The Student Room Group
Reply 1
it's because whereas the repulsion between protons acts over a comparitively large disance, the force keeping the nuclei/neutrons together is the strong nuclear force-this acts at very short distances only, this is why, as nuclei become very large, the repulsive forces between protons acts on every proton in the nucleus, whereas the strong nuclear force only affects its nearest neighbours, hence why as atoms become larger, there is an increasing amount of neutrons needed.
I haven't revised tyhis yet so most of it is probably wrong haha, but that's more or less it. if you google it you should find out more!
Reply 2
smurfride
it's because whereas the repulsion between protons acts over a comparitively large disance, the force keeping the nuclei/neutrons together is the strong nuclear force-this acts at very short distances only, this is why, as nuclei become very large, the repulsive forces between protons acts on every proton in the nucleus, whereas the strong nuclear force only affects its nearest neighbours, hence why as atoms become larger, there is an increasing amount of neutrons needed.
I haven't revised tyhis yet so most of it is probably wrong haha, but that's more or less it. if you google it you should find out more!


woaahhh!!! clever :smile:
Reply 3
Makes sense. Cheers.
Reply 4
smurfride
it's because whereas the repulsion between protons acts over a comparitively large disance, the force keeping the nuclei/neutrons together is the strong nuclear force-this acts at very short distances only, this is why, as nuclei become very large, the repulsive forces between protons acts on every proton in the nucleus, whereas the strong nuclear force only affects its nearest neighbours, hence why as atoms become larger, there is an increasing amount of neutrons needed.
I haven't revised tyhis yet so most of it is probably wrong haha, but that's more or less it. if you google it you should find out more!


Just to add to that, the repulsive force between the protons is the electromagnetic force which has an infinite range (range is proportional to 1 over the mass of the carrier particle (in this case the photon which has no mass hence range is infinite)) and the force between the neutrons and protons is the strong nuclear force which is carried by gluons which are massive particles and hence the range is limited (to very short distances).
Reply 5
sarah_1988
woaahhh!!! clever :smile:


u is the clever 1 butt! u no it!! hahaha u stalking me?
Reply 6
yer im on ur trail so u better look out!!! :cool:
Reply 7
whehey ur online

--------------

u got an exam tuesday? holy cow after all the droppin chem etc i just realised im gunna fail maths lmao
Reply 8
yer i like the way im on the PHYSICS forum, which I have like NO knowledge of *blows dust from physics part of brain
Reply 9
rpotter
Just to add to that, the repulsive force between the protons is the electromagnetic force which has an infinite range (range is proportional to 1 over the mass of the carrier particle (in this case the photon which has no mass hence range is infinite)) and the force between the neutrons and protons is the strong nuclear force which is carried by gluons which are massive particles and hence the range is limited (to very short distances).


It says in my textbook that gluons have no mass! :confused:
Gluons have no mass, while it's the vector bosons which mediate the weak interaction which have mass. The range of the weak force, if I remember correctly, is something like 10-18m, while the strong force is 10-15m. The shortness of the weak forces range is due to the bosons having mass, so rpotter might be getting them confused.
Reply 11
Nah didnt confuse the two forces, but forgot that gluons have no mass and that since gluons and quarks are contained within the protons and neutrons you cannot use them to predict the range of the strong force. When something emerges from a proton or a neutron it must be at least a quark-antiquark pair, the lightest meson being a pion, which is a massive particle and is thus used in predicting the maximum range.
That's due to the requirement for all quarks and gluons to be "colourless", so you need either colour+anticolour or red+green+blue collection of particles. Of course you could get something like a "glueball" which is a 3 gluon cluster which would be colourless and massless, so would be able to travel further than a pion (also bear in mind there are different forms of pions).

I think there's a mildly more subtle reason for the lack of distance gluons travel, but I forget the specifics of it. The strong interaction has a potential of V=αr+krV = \frac{\alpha}{r} + kr where the linear term means you'll not get long distance interactions occuring.
Reply 13
i think gluons have no rest mass, so they only have mass when moving
But then the same applies to photons, they have momentum but no rest mass, and their range is infinite :wink: