

Which court protects the body more?

The suspended wood floor gives.

More time and less net force applied.

This looks horribly uncomfortable but the suspended floor for a gymnastics competition allows a lot of impact time for smaller net forces applied.

Divers 'land' in water.  Longer acceleration time for smaller net force applied.

Remember the egg toss?  How do you catch the egg without breaking it?

Boxing gloves protect your hands.  Shoes protect your feet on impact.  chubby arms protect your bones.  Finger pads protect your fingers.  And auto safety depends on the reduced net force required for a shorter impact time.

Crumple zones:

Air Bags:

My friend was almost killed for lack of a side air bag.  His wife was driving and pulled out across traffic in front of a speeding SUV.

He was on the side opposite the impact and his head impacted one of the pillars or the window on the right.  One helicopter flight later he had a portion of his skull removed to deal with the swelling on the brain.  Modern side impact air bags would stay inflated long enough to avoid this problem.

Notice that everything in your car is covered with plastic and is relatively soft for the same reason.

There has been a 25% decrease in auto fatalities in the past decade resulting, in large part, from improved safety features such as side impact air bags and electronic stability control.  We're happy to have it.

Just remember that in all these situations and many more we stop something over a longer time to avoid the large net force that would otherwise cause the acceleration.

I choose the bottom option unless I want to break the egg.