Selecting bigger alder seeds by their falling speed in air

Michael.

I don't want to spoil your dreams, but have you proved the basic premise behind your machine that heavier seeds fall faster than smaller ones? 500 years ago a man called Galileo Galilei reputedly dropped different size iron balls from the leaning Tower of Pisa and demonstrated to the world that they fell at the same rate. Admittedly air resistance will play a bigger part in the descent of seeds than iron balls, but I doubt the difference is so marked that it could be used for grading, so I ask again: have you proved that thicker seeds fall faster than thin seeds? I'd hate to see you waste time and money on a machine that does not work.

Cliff Coggin.

I googled for a few secs and came up with :-

as a start. This has surely been done before, no point in reinventing the wheel . In a place where I worked for many years we had masses of machinery for sorting seeds of many different grasses, clovers and cereals using blowers, screens, even iron filings and magnets (surface roughness). Cheers Don

Have a look here :

Cliff

All praise to you for your scepticism, but :-

1) Without air resistance an object will fall 5 Metres = 16 feet in the first second.

2) I just quoted the FIRST tap on the paper on the floor. It takes another 2 seconds for all of them to come down.

3) Winnowing is a well-known process for separating wheat from chaff.

Michael

Is there any proven correlation between the size of a seed and the subsequent size, many years later, of the consequent tree?

Eating the flesh of a brave man did not create bravery.

(And I wonder about the gullibility of the 21s C educated females who seem to be receptive to the presence of, "Pearl Protein" in their shampoos.)

I've looked at this link. It doesn't explain their processes, and I couldn't get their CAPTCHA ("TYPE IN WHAT YOU SEE") to accept my input.

You once did seed sorting yourself? I hear they have rather tough standards of purity for sale to the public, like "no more than ONE rat per tonne of wheat!"

Michael Bell

I wasn't personally involved in seed sorting, but it went on in our plant breeding research establishment. Our physics dep wksp was called on to design and make small bench type sorters in perspex to facilitate precise separation of various seed types. I think that you will see in my second link some of the basic principles in seed cleaning and separation. Hope this helps. Don

OK, as long as you appreciate the sometimes non-intuitive concept that heavy bodies do not necessarily fall faster then similar lighter bodies.

As an aside, the acceleration due to gravity is twice the figure you quoted i.e. 32 feet/second/second.

Cliff.

Is it proven that bigger seeds produce bigger trees?

Would a rattle box be easier? You would need to vibrate a tub and the heaviest seeds would sink?

But then are there lightweight big seeds to worry about?

In fairness he quoted a Distance 16ft I think. when I was in school some 55yrs agoI learned that S= ut + 1/2 a t squared

Don

You must have gone to the same school as did I, or else also sat the London University 'A' Level maths.

Also off the top of my head 40 years later ...

v = u + a t v^2 = u^2 + 2 a s

But you are both right

a = 32'/s^2

s after one second = 16'

'O' level physics?

I only remember the S = ut + 1/2 at^2 one - but it's about all you need to remember, you can work out the others (or even just the numbers) from it.

-- Peter Fairbrother

Cliff

At the end of its first sec> OK, as long as you appreciate the sometimes non-intuitive concept that heavy

How do you manage to insert the square symbol (little 2 after and above the v and u) It dissapears when I reply. Don

No correlation whatever.

I am interested in the seeds only as a food source. BUT seed size has an interesting ecological consequence. "Forest trees" of the "climax vegetation", ie, the state the land will eventually reach if not disturbed by man, have big seeds, think of acorns and chestnuts because they need to for their seedlings to grow in heavy shade and through years worth of leaf litter to reach earth. Such seedlings can grow in the shade of their parents. Alders cannot, they have very light seeds, so easily scattered, but their food reserves are small so they can only grow on fresh ground, they are a "weed tree". The only place where alders form the climax vegetation is birch-alder carr, where they form a long-lasting forest only because they can survive wet ground.

Michael Bell

A "rattle box"! What's that?

Michael Bell

According to my calculations the Reynolds number will be greater than 4000 i.e. fully turbulent in any pipe bigger than 2cm across at that airspeed. In a 10cm diameter pipe it would be about 20,000. So basically you can't achieve laminar airflow and I suggest it isn't an issue anyway. The Reynolds number of the flow around the seed is probably another issue but not something you can control given you need a specific air speed.

It might be easier to make if you just have a wire mesh inside the sorting tube you can chuck a bunch of them onto, turn on the motor, gradually increase the airspeed with a dial and wait for the small ones to be sucked out of the top. No shute for introducing seeds, just switch it on and off and put another batch in from the top or bottom. You could then actually grade them into batches at different air speeds if you can collect the ones that get sucked out.

Mea culpa. The distance travelled in one second would indeed be 16 feet. The result seemed so obvious to me that I didn't bother to actually calculate it. My apologies.

Incidentally, when I did O level physics some 43 years ago in London I seem to remember the abbreviation for acceleration was f, so the above equation would have been s = ut + 1/2f(t squared). Is my memory failing or was it just one of those conventions that changed over time? Just to stir up memories for the older generation, I also recall force as a result of weight being expressed in poundals.

Cliff.

The transition from laminar to turbulent flow for air in a pipe at 3 m/s begins at about 1.15 cm pipe diameter.

The pipe should be *narrower* than that for laminar flow, not larger.

You ain't going to get laminar flow.

The good news is that you neither need nor want laminar flow.

Help please!

Reynold's number for a pipe can be calculated using the formula

R = duD/m

Where d is the density (1.23 kg/m^3 for air)

u is the velocity of flow

D is the diameter of the tube (technically the hydraulic diameter, qua google if interested, but for a square tube it's equal to the side of the square) and

m is the dynamic viscosity of the fluid (~0.000018 kg/ms for air)

Flow becomes turbulent at above ~ Re = 2,100, and fully turbulent at above ~ Re = 4,000.

-- Peter Fairbrother