Non-Destructive Way To Demonstrate Effects Of Acceleration?

Funny! But I'm pretty much convinced that just as in "Oh brother, Where Art Thou" where George Clooney and his buddies are having a picnic under the big oak tree, I believe I would hear the words, "I just don't get it!"

Unfortunately, I can't wack them with a branch and lecture them about it being all about the money!

It depends on what material is being accelerated, or decelerated. Some materials and machines (rockets, F-18's launched from aircraft carriers) can withstand an impulse acceleration, some can't (jackhammers, yes - the concrete, no). Human bodies aren't very good at absorbing impulse accelerations. Ask Dale Earnhardt.

Uhhhh...I think asking Dale is going to be a bit difficult, is it not?

It depends on the application.

What do you mean when you said "gradual acceleration" and "instant acceleration". Is it the change of acceleration you are talking here? In simpler words, JERK.

It's okay, I suck too with mechanics, but the thing you are referring here is impact loading and fatigue stress.

You can never cut a rebar by bending with slow motion, you need some rapid bending stroke to be successful.

F = M*A

Drop an egg on the floor.

Make them be crash test dummies.

A belly-flop off a 3-meter board would be less destructive.

Just explain that no one likes a Jerk.

https://en.wikipedia.org/wiki/Jerk_(physics)

Yes, the Jerk factor is very significant in what is currently being done. I want to show that changing the Jerk to zero makes a big difference.

As Solar Eagle pointed out F = M * A but I think the formula for motion is a little closer to what I am trying to describe. The problem is that there are at least two factors where the modulus of elasticity is also a factor. In fact, it is a little bit like trying to write the formula for a golf swing, only worse.

At least with a golf ball the modulus of elasticity is always the same because you use the same ball over and over. The problem I'm dealing with is like using random balls (from anything between cotton, bean bags and brick) while trying to hit the same moving target with the same swing. It just does not perform the same for every object.

With Jerk approximately equal to 0 and Acceleration more or less constant I should be able to ignore the modulus of elasticity. This is a problem where the physics interferes with the capacity of the material handling process and limits what can go through the system. All because the Jerk is a huge impulse.

Nice one Rix.

In your example you neglected an aspect although the sketch has it: the rheological material behavior.

As you sketch shows it the material has in parallel to the spring a "damper". This "damper" has a resistance proportional to the deformation velocity. This is the reason why a material which you can deform quite easy at ow speed will break at high speed and asking also for a higher force.

In general the Young modulus is obtained by tests at low speed, if samples are tested at high speed the result is different : it is higher! For metals which have a low "damper" the effect is not very important but for other materials it is.

• Take the plastic holder from a 6-pack of cans.

• Fold it over until you have 1 hole.
• With the middle finger of each hand pull it apart as quickly as you can - it should break.
• Now, with another folded holder, try to break it, but this time pulling slowly - it will be nearly impossible to break!
• Drink the beer

I'm ready for the beer right now. No need to remove the plastic holder!

See my previous reply regarding a better description of the problem. I'll save you a can or two.

What's the last thing to go through a flies brain when it hits your windscreen?

Its ar****le.

A dramatic demonstration of autobrake-on-collision feature on Mercedes....

Sorry, I think you need to define your terms. "Better" depends on context, point of view, and scale, and what your goal is. If you are trying to shoot a deer with a rifle, from your point of view an "instant" acceleration of the bullet might cause a recoil so strong that it drives the rifle butt through your shoulder and through the wall behind you. You want an acceleration appropriate to the mechanical system. From the point of view of the deer, gradual acceleration is much, much better, so that the bullet drops out the end of the barrel onto the ground at your feet.

You don't mention any context, scale, or goal in your post.

Compare a powerful sling shot to a rifle. Both will propel a ball or shot but the sling shot accelerates slowly compared to the bullet. Or an arrow shot from a bow will be another example.

I'm surprised it's necessary as well; you might get away without a gradual start - just don't break something or shoot it across the room. If you limit the energy for an accelerating impulse you may not need to provide gradual acceleration at all. What is the requirement? Why make it more complex than it needs to be?

Crash test dummies volunteer for the job because they enjoy the thrill of the crash.

Simple demonstration:

You have a baseball bat.

Give the mechanical engineer a nudge with it.

Then hit him with it.

You will most likely have a convert at your feet.

I have been considering this demonstration, I just didn't think I would start with that.

Hold onto a loose/unmounted 1Ph AC motor then switch it on. Next try holding onto a similar sized rotor 12v DC starter motor when switched on. Similar sized rotors as in similar mass. Jim