Mirror ball drop

[bruce]

Bruce - Isaac Newton's work was indeed magnificent, and laid the path for much of what we know today, however his work did not include the effect of air resistance and terminal velocity, nor did it consider the motion of anything other than a particle with a central centre of mass and negligible size.

 

Perhaps - but the basic principles are valid. If you look at Newtonian mechanics in the strictest sense - ie stuff that Newton himself developed - then you have a point. But classical mechanics, can easily accomodate effects such as air resistance, terminal velocity etc etc. Stokes' Law, if I remember correctly...

 

For these reasons, I don't believe that it is entirely valid to use Newtonian Mechanics in a real world context - it is fine as a guideline, but for the kind of accuracy required here is clearly not appropriate.

<{POST_SNAPBACK}>

 

In this case, I'd argue precisely the opposite! This is a case where simple Newtonian methods are perfectly valid - a sphere falling through air, in an environment where it never reaches anywhere near its terminal velocity. Terminal velocity in this case would be over 100 mph, achieved after falling for several seconds and seveal hundred metres. We are talking about an object falling perhaps 4 or 5 metres. The difference between the calculated values and the measured values in our case would be negligible!

 

Bruce.

[Nick Evans]

And Newton's mirror ball, without air resistance, would accelerate faster than the actual piece, therefore Newton's model would require a more substantial structure than that which is actually required. Hence Newton's calculations add a small safety factor.

 

Why complicate things when you don't need to? If Newton got it so wrong, how come you can still use his experiments today and see your experiment match the theory to 2 decimal places?

[J Pearce]

In most cases Newton's Laws will overestimate how strong the structure should be. Which is not a bad thing.

 

Plus, I've spent a year learning laws of physics and I'm bloody well going to use them.

[Jivemaster]

Newton's laws give a great method of mathematically modelling the stunt, then a real life test with no-one in the room tests the calculations and their inplimentation, then check the safety factors, then review the safety of allowing the performers near, risk to ... and risk from them. then consider whether the stunt can go ahead.

 

Sometimes it's BETTER to assume the stunt is dangerous then eliminate hazards, reduce hazards, revise the method, and produce a SAFE working practice before it gets to confrontation with the Prod/Director etc.

[Ben...]

(veering gently off topic...)

 

Bruce - Isaac Newton's work was indeed magnificent, and laid the path for much of what we know today, however his work did not include the effect of air resistance and terminal velocity

Better than that, Newton's mechanics provided a system where you can include however many effects you want using a simple set of rules. Newton's equations accurately describe the mechanics of the world around you to a very high precision - it's only when you get really (really) big, extremely small or very fast that they stop working so well.

 

...nor did it consider the motion of anything other than a particle with a central centre of mass and negligible size.

But, fortunately, it went on to show that all rigid bodies can be treated as a particle with a centre of mass, and that soft bodies can be considered as integrals of point bodies.

 

In most cases Newton's Laws will overestimate how strong the structure should be. Which is not a bad thing.

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...that depends on the model you use. If you approximate things you'll get approximate answers. The standard mechanics formulae taught at A-Level are not all there is to Newton's mechanics.

[Nick Evans]

If you approximate things you'll get approximate answers. The standard mechanics formulae taught at A-Level are not all there is to Newton's mechanics.

But they are more than adequate for this exercise.

 

Why complicate things?

[Ben...]

If you approximate things you'll get approximate answers. The standard mechanics formulae taught at A-Level are not all there is to Newton's mechanics.

But they are more than adequate for this exercise.

 

Why complicate things?

<{POST_SNAPBACK}>

I was trying to defend the good name of Newton - I'm not saying you should be doing things the complicated way :** laughs out loud **: