0 Members and 1 Guest are viewing this topic.
The condition under which a body is, literally, free to fall under the influence of the local gravitational field with no resistance to its acceleration.
The colloquial use of the term covers falling through air resistance but it isn't strictly correct.
Just pull the column out of the way, sideways. Or push the weight off the column (probably easier to do!)
I'm in strict pedant mode today.
1. It still isn't free fall. The acceleration of the object will depend on its shape.
2. An explosive charge will have some upward force component and the debris and expanding gas beneath the object will have a different composition from the air under the other mass, so its behaviour will be different depending on the nature of the trigger event.
3. Where did the second mass come from? Something must have been holding it up before the explosion!
any aerodynamic properties
You will recall (had you been awake in Physics 101!) that s= ut + 0.5at2where s = distance, t = time and a = accelerationin vacuo, say s = 15 and a = 32. u=0, so 0.5 x 32 x t2 = 15, t= sqrt(15/16) = 0.9682 secondsv = u + at, so speed on hitting the ground = 32 x .9682 = 30.98 ft/sec. This is a long way below the terminal speed of a cannon ball so you would find it difficult to measure the difference between in vacuo and in air arrival times. However ...sorry, you cannot view external links. To see them, please
REGISTER or LOGIN shows some surprising results, including a sharp decrease in drag at relatively high Mach numbers - but it's all very dependent on the shape of the projectile, so you can't easily extrapolate from a cannon ball to any other lump of iron.In respect of Quoteany aerodynamic propertiesI repeat that a 100 lb glider will take a lot longer to hit the ground than a 100 lb cannon ball.
I think we have agreed on the definition of free fall.
No need for animations, but I'm impressed with yours.
The problem is that the "control" does not move in sync with the "clamp" unit, so it's very confusing. And I still don't like the idea of the "control" appearing ex nihilo - even worse when it appears and moves at random times! Once you have established the free fall time from the clamp, you can just refer to the number without having to replicate the test in each animation.
For what it's worth, I have a PhD in experimental physics, about 45 years' experience in various branches of engineering for medical radiation, and enough studies in aviation to fly myself to work. But this stuff is all covered at school level!
Impressive drawing! My artistic skills stop at machine blueprints and printed circuits.
The sync is a little better but still jerky and "A then B",which doesn't make the point. Not sure what program you are using to generate the animation but if I wanted to show this in Powerpoint I'd group the two objects together so they fall as one. After all, that's what Galileo demonstrated.
If I was presenting this in a lecture, I'd start with just the clamp release, then show a slide of the clamp and the "control" with the explanation that from now on we will be keeping the idealised object on the right as a constant reminder of what happens to an object in free fall. Then you can develop all sorts of scenarios on the left.
My dad swore he saw an Indian exam paper that said "you may ignore the weight of the elephant..."
And just one more niggle - though this may be the point you are trying to make - the mass of the objects is irrelevant. In free fall, all objects fall at the same rate.
... I'm sure I could make them much smoother using a site that permits more images per animation, but then, it would take me considerably longer to produce them.
I'm waiting with bated breath for the moment when Bin Laden's face appears in the smoke, or the lizard changes into George W Bush.
So far, so obvious. I'm sure this is leading somewhere. Can we cut to the chase?
Difficult to comment without seeing the actual video, but a lot depends on the internal structure of the building.
Consider a simple brick-built shed with a pitched, trussed roof (I've just rebuilt one!)
If you had a gas explosion near the base of the building, the bricks would blow outwards but the roof would remain fairly intact as the trusses can withstand tension as well as compression, so the entire roof would fall like a parachute. Now blow away the roof tiles (which will happen after a few seconds' descent, because shingles are only intended to support forces from outside) and the "parachute" approximates to your dense weight.
I can envisage a building where progressive failure in the lowest part of the walls becomes explosive as the upper part and roof accelerates downwards, with the lower walls bursting like an aneurysm under the increased internal pressure. In its simplest form the model is a cylinder whose walls are supporting a weighted piston. Once the cylinder begins to give way, the piston starts to compress the air inside and bursts the walls, which then allows the piston to fall. The total outward aerostatic force on the walls, once the building starts to collapse, equals the weight of every part that is no longer supported. Very few buildings (apart from nuclear power stations and the like) are designed to withstand outward force.