A speeding bullet.

Merecat · Post by **Merecat** » Sat Apr 25, 2015 8:41 am

Experiment #2
It stopped, I didn't

Blackal · Post by **Blackal** » Sat Apr 25, 2015 8:45 am

You are Magnus Pyke, and I claim my £10 !

Sometimes a theory has to be proven - empirically................

Al

Tapio · Post by **Tapio** » Sat Apr 25, 2015 11:58 am

Corvus wrote:
Tapio wrote:On a rolling wheel, in the point of contact with tarmac, the wheel has 0 speed.
The forward moving vector, and the rotational vector cancel each other out.
We can try to apply this principle to a tyre on the road but it fails on lots of levels. Deformation and slip spoil it. A billiard ball on a flat measuring table is very close to perfection, but even that will have tiny anomalies.

The principle seems to hinge on a straight line and a point. Perfect geometry. But yet again I seem to reach the same conundrum. Because a line, by definition, has zero width then what portion of the circle has a zero vector value in contact with the perfectly horizontal surface? Zero portion! So all of the circle must experience some vector value, no matter how minuscule!

This could drive you nuts. No wonder the ancient Greeks wandered around in their dressing gowns all day!

Yes, but that goes for all laws of nature. There's friction, there's losses, there's drag etc. Not to mention poorly calibrated measuring devices.
But if you're a greek and draw circles in the sand, such petty things doesn't bother at all.

Here's another one: the rolling wheel is also rotating around the point of contact! Dressing gown on

Boxermed69 · Post by **Boxermed69** » Sat Apr 25, 2015 4:37 pm

Merecat wrote:Experiment #2
It stopped, I didn't

Corvus · Post by **Corvus** » Sat Apr 25, 2015 4:53 pm

Pssst. Oi. Boxermed. Ask to see his data logging. That'll scupper him.

Corvus · Post by **Corvus** » Sat Apr 25, 2015 5:05 pm

Tapio wrote:

.......Here's another one: the rolling wheel is also rotating around the point of contact! Dressing gown on

So the wheel is an infinite series of infinitesimally thin (zero wide) levers, all following one another after an infinitesimally small (zero wide) number of seconds of arc have passed?

I'll say one thing about them there ancient Greeks. For sticks in the sand, they came up with some stunning geometry. One of them even measured the circumference of the earth to within a few percent of the modern figure, armed only with a stick.

Tapio · Post by **Tapio** » Sat Apr 25, 2015 5:58 pm

Yes, that was a pretty good way to describe it. The point of contact is called...ehh... it's called momentancentrum in swedish. Don't know what it's called in english. Momentary center?

oyster · Post by **oyster** » Thu Nov 05, 2015 4:39 pm

Just seen this : http://www.iflscience.com/physics/what- ... posite-way
It proves that fired from the rearward facing gun, a bullet looses velocity equal to the forward motion. When fired from a forward facing gun, it must gain the velocity of the firing platform. Glad that's cleared up.
Bugger, now I will have to think up a new conundrum.

Corvus · Post by **Corvus** » Thu Nov 05, 2015 8:34 pm

oyster wrote:Just seen this : http://www.iflscience.com/physics/what- ... posite-way
It proves that fired from the rearward facing gun, a bullet looses velocity equal to the forward motion. When fired from a forward facing gun, it must gain the velocity of the firing platform. Glad that's cleared up.
Bugger, now I will have to think up a new conundrum.

Good post.

Good thread. Enjoyed it. Thanks.

Corvus · Post by **Corvus** » Fri Nov 13, 2015 6:29 am

Different topic, but one of youz may know the answer!

Does light have a distance limit?

andy griff · Post by **andy griff** » Fri Nov 13, 2015 8:52 am

It's definitely winter ....

Corvus · Post by **Corvus** » Fri Nov 13, 2015 9:48 am

andy griff wrote:It's definitely winter ....

Brace yerselves. ..