Just as a historical note, the World War 2 German Stuka dive-bomber used 20mm rounds to take out Soviet tanks.

That's a shitload of kinetic energy.

I also figured it would be lower because, well, physics. I think the spinning block was ever-so-slightly lower, but they were so close, practically millimeters it seems, that I am still curious about the lack of a greater difference.

The only thing I could think of that would cause this is that the initial rate of angular rotation on the spinning mass made up for the lower amount of direct kinetic energy from the bullet.
The bullet still conveyed the maximum amount of potential kinetic energy, but instead of transferring it solely to the objects linear acceleration, it transferred half to the objects linear acceleration, and the rest to the objects rotational acceleration, and by some principle of centrifugal or centripetal force that rotational energy somehow caused the block to reach the same height.

A shot in the dark, but that's my guess.

Essentially my guess is that the bullet can only transfer so much kinetic energy to accelerate the block upwards. Above that threshold it finds other ways of disposing of this energy. Why this threshold/diminishing return might exist idk.

So yeah, I think there must be some change in the efficiency of the transfer of energy in the two examples. Does smacking the bullet right in the centre create more sound? Does the bullet deform/heat up more in the first example because the block simple can't get out of the way fast enough? You'd think that spinning a block would take comparitively little energy compared to all those other inefficiencies. Perhaps if you were to increase the velocity of the bullet you might not see that large of a difference in the height it rises - rather the block would sustain more damage, the slug would pancake more etc etc.

It does seem raher counter-intuitive though. I'd like to know the explanation.

I thought you might be overestimating the force of a thrown baseball as compared to the steel ball bearing, so I tried to do some research and run numbers to compare.

Some googling says a baseball should weigh 5-5.25 ounces (about 1/3 of a pound).

Another page and some quick calculations that I might have screwed up[ (4*pi*.5*.5*.5)/3*.283 ] say that the ball bearing might weigh about .15 pounds -- a bit under half of the baseball.

On the other hand, the fastest pitch ever recorded in MLB (by Nolan Ryan) was 108.1 MPH or 158.5 feet per second. Harder to find data on "muzzle" velocity of a slingshot, but this page suggests that some people claim some slingshot projectiles can travel at 300 feet per second, but he argues that 180 to 200 fps is probably a more realistic high end for a .50 caliber lead ball (which would probably/possibly? be heavier than the 1" steel ball since lead is more dense). Anyway, there is at the very least a slight advantage to the slingshot here as compared to the fastest pitch ever recorded in MLB. Considering the draw length and pull strength of the slingshot in the video, I'd say it is probably actually much faster than the conservative 180-200 fps number from that page.

So then you've got @cosmovitelli 's formula (mass times velocity squared). The mass of the baseball is probably double that of the steel ball, but the velocity is probably 25-90% faster (or even more) and then squared. That probably overcomes the disadvantage in mass and then some.

Then again, this is all fairly academic as you suggested because the lethality of the bullets/projectiles is dependent on them being small enough to puncture, tear flesh, break/shatter bones, etc. Apply that kinetic energy to a very small impact site. However, in spite of its large size, I bet that steel ball could do a lot of damage given its kinetic energy -- which is what I would take away from their claims of it "hitting harder". I wouldn't want to stand in front of a Nolan Ryan fastball either, but given the choice between that and the slung steel ball... I'd take the plunk and have somebody take my base for me.

kinetic energy = mass x velocity squared

Bullets kill by punching holes in vital organs, fracturing bones into the blood and slicing veins and arteries - not by impact shock.
More like poking a thin metal rod into someones body than hitting them with a heavy object.

Only in hollywood do they throw people off their feet.

Sometimes they get it right:

http://youtu.be/f8j4GIRYbZw

What people with a jones for physics, kinetic energy, and the wonder of a child do with a decommissioned crane bucket....for the fucking win!

Upvote for a recent personal respect for Mr. Trampoline.....I only wish my own epic trampoline fail was captured on tape, it would have surely garnered over 100 votes for anyone who uploaded it....the physics involved alone would have been enough fodder for a paper on the wonders of kinetic energy vs. threshold displacement energy

My understanding is that a correct autorotation is NOT accompanied by a hard landing. However, it IS very difficult to pull off (hard---what a pun!), the closest personally analogy I can think of, being docking a boat by chopping the throttle while still tens of yards away from the dock, casting it up alongside just So---with all the kinetic energy elegantly spent before kissing the dock side.

The helicopter analogy, again, to my knowledge, is that once engine failure is clearly happening, you flatten the pitch, give up the lift the blades were generating, start falling and preserve main rotor RPM as much as possible---and you get exactly one chance and one chance only to pull pitch (make the rotor blades bite the air) at just the right distance above the ground to decelerate the helicopter just as all the rotational energy of the blades finishes spending itself in generating that last, final iota of lift--and then you kiss the ground.
Or not.

The wikipedia article on magnets is a good place to start. Magnets can lose their magnetism, but that's not the same as saying they have energy in them that's being used up like a battery.

If you stand next to a large lump of clay and then step onto the clay you've gained some potential energy. The taller the lump of clay the more potential energy you've gained. However, this energy hasn't come from the clay, you've had to use energy to gain it. It took you more energy to step onto the clay than you gained in potential energy so this couldn't be the basis for a perpetual motor.

Next to the lump of clay is a large bellows attached to a balloon. You step off the clay onto the bellows. You drop down to ground level and pump up the balloon a bit. You can repeat this process over and over until the balloon is pumped up. However, each time you step onto the clay it sags a bit and you're not so high up. After a while if you do this for long enough the clay will be well trodden down and each time you step off the clay onto the bellows it will have hardly any effect. The clay has lost it's ability to help you pump up the balloon. It's lost it's height. But at no point did it give you any energy to pump up the balloon. You used your own energy to step up onto the clay to give yourself the potential energy, which you then converted to kinetic energy by stepping onto the bellows and pumping up the balloon.

This is exactly the same as a magnet losing it's magnetism. It's not like a battery losing power by powering something else. There's no energy in a magnet. It never gives energy to anything else. Like a drive shaft doesn't power a car, it just helps move the energy from the engine to the wheels.

Magnets fool everyone by working at a distance. Everything else we deal with in a physical way has to touch something else to affect it. You can't get a nail into wood without physically hitting it with a hammer. Magnets confuse us and that makes it easy for scammers with their perpetual motion devices to make us believe things that aren't true. We don't have the right wiring to easily figure out what's going on intuitively.

Magnets simply don't work how you think they do, or how the maker of this video wants you to believe they do.

One day he's going to do this to the wrong kind of squirrel, and while he's standing there cackling and congratulating himself on another of man's triumphs over nature, the squirrel is going to unfurl her little arm flaps, perform a graceful 180 degree bank and enter a steep high-speed dive, razor-sharp incisors leading, and screaming death from above as she homes in on her new found nutty prey.

Kinetic energy is their ally. Never forget.

yes i'm not saying the roads are consistent, only more consistent than the shoulders.
Roads are generally no less than the width of 2 cars. Some consistency cuts manufacturing costs which will eventually be a factor in EOREI (energy returned on energy invested). Can it work....uhhh dunno. Many roads are created sectionally as it is. which is good. but yeah i have to worry about chains, rocks, studded tires....
Legally you wouldn't have any "takings" issues.

But IMHO, most technical solutions are further away than the more immediate solution - education, family planning, and worldwide contraception programs. the real problem is that there are too many people on the planet. We are consuming more of the ecosystem than we replenish. we need to USE less, but that necessarily means less people...which = more resources available per person, and less emissions.
Meanwhile keep working on the tech side to create efficiency.
Conceptually however, it is interesting to look at roads in energetic terms. They do produce all sorts of heat (and friction) and kinetic energy.

I had more or less this idea like this 15 to 20 years ago, though I didn't add the solar panel aspect until about 10 years ago, and kinetic energy soon after the solar aspect. I wanted to make roads out of a strong plastic with lights for the edge lines. There would be quick swap panels to make it quick and easy to fix broken sections.

The issues I figured would be making them strong enough and cheap enough. Never carried the idea past my head. My main goal initially was to make edge lines easier to see at night in the rain, the idea went from lite up edges to why not make the whole road out of a plastic, and add groves to help water fall to sides better than conventional roadways. Then I eventually thought, why not make all that surface useful and make them capture solar as well, and eventually decided that since each panel is suspended on the base anyhow, why not capture the kinetic energy of the traffic pushing down on it and springing back up (was never sure if the limited motion that you could safely allow on a freeway would be enough to harness or not). I figured it would be too expensive and eventually decided the better solution would be to bury roads and make them all tunnels then turn the overhead areas (where the freeways are now) into green ways with solar roof collection areas as well, or just put roofs over the freeways and skip the green way effect... regular roads would still be the panel type... nice to see I was onto an idea anyhow.

>> ^chingalera:

>> ^SevenFingers:
If that truck was going a bit slower the driver probably wouldn't have walked away!

Can't really say who's gonna live or die when that much kinetic energy manifests..That guy is one lucky, non-water-truck-driving-job-havin' MOFO!!


http://en.wikipedia.org/wiki/Vacuum_truck

http://www.badgerinc.com/

>> ^SevenFingers:

If that truck was going a bit slower the driver probably wouldn't have walked away!


Can't really say who's gonna live or die when that much kinetic energy manifests..That guy is one lucky, non-water-truck-driving-job-havin' MOFO!!

>> ^Barbar:

Applying the oversimplified version of laws that you learned in early physics classes to reality can often leave you in stunned silence when reality seems to defy them. Things like the dimples on golf balls or sailing ships moving upwind are classic examples of things that you wouldn't expect to even be conceivable unless you saw it in action.


Conceivable or not, none of the things you mentioned break the first law of thermodynamics.

One situation where the system could work would be if the car was driving into a strong headwind. This would give an energy input into the system. It could be perhaps developed to extend the blades if there is a strong enough headwind, and retract them if there isn't, but if there is no breeze, there will be a net loss from using the blades.

If the car is driving through stationary air then the air it's passing through will have no kinetic energy. After passing over the blades the air will be moving, it will have gained kinetic energy. That energy will have been taken from the car. It's as simple as that. No complicated equations needed. You'd need the complicated equations if you wanted to calculate exactly how much energy is lost, but you don't need them to see that energy would be lost.

If wind is factored into it then the air already has kinetic energy, which would be extracted by the fan, but the wind would be and external source of energy (in the same way that a wind turbine isn't in any way a perpetual motion device, it's obvious where the energy is coming from).