Defying gravity

Post by **Charles** » Sat Jun 25, 2011 9:25 pm

1. Take one cylindrical neodymium magnet (10-15mm diameter and about 30-40mm length) and a 1-2m length of 22mm diameter copper pipe
2. Holding the pipe vertical, drop the magnet alongside the pipe and measure how long it takes to reach the bottom from the top (take care not to let the magnet hit the floor as you will damage it - a cushion underneath works well)
3. Now repeat but this time drop the magnet down the centre of the pipe and measure the time taken to reach the other end.

So, what's happening?

And why might an endoscope be a useful piece of equipment as a supplement to the basic experiemnt?

Araf · Post by **Araf** » Sat Jun 25, 2011 9:45 pm

Since I left school in the early 80s, my brushes with physics have been little more than trying to make cars go faster, and watching the Big Bang Theory. Apart from guessing that there will be some sort of electro-magnetic interface between the Cu and Nd when they pass close by, I haven't a clue what you are going on about, so please enlighten us.

Araf · Post by **Araf** » Sat Jun 25, 2011 9:50 pm

Araf wrote:Since I left school in the early 80s, my brushes with physics have been little more than trying to make cars go faster, and watching the Big Bang Theory. Apart from guessing that there will be some sort of electro-magnetic interface between the Cu and Nd when they pass close by, I haven't a clue what you are going on about, so please enlighten us.

edit:

Is this something to do with the Neodymium reaching 88 miles per hour, and then travelling in time?

ade and liz flint · Post by **ade and liz flint** » Sat Jun 25, 2011 10:01 pm

Basically you're making a permanent magnet generator (I think!!).......and I'm now struggling to understand it. There will, however, due to the voltage field generated, be an electrical resistance to the magnet moving (we use pmg's to excite generators on the national grid). But I'm stumped as I don't follow the current flow

Wish I'd studied pmg design, now

Chas · Post by **Chas** » Sat Jun 25, 2011 10:51 pm

Never mind that. Tell me why an atomic clock keeps different time at the summit of Everest than at sea level. That one really blows my mind.

ade and liz flint · Post by **ade and liz flint** » Sat Jun 25, 2011 11:34 pm

Well, Einstein's General Theory of Relativity showed that clocks run more quickly at higher altitudes because they experience a weaker gravitational force than clocks on the surface of the Earth, so I guess that's the reason.

The phenomenon - called gravitational time dilation - was demonstrated by putting atomic clocks on jumbo jets and flying them at high altitudes. Just as Albert predicted, clocks flown at 30,000 feet run faster than those on the ground. The twin paradox, I think it's called.

I got to know a little about this as for really difficult customers, I had to find the accurate figure of acceleration due to gravity at their exact location just to eke a few 10ths of a % on their vibration readings, just in case....

Thank god for data sheets calculated by really clever people!

Araf · Post by **Araf** » Sun Jun 26, 2011 12:52 am

Gravity is a myth. The earth sucks.

Alpina Jim · Post by **Alpina Jim** » Sun Jun 26, 2011 1:10 am

Methinks it is time I changed to a Vauxhall or a Ford as this site is getting too techie for me.

For info my grandfather clocks wouldn't work on a jumbo jet so I think I will stay in the past as it is a lot simpler there.

ALPB1033 · Post by **ALPB1033** » Sun Jun 26, 2011 3:59 am

Is that the 3 finger rules we learned in the Physics lesson long time ago? Is it the left or right?
Yes the forum is getting more interesting now with all those theory in Physics. Great! You all

intelligent lot.

ade and liz flint · Post by **ade and liz flint** » Sun Jun 26, 2011 9:50 am

Alpina Jim wrote:For info my grandfather clocks wouldn't work on a jumbo jet so I think I will stay in the past as it is a lot simpler there.

That would be a lot of excess baggage

We dinosaurs need to stick together....down with physics! Or is that gravity again?

ade and liz flint · Post by **ade and liz flint** » Sun Jun 26, 2011 9:54 am

ALPB1033 wrote:Is that the 3 finger rules we learned in the Physics lesson long time ago? Is it the left or right?

Yep - Fleming's Left hand rule for motors, Right hand for generators. Or if you do it right, it looks like two a 2 finger salute with a touch of arthritis in the thumb

Charles' experiment is the work of the devil

Araf · Post by **Araf** » Sun Jun 26, 2011 11:06 am

I believe that if you strap a slice of buttered toast to the back of a cat, you can defy gravity.

Post by **Charles** » Sun Jun 26, 2011 12:15 pm

OK - here we go ...

A number of you are getting close with various theories but the key is to link them all together.

First thing to note is the copper has no magentic affect on the magnet - i.e. the magnet will not "stick" to the copper in normal circumstances.

However, as the magnet passes down the pipe, the magnetic field from the magnet induces an electrical current in the copper. (Right hand rule for electrical generation)

This electrical current results in a magnetic field which repels the magnet and slows the rate at which the magnet drops down through the pipe. (Left hand rule for electromagnetic induction)

The purpose of the endoscope is to view the motion of the magnet as it falls down the pipe because the induced magnetic repulsion causes the magnet to spin.

When I did this using a 3m length of pipe, the magnet took 14 times longer to fall down through the pipe than it did when dropped from the same height outside the pipe.

A great experiment that draws on a number of theories - left hand, right hand, gravity, magnetic fields etc - and can be used right through from Year 7 to Year 13 depending on the depth of detail you choose to bring into play.

Glad you like it ...

Araf · Post by **Araf** » Sun Jun 26, 2011 1:04 pm

Can you 'use' the electrical current generated in the copper, and change the rate of descent?

Post by **Charles** » Sun Jun 26, 2011 1:10 pm

The current generated is directly related to the power of the magnet - so a more powerful magnet will "fall" more slowly, as follows:

Great magnetic field induces larger current which creates greater magnetic field which results in greater repulsion force.

However, the current generated is very small indeed and this is why you need to use neodymium magnets to obtain any meaningful effect. A simple iron magnet just wouldn't be powerful enough to achieve the effect.