To understand why this is the case, we only need to look at the famous equation, e=mc². Since energy is directly related to mass, adding energy to a system affects the mass the following way: m=e/c². So if we were were to add 1,000 joules of potential energy to a spring, its mass would increase by 1,000 / c² or 1.113 × 10^-14 grams.

I didnt know that.

And thats the kind of stuff that makes me say WHAAAAAAAT?!!?

Please prove this by conducting practical experiments rather than your maths wizardry.

Please also note, that in olden times (pre hack probably), they’d burn people for saying things like this

It would be easy to check.
Weigh a spring, weigh a clamp.
Clamp the spring in the clamp and weigh that.
Any difference?

But hot air is lighter than cold air. This e=mc² chap has some more thinking to do.

Good luck finding scales that can measure 1,000 / c² or 1.113 × 10^-14 grams Einstein.

Please also note, that in olden times (pre hack probably), they’d burn people for saying things like this

Read on my phone, I thought you had written that they would bum people for that.

But hot cold air is lighter has more mass than cold hot air.

FTFY 😉

does the spring weigh the same as a duck?

Read on my phone, I thought you had written that they would bum people for that

They probably did that too, but think they may have been banned!

But how would you weigh a compressed spring without also weighing what was compressing it?

When you weighed the whole system the weight would be the same

what happens if you put it on a conveyor belt though – that is the real question you must answer !

“hot air is lighter than cold air“

No, hot air is less dense than cold air. The same amount (ie number of molecules) of hot air would have a teeny tiny weeny bit more mass than it did at a lower temperature.

Bamed for bumming what ever next

You don’t need any fancy maths to prove this.
Put a spring on your scales and weight it, now push down on the spring to compress it, and record the new weight.

I tried that Ian, but the weight when compressed wouldn’t stop fluctuating.

I thought my full sus weighed more over the bumps.

I tried that Ian, but the weight when compressed wouldn’t stop fluctuating.

The problem is with your experimental protocol. What you need to do is use a weight to compress the spring, rather than pressing down on it by hand.

heat is energy yeah? so if we heat up the spring does it weigh more?

a baby would be perfect for this DD

If I look at elastic or latex I can achieve the same effect by stretching it – ie. it will weigh less when stretched?

This may explain why if I fill a thick latex balloon with helium so it stretches the latex really, really thin it rises in the air – its weight has gone down so much?

I am banned from using the kitchen scales to weigh him JY 😀

Good luck finding scales that can measure 1,000 / c² or 1.113 × 10^-14 grams Einstein.

DealExtreme will have ’em…

DrP

..it will weigh less when stretched?

Back of the class, dunce!!

DrP

Back of the class, dunce!!

why dat den?

surely I’m adding energy by stretching it?

Yup..; energy = mass = weight, so it would get heavier…..

Simple mistake – I left my first wife* because she thought the earth only pulled her ‘down’, and refused to believe she pulled the earth towards herself with an equal force relative to her mass…the bufoon…

DrP

(*this may not be true)

heat is energy yeah? so if we heat up the spring does it weigh more?

Yes

If I look at elastic or latex I can achieve the same effect by stretching it – ie. it will weigh less when stretched?

You’re adding energy by stretching it so it has more mass…

ah, yes, of course.

*dons dunces cap*

It looks good on you…

DrP 😉

While I actually agree that the spring does increase in mass. How are you going to measure it?

If you compress it with a weight, then that weight has lost gravitational potential energy by compressing the spring. So it will have lost mass.

0.00000000000001 grammes heavier.

It’s ‘cos C is a universal constant.

Easy.
Compress it by wrapping wwaswas’s elastic band around it.
Hence both spring AND band gain potential energy – double whammy….

DrP

Does it make any difference in mass if the spring (compressed or otherwise) is on a conveyor belt?

Similarly a spinning top weighs more than a non-spinning one. If anyone knows what a spinning top is any more…

If the spring were made of Titanium the effect would be betterer.

So if compressed springs weigh more does that explain why hardtails with rigid forks are lighter than full-suss bikes?
.
The same is true of batteries, the dead ones are lighter than the charged ones, need something better than kitchen scales to show this though.
.
Also, I asked the question that as heat is energy does hot food contain more calories than the smae food when cold? The answer is yes, only a little bit becasue of the heat itself, most of the difference is down to the fact that hot food is easier to digest and so more of the calrories from the food itself are released.

ononeorange – Member

Does it make any difference in mass if the spring (compressed or otherwise) is on a conveyor belt?

if it’s moving, it has kinetic energy…

“While I actually agree that the spring does increase in mass. How are you going to measure it?“

You’re not.

See, “c squared” is A Very Big Number, hence in everyday life the change in mass of anything is jeff-all.

The equation starts getting interesting when you look at kinetic energy of a mass whose velocity approaches the speed of light.