Most liked posts in thread: Mythbusters busted a house

They promised that they would not air footage shot of the errant cannon blast (avoiding the possible perception that they might capitalize on their mistake.)

 

Being a bit of a military history buff, cannon balls were often fired in a manner to achieve the roll. They tended to bounce and gain a bit of speed, so when firing at a castle wall, the idea was to bounce it at the wall, rather then hit the wall directly. They were also bounced through massed groups of troops. This changed when they developed exploding cannon balls.

Jim

 

Something that heavy, tends to keep rolling and is still very destructive, even as it slows down. I doubt if it even noticed that it went through that dry wall.

Jim

 

When a moving object impacts anything it loses some energy, so a cannonball can't actually pick up speed after a bounce. Only when one object collides with another more massive moving object can it gain energy. Physics....

 

Of course the key word is "impacts"......

Here is a cool demonstration of the effects of speed from "gravity assist"....
[ Gravity Assist Simulator - Menu ]

 

Aahhh ha ha true.. But gravitational slingshots don't count in cannoneering. Well, gravitational effects do count but would be almost immeasurable for such a small mass.

 

I'm not a physics major, but if the cannon ball exited the house (slowing some naturally), struck the paved street, bounced, it would again speed on the way back down. Glancing off objects was the same effect.

Jim

 

Think of dropping a rubber ball, ...it will never rebound higher that the height it was dropped from. Just doesn't work that way....

 

Jim, you've discovered the missing link. This is what has always prevented the successful operation of the perpetual motion machine. Good show.

In all fairness, we now know the universe is expanding at an increased speed, not slowing down. So all isn't known. But typically when an object in motion collides with another object, the moving object looses energy and slows down..... Typically.... Subject to new information of course.....

 

OK, I'll concede the cannon ball.

A ram jet is a perpetual motion machine. If fuel flow is not managed it will continue to accelerate until is destructs.



Ramjets have been run from as low as 45 m/s (162 km/h)[8] upwards. Below about Mach 0.5 they give little thrust and are highly inefficient due to their low pressure ratios.
Above this speed, given sufficient initial flight velocity, a ramjet will be self-sustaining. Indeed, unless the vehicle drag is extremely high, the engine/airframe combination will tend to accelerate to higher and higher flight speeds, substantially increasing the air intake temperature. As this could have a detrimental effect on the integrity of the engine and/or airframe, the fuel control system must reduce engine fuel flow to stabilize the flight Mach number and, thereby, air intake temperature to reasonable levels.
Due to the stoichiometric combustion temperature, efficiency is usually good at high speeds (Mach 2-3), whereas at low speeds the relatively poor compression ratio means that ramjets are outperformed by turbojets, or even rockets.

 

Sorry, that not perpetual motion. The requirement that the engine requires outside fuel puts the kibosh on that.

 

I like magnets..... They are magic....
And I like donuts...... They are also magic....

 

OK, to all the more learned folks then I, I leave you with this:

While the laws of physics are incomplete and stating that physical things are absolutely impossible is un-scientific, "impossible" is used in common parlance to describe those things which absolutely cannot occur within the context of our current formulation of physical laws.

Jim