I wonder if a grand-piano-sized rock dropped on top of an M1 tank would damage the suspension, turret ring, engine, or something else that would put the tank out of action. Tank armor is designed to resist a small very fast projectile; a very large slower projectile might cause some problems.
Just throw some gravel in the air intakes, I would assume.
Oh, sure, if you give him a stick and some gravel. Way to escalate the combat there, dude.
I’m certainly no expert - but couldn’t you effectivey disable a stealth bomber just by letting the air out of the tires? Seems to me - you wouldn’t even need the stick.
I THINK what the OP is asking is that, assuming you could actually fire off one of those ancient weapons, and you hit something (a man or a vehicle), would it even have an effect.
Assuming that’s the case, I’d say that it depends, but probably. Take a scorpion. If you hit a soldier wearing ballistic protection, my guess is that it would depend where it hit him as to how much (or if) damage it would do. In the leg, for instance, and it would hurt him as much as if it hit the leg of an ancient soldier. Catapults would be the same thing…if you managed to hit a modern soldier with a really big rock they would be just as dead as hitting an ancient soldier. The only difference is if it was a non-fatal hit a modern soldier would presumably have better access to medical care and therefore have a much better chance of surviving.
Armored vehicles would be much the same. I assume if you hit an Abrams with a big ass siege rock it would crush right through the armor, which is really designed more for shaped charges than a 500 lb or 1000 lb rock coming in from several hundred feet up. The odds of actually hitting an Abrams or any other vehicle would be pretty small, especially if the modern army was firing back, but if you DID manage to land a big rock on it it would probably do some nasty damage.
-XT
Modern soldiers wearing modern armor are no better equipped to survive a large rock hurled at them than their medieval counterparts were. Modern soldiers are just as prone to being crushed as medieval ones.
I dunno - wiki reports ranges up to 300+ meters, or a thousand feet. I’m sure modern firearms can shoot that far, but how accurate is the average grunt at these distances ?
Anyway, siege weapons were mostly effective because castles didn’t move about too much back then.
The rate of fire of larger siege machines could be as low as 1-2 shots per hour. The largest and most ridiculous ones could hope for half a dozen shots per day. And it could take quite a few shots before they got the torque just right for stones to land in the rough vicinity of the target. Which, I remind you, was a city.
I’m thinking a tank can sort of manoeuver around those parameters. Hell, a third-hand Pinto could.
Of course there were also smaller ones, flinging smaller rocks/bolts/fire pots at a shorter ranges and relatively faster rate (up to a blazing 3-4 shots per minute !).
But in this context we’re not talking about ton-and-a-half rocks any more, more like a pack of cinderblocks. 50-150 lbs or thereabouts. Even piddlier for the Roman scorpion mentionned upthread, which fired large spears.
Enough to break a wall or door over time by hammering it over and over and over, and probably also more than enough to kill or maim any sonovabitch unlucky enough to be on the receiving end - but a modern AFV can hopefully take flung cinderblocks without exploding 
Belated ETA: although I guess the question would make for fine Mythbustin’. They can load the trebuchet with half a ton of C4, I won’t mind.
I was recently reading something about the American Civil War that I feel would be relevant to this issue.
During earlier wars like the American Revolution and the Napoleonic Wars, field artillery had been a key factor in battles. Maneuvering cannons into position to fire at the enemy was a big priority.
When the civil war started, it was expected that artillery would again be a decisive issue. But it turns out artillery was pretty much a non-factor in most civil war battles. Very few casualties throughout the war resulted from cannon fire.
It was an issue of range. During the earlier wars, the main infantry weapon was the musket which had an effective range of less than fifty yards. A field cannon had an effective range of over a hundred yards. So you could set up your cannon outside of the range of your opponent’s infantry and start shooting.
But rifles were generally replacing muskets as an infantry weapon during the civil war. And a rifle could essentially shoot just as far as a cannon. So anytime a cannon tried to set up on a battlefield, its crew would come under rifle fire from the people it was trying to shoot at.
(Artillery regained its dominant position in World War I with the development of indirect fire tactics which once again put artillery out of range of effective counterfire from infantry targets.)
And this relates to the OP because it’s not really an issue of how much damage a medieval catapult could theoretically do to a modern infantry company if it hit it. Because a catapult would have virtually no chance of ever being able to launch a single round at a modern infantry company. It’s like a fight between a guy with a knife and a guy with a pistol - how sharp the knife is isn’t going to be an issue.
Do you have a cite for that Little Nemo? My understanding is that cannon during the civil war period had ranges of several thousand yards for round shot, and 400 yards+ for canister. And that they played key roles in several battles during the Civil War…plus had become highly mobile by the time of the civil war, being able to be moved around the battlefield quite handily.
-XT
I’ll see if I can dig up the reference I saw (it was in a book by Alfred Nofi).
But a stopgap, I’ll link to some pages that make the same points. They say that a civil war-era rifle (a Springfield Model 1861 which was the main rifle of the war) had an effective range of about 400 yards and a maximum range of about 1000 yards. A civil war cannon (a 12-pounder Napoleon Model 1857 which was the main cannon of the war) had an effective range with round shot of about 1400 yards and an effective range with cannister shot (which was anti-infantry) of about 400 yards. (All range figures are approximate because different sources offer different figures.)
So infantry firing at a cannon and a cannon firing anti-infantry shot both had an effective range of about 400 yards. And both could fire at approximately triple these ranges but at a loss of effectiveness.
And finally, there’s a few cites that 90% of casualties in the war were caused by rifle fire.
http://www.ehow.com/info_8028074_civil-war-weapons.html
http://www.civilwarhome.com/civilwarweapons.htm
http://www.nps.gov/archive/gett/soldierlife/webguns.htm
http://civilwartalk.com/forums/showthread.php?25891-of-casualties-attributable-to-artillery
http://www.waymarking.com/waymarks/WM9E2W_M1857_12_pound_Gun_Howitzer_Napoleon_Field_Artillery_Museum_Fort_Sill_Oklahoma
http://civilwarwiki.net/wiki/12_pdr._"Napoleon"_Light_Field_Gun
http://www.civilwarhome.com/weapons.htm
I have an image of a dramatic battle between General Bugs Bunny and Field Marshall Wile E. Coyote.
not siege weapons, seige techniques. i would say sapping still has its merits today, as does ninjutsu and even a small, concealable catapult (to launch biological weapons.)
nm
While I’m sure that’s true, if you consider the time it takes to load, aim and fire a max size trebuchet, and that aiming can’t be all that accurate without lasers and GPS, the actual overall effectiveness can’t be that great unless you have many more trebuchets than tanks.
Ballista and other spearchuckers I would agree, some of the good sized trebuchets and such tossed a mighty hefty chunk of rock. I don’t know if I would want to be at the point of impact even inside an abrams. Sure it wouldnt be an instant kill shot, but get a 200-300 pound chunk of rock flying 120 mph and even a main battle tank is gonna wonder WTF just hit them and be taking inventory. Lighter vehicles, even less cheery. Might be seriously interesting to whack something like a bradley with a 200 pound rock from a trebuchet.
A modern tank can survive impact from a train without more than losing its tracks; IIRC that happened to the Soviets once. That’s why I suggested using burning material instead; I don’t think rocks are going to cut it.