If a glass is dropped from a phenomenal height?
Would it completely shatter to dust. My 10 year old asked this question after noticing that the glass fragments were much smaller from a drinking glass dropped from an upstairs window, to a glass just knocked from a dining table onto the floor (he has an incredibly clumsy mother!) Thoughtful question, but for a mum who’s supposed to know everything its got me stumped! please help x
KoolKermit
on February 8th, 2012
You have an amazingly perceptive 10 year old!
I think the answer depends on whether or not the glass is dropped in the atmosphere. If you went up in a plane and threw a glass out the window, the glass would accelerate towards the earth but the air would slow it down until it reached a terminal velocity, after which it would stop accelerating and continue to fall at that speed. That effectively limits the amount of energy the glass will have when it impacts the earth. If the speed at which the glass impacts is high enough, the glass will have so much energy that it will shatter into very small pieces, possibly even as small as dust. But if the impact velocity isn’t high enough, then it will probably shatter into many pieces, some of which are larger. The distribution of the sizes will depend on a number of factors, including the size and shape of the glass, internal resonances within the material, imperfections in the glass, and which part of it hits the earth first.
There was an article a few years ago (I believe it was in The Economist) about scientists who smashed things and then analyzed the size distribution of the shattered pieces. What a fun profession. Apparently one can tell a lot about the original shape of an object by how many pieces one has of different sizes. There’s a similar article I found here, talking about fragmentation studies into — believe it or not — how spaghetti breaks: http://www.sciencenews.org/articles/2005... .
Assuming you could spare the glasses and keep people and pets from being injured, your child could probably do a pretty nifty science fair experiment on this when he’s old enough. It’s a bona fide problem in physics today.
PoPCorn
on February 8th, 2012
Does depend on the type of glass, and it doesn’t matter what height you drop it, if its dropped higher then say 50ft it would fall at the same speed if you dropped it at 30,000ft. I think maybe a light bbulb would probably be closest turning to dust. Did you know that glass is actually the slowest moving liquid on the planet?
Orchid
on February 8th, 2012
I’d say not, I know that any falling object has a terminal velocity. It reaches a speed and won’t go any faster.
I believe it’s about 20 storeys high that terminal velocity is reached. I wouldn’t expect the glass to turn to dust, just small pieces.
oddperson
on February 8th, 2012
Likely the glass would never turn to dust if dropped from a great height. It is much harder to make small pieces than big pieces. Have your ten year old break a piece of dry spaghetti into smaller and smaller pieces. The glass shards will get smaller and smaller when dropped from greater height but not break up into dust which would likely require a grinding operation (which crushes the pieces). Although there is more energy added to the glass the farther it falls, due to air resistance there is a ‘terminal velocity’ and a limit to the available energy.
Hippie
on February 8th, 2012
This assumes that a falling object will continue to accelerate cotinuously until it hits the ground. That’s not true. The terminal velocity (maximum speed of an object) is determined by it’s drag which is a component of it’s crossection, shape, and to some extent it’s composition.
Therefore at some point, it’s maximum speed would be reached, maybe 200 miles an hour, which I don’t believe is enough to shatter a glass to dust. Very small pieces maybe, but not dust. To do that you would have to accelerate the glass to at least the speed of a bullet.
SlightlyBitter
on February 8th, 2012
Interesting Q. This depends on what is the terminal velocity of the glass tumbler. When things are dropped from a height, in Earth’s atmosphere, they will continue to accelerate until the resistance of the air rushing past is equal to the force of the gravity pulling them downwards. This is called ‘terminal velocity’ and it will depend on how heavy an object is and how streamlined it is. Obviously a feather has a different T velocity to a lead sinker. If you dropped a feather and a sinker together on the Moon, which has no atmosphere they would both hit the ground together. Impossible to say for an individual glass what it’s TV would be, but it would not likely be fast enough to make a glass dissappear in a puff of dust. You might achieve this result however if you fired a glass at a concrete surface from a high power cannon.
CrispApple
on February 8th, 2012
it depends on how strong the glass is and how high will be the place whre you will drop the glass.
but if the height is so high that it is almost lightyears in distance then whatever knd of glass available today will surely be completely shatterede to dust or even smaller particles
Sunflower
on February 8th, 2012
The type of glass will make a difference, but no, there is no height a glass can “drop” from where it will just become dust.
For places like Earth, where there is an atmosphere, the air will produce drag and the glass will reach a terminal velocity at some point. Being dropped from higher than needed to achieve terminal velocity won’t add any more energy to impact.
Now, if a spaceman were to throw a glass at a black hole, at some point that glass would disintegrate, but not even dust would be left.
Seashells
on February 8th, 2012
The faster the speed it impacts at the more it will ‘atomise’.
More energy is imparted so it breaks apart more.
Heres a video to demonstrate the point –
http://www.youtube.com/watch?v=W9cNf73cQ...
That cloud of dust is not the wall.
FunnyFish
on February 8th, 2012
IANALY has given a very good answer. I also agree that you seem to have a very bright child there.
ChickenLicken
on February 8th, 2012
i supos theres a maximum shattering thigy as the glass reaces its maxium velocity it possably can so theres probable a smallest size of glass shard can be but yeh id say it would be smaller with a greather height as more gravataionl potental enerygy is stored and a greater energy transfer in needed making more sound more heat so it would makle sense to shatter more as more heat energy would be realesed