e=mc2

[Chick]

So moving fast increases your mass too?

[Huguenot]

So yes Chick, it absolutely does!

For example Hussain Bolt is more massive (and hence on Earth he weighs more) when he's running the 100m than when he's standing still.

However, at low relative speeds (running 100m relative to standing still) it's not noticeable - because "e=mc2" means the addditional mass is calculated by dividing the relative 'running' energy (a small number) by the square of the speed of light (which is a very big number).

This is one reason why you can never quite reach the speed of light - because as you go faster you become more massive, which means you need even more energy to go faster still, which makes you more massive... and so on...

At the speeed of light, your mass would be infinite.

[Huguenot]

Today's weird one... the Moon doesn't orbit the Earth!

In fact both the Moon and the Earth orbit around their mutual centre of gravity.

If you imagine balancing a bamboo cane horizontally on your finger, the point of balance is the centre of gravity of the cane.

If you put a heavy weight on one end, and a light weight on the other end, you'd need to balance the cane with your finger closer to the heavy weight.

Because of their relative mass, the centre of gravity of a line between the Earth and the Moon is much closer to the Earth (in fact it's about 1,000 miles below the surface of the Earth.

But neverthless, both bodies orbit around this point, not around the Earth.

On another point, have you noticed how weak gravity is? You can beat it just by jumping in the air.

[Frankito]

I am a moron. No ckicks, no spectroscopy, just fact.

Ps: Brendan, your devations are hilarious.

[Salsaboy]

You mean the earh is round? I thought it was flat.

[Huguenot]

Well, it's not round, it's not even spherical. The closest mathematical comparison is 'oblate spheroid' or more accurately still a 'geoid'. ;-)

[mockney piers]

I remember years ago someone I knew, a right clever clogs saying there's no such thing as centrifugal force just a lack of centripetal.

Was he just trying to look clever or is there any truth in this.

Pst I've no idea why that phrase lodged in my head but it did.

[Huguenot]

He's quite right in one way - there isn't such a thing a 'centrifugal' force - in the sense that this is a word used to describe a force that 'pushes away' from the centre. No such force exists.

However, there must always be a centripetal force in order to have an orbit.

The appearance of a 'centrifugal force' is because of the interplay between momentum and a 'centripetal' force.

A centripetal force can be any force that attracts an object to a single 'centre' point. For example it could be gravity, or it could be tension in a piece of string being whirled around our head.

Momentum is what makes an object go in a straight line, and is calculated as mass x velocity.

The the centripetal force drags the object in towards the centre - and the compromise between this and momentum is what traces a circular direction.

Think of this like two dogs pulling a sled. Both dogs are pulling in slightly different directions, so the line the sled actually goes down is a compromise between the two forces.

http://astronomy.swin.edu.au/cms/imagedb/albums/scaled_cache/centripedal-316x300.png

So when we whirl a weight around our heads we're making very complicated and precise calculations. If we whirl it too slowly then momentum will be smaller and the weight will fall in to the centre and hit our ankles. If we whirl it too fast then the momentum will create a force greater than the strength of the string, it'll break and the weight disappear into huncamunca's shed windows.

Then we'll have a cat problem.

[Chick]

I am touch puzzled. In the sun two helium nuclei fuse to form Beryllium. Then another helium nuclei fuses with the Beryllium to form Carbon releasing more energy and so on. The combined mass of the new (fused) particles are less than the mass of all separate particles.

This missing mass is turned into energy. This is fusion.

In a bomb like the ones used in Japan the process was fission where atoms are split apart. Surely this is the opposite of fusion and there for the separate masses would be greater than the combined (fused) mass. So we have more mass after fission? So where does the huge energy of an atomic bomb come from? Both scenarios can?t be true?

[Huguenot]

Ah, the challenge is to think about mass as an energy state rather than a particle.

Atomic nuclei are made up of protons and neutrons. The number of protons in an atom is the nuclear weight.

When 'light' nuclei fuse (join together) the result is at a lower energy state than the two original nuclei. Hence they give out energy. For atoms heavier than Iron (56), the fused nuclei are at a higher energy state so they require energy putting in to fuse together, or generate energy when they split.

Hence fusion energy is created by fusing very light elements - hydrogen or helium. Fission energy is created by splitting very heavy elements - uranium and plutonium.

There will come a time in the future when the sun has turned all its light elements into heavier ones, and it can no longer create fusion energy, and that's when it dies.

[Salsaboy]

How do you know all this?

[Huguenot]

The same way you know that Armand Van Helden sang My My My - because it's fun! :)

Did you know that for the average person (around 5 to 6 feet high) standing on a beach, the distance to the horizon is about 2.5 miles?

[Salsaboy]

I did know that!

Did you know that people who are buried when they are dead are taking longer to decompose due to all the preservatives in our food these days?

[Brendan]

Ever wondered what archaeologist from some future civilisation are going to think when they dig up skeletons with silicone breast implants?

[mockney piers]

will they think they're some sort of fertility offering to the gods?

[Brendan]

Possibly. Or maybe some sort of ceremonial armour or buoyancy devices used by seafarers.

[Brendan]

Did you know in the olden days (like the 60s and 70s and stuff) they didn?t have life belts on ships because the press ganged sailors would use them to escape.

[Brendan]

The relation that the previous post has to science is something to do with the viscosity of sea water. Being non-scientifically minded though I really can?t clarify it any further myself.

[Huguenot]

It's density rather than viscosity - Archimedes principle:

"Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object."

Hence an escaping sailor will displace the amount of fluid equivalent to his own weight.

If his own volume is larger than that of the water displaced, then part of his body will be buoyed up above the water: hence he floats.

Because people are mainly water, and muscle is denser (heavier) than water, skinny and underfed sailors in the olden days displaced water that weighed less than themselves, and mostly sank.

If you add a lifevest (a large volume object that doesn't weigh as much as water), then the total volume of water displaced was less than the total volume of sailor plus vest, hence they floated.

And floating, the escaped, very slowly. Probably in a bad doggy style, as most sailors in the olden days never learnt how to swim.