Be Excellent To Each Other

We have some hoops (the sort you hula with). I don't like to hula, I prefer throwing them, and using back spin, make them come back. I know how/why this works, but I find it "curious" and think of nothing, of just doing this over and over, seing how far I can make it travel, before stopping, and then coming back to me, and going past me in the other direction.

Now, my garden is essentially a patio on 2 levels, with a ledge seperating them, forming a double step type thing:




If, I stand on the bottom level, I can throw the hoop onto the top level, have it spin back, and roll on to the lower level again. Sometimes, it hits the middle step on the way done, sometimes it doesn't. I want to know the speed it needs to be travelling at (assuming it's rolling and not bouncing) as it leaves the top level to not hit the middle step.

This is the first question, I guess you are going to need some measurements, The difference in height between the 2 levels is 80cm, the step is 50cm heigh and 60cm deep, so the question is how fast does the hoop need to be travelling horizontally (V_x) to clear 60cm horizontally before dropping 30cm vertically?

Now, I can work that out myself (along with the next part), so I'll be checking answers later.

Part 2 is to work out the "general case" with the height of the step is "h", the depth of the step is "d" and the height of the upper patio is "u"


Part 3 is beyond me at the moment, so this is where I need the real help. I want to know how fast I need to throw this in the first place. I guess there are 5 variables here.

1) The height of release (r)
2) The angle of release (a)
3) The speed of release (v)
4) The RPM of the hoop at release (f)
5) The coefficient of dynamic friction between the hoop and patio

Am I missing anything? Can anyone work out some solutions on how I need to throw the hoop for it come back to without hitting that middle step? What about the "general case"?

Thanks

Malc

Are you mental?

I agree with Kalmar.

I was expecting this to be by MaliA, seeing as he's got the time for this sort of mentalism.

I guess you'd also need to know the bounciness of the hoop as well as how heavy it is. I still wouldn't know where to start with the maths, though.

You might want the radius of the hoop as well, as I guess the angular speed of the hoop at the contact point is going to be important as well. Would the mass of the hoop matter? I've a feeling it might, as momentum may well come into the equation. If you're unlucky, the angular momentum of the hoop might be a factor as well, in which case the thickness of the hoop tubing might matter, but you could probably model it as a "perfect hoop" with all the mass concentrated on the outside edge to make that easier.

I view physics with suspicion.

Like New Zealand, I'm aware it exists, but if I don't bother it, then it won't bother me.

Don't forget the perfect hoop also must be a perfect circle, have no imperfections and the outside edge mass concentration must be a linear depth all the way round the hoop.

Errmm... Get an Xbox 360?

That's a good point - you want a perfectly circular hoop that's totally rigid, so that it remains circular on impact, other wise you'll get the size of the contact point varying over time.

You'll want to ignore air resistance as well, otherwise you'll get bogged down in differential equation hell.

Why not go and do the experiments, take the measurements and work it out from there?

Heh. Spot the scientist who wrote his hypothesis last!

I have one, Spinning hoops > Xbox 360

Malc

Practical experiments take all the fun out of Physics...

Empiricist.

Might just have to get one and give it a go now!

Yeah, I forgot about the initial bouncing...

As for using measurements to establish my own equation, I don't have any equipment, and can't guarentee that I can control the RPM or release velocity of the hoop precisely (and getting a machine to do it for me would take the fun away)

Malc

In order to understand how a car functions, a biochemist took it to pieces and examined each part, noting how they interacted with those around them. Over time, he began to understand how the car functioned.

In order to understand how a car functions, a geneticist went to the factory each day, and blindfolded a worker. he then sat on the hill overlooking the factory, eating his lunch and watched the results. From this, he was able to work out what bits did what.

You need to construct such a machine. I recommend a child's bike, with a child pedalling it, the rear wheel attached to a belt which drives two discs spinning to throw the hoop.

Jesus, do I have to do ALL the thinking for BeeX?

I recommend introducing a fat man into the path of the hoop.

Your face is a fat man with a hoop.

We'd have also accepted "Your mum's a fat man with a hoop"

Or "you're a fat man with a hoop", if I've been following forum trends correctly.

Ooh, I haven't noticed the the 'your mum _______'s about in the wild.


Oh, now your just spoiling us

The possibilities...

Your Mum's a fat man.

Your man hoop is a fat mum face.

Your mum's fat hoop is a man with your face.

You're your mum.

Your you're your mum.

Your fat face is a mum hoop, man.

Your you're your mum's face

And.... Relax!

I'm shocked.

You should be ashamed.

Right, who's got this hoop, then?

Huh?



It's Malc's hoop, and he's welcome to it.