Bill_Marsden,

I like the spinning idea, since the mass isn't evenly distributed there should be a difference in moment of inertia.

Yes, but how do you implement the method? Ratch

 

The Electrician,

Release both balls simultaneously to roll down an inclined plane. The ball with the lower moment of inertia (the titanium ball) gets to the bottom first.

Right you are. Each ball starts out with the same potential energy. When they reach the bottom of the incline, they will have both rotational energy and translational energy. The ball with the highest distribution of mass away from the center of rotation will have the highest rotational inertia, and therefore hog more of the available potential energy. So the gold ball will be traveling slower when it reaches the bottom of the incline. Ratch

 

triggernum5,

Yea, but what if these balls are planet sized?..

Let's be somewhat practical. They could be large or small, but they have to be manipulable. Ratch

 

Only problem is, without any measurement devices you cannot be sure the plane will be uniform enough to guarantee the same path is travelled by each ball, (or that the balls are subjected to the same parameters during travel atleast..) You need a pretty dang perfect incline to achieve repeatable results with a degree of error that doesn't squalch the feasibility of the test.. So since most labs have spoons, and you'd need tools/measurement devices (that could substitute for the spoon) to build a rig in the field.. You'd be much smarter to just tapa tapa tapa..

 

You can use a VLF metal detector to distinguish the metal type. Basically, you have a transmitter and a shielded recieve coil. The amplitude and phase compared with the transmitted wave will give you both the amount of eddy current flowing and the conductivity of the metal.

You would need to calculate or easily test the response in order to be able to identify them in the future.

Steve

 

scubasteve_911,

What if I specified glass and balsa wood? Ratch

 

then you'd get nothing at all
I didn't read through the entire thread, just mainly the original.

So, you want some sort of universal ball-material classifier?

You absolutely require many different methods working together to do this. When I design a wood detector, are you going to ask me "What if I give you pine and cedar balls?"

Good luck,

Stephen

 

Seems to me any ball small enough to man-handle to the top of an inclined plane would be small enough to spin. I want my spoon back.

 

scubasteve_911,

So, you want some sort of universal ball-material classifier?

Nope, I described the geometry and the fact that you are dealing with a light and heavy density material. The method The Electricial described works only for that set of materials and geometry.

You absolutely require many different methods working together to do this. When I design a wood detector, are you going to ask me "What if I give you pine and cedar balls?"

No one asked anyone to design anything. Ratch

 

look at the original post, you stated a problem, people came up with solutions, then you modified the problem. You aren't provoking thought, you're causing annoyance.

 

Ratch are you asking a question to which you do not know the answer, or are you presenting a problem for others to solve? If it's the first, then you really should cut back on jeering everyones contributions with these sarcastic off the point "what if" scenarios if they have nothing to do with the main issue. You specified the spheres contained metal, why are you now saying "what if they are wood?" You will get better help with questions that are both detailed and maintain continuity.

 

scubasteve_911,

look at the original post, you stated a problem, people came up with solutions, then you modified the problem.

I pointed out that some of the solutions were unnecessarily complicated and elaborate or would not work if the materials were not metal. The problem was not necessarily to determine whether the materials were metals, but which ball has the highest density of materials. If I elaborated too much on that point, it would too easily point to a solution anybody could guess at.

Ratch

 

m4yh3m,

Ratch are you asking a question to which you do not know the answer, or are you presenting a problem for others to solve? If it's the first, then you really should cut back on jeering everyones contributions with these sarcastic off the point "what if" scenarios if they have nothing to do with the main issue. You specified the spheres contained metal, why are you now saying "what if they are wood?" You will get better help with questions that are both detailed and maintain continuity.

How can you say I don't know the answer when I gave it out and explained it on post #22 of this thread? Did you not read the answer? As I said in the previous answer to scubasteve_911, I could not state the problem in too much detail because it would point to a answer too quickly.

Ratch

 

How about starting off these questions by letting people know they are "brain teasers" or "riddles" so they don't get frustrated trying to help solve a problem for what is not an "I don't understand please help!" situation.

 

m4yh3m,

How about starting off these questions by letting people know they are "brain teasers" or "riddles" so they don't get frustrated trying to help solve a problem for what is not an "I don't understand please help!" situation.

Sorry, I thought that everyone knew that it was a brain teaser. I will note that next time I pose a problem.

Ratch

 

You know, with enough care in replication of position, leaning something against each, and seeing which begins to move with less force might yield more accurate results Macgyver style than rolling them outright.. But I think Mac has a spoon on his Swiss Army knife..

 

scubasteve_911,



I pointed out that some of the solutions were unnecessarily complicated and elaborate or would not work if the materials were not metal. The problem was not necessarily to determine whether the materials were metals, but which ball has the highest density of materials. If I elaborated too much on that point, it would too easily point to a solution anybody could guess at.

Ratch

I gotcha, sorry for getting a bit rude. Just next time remember to clarify the problem / your intentions, it sucks when you think you have a good idea then to be told it isn't that great for no reason.

 

he said same weight..but weight and mass aren't the same... gravity will always pull down at the same speed... but i would think deceleration of a denser item would take longer. it's been a while since i've had physics

I do know a pound of gold is heavier than a pound of lead

then u must agree if i said a pound of gold is heavier than a pound of cotton?

shudn't it be 1 cm cubic of gold is heavier than 1 cm cubic of lead?

 

One is made of gold and hollow, other is not hollow and made of titanium. Both balls are identical in size and weight, and covered with a shell made of non-transparent, electricity/heat/cold non conducting material. Find a way to determine which ball is made of what, without damaging the shell (you are not allowed to burn it, place in liquid, etc.) and without using any external measurement equipment.

Ratch

the hollow one will bounce when being drop and produce different sound pattern...

 

I pointed out that some of the solutions were unnecessarily complicated and elaborate or would not work if the materials were not metal.

Well, so what? The original post stated that the balls were made from gold and titanium.

The problem was not necessarily to determine whether the materials were metals, but which ball has the highest density of materials.

The problem was not at all to determine whether the materials were metal. As I already stated, that information was given.

If I elaborated too much on that point, it would too easily point to a solution anybody could guess at.

OTOH, as ScubaSteve and I pointed out earlier, you could have given a bit more information as to what sorts of tests were allowed or not allowed, without having to go to the extreme of an exhaustive list. IMO, the best problems are the ones where all the information is given up front.
Mark