[bigtim (OP)]

"Why do Brazil nuts float to the top of muesli?"

I don't necessarily want an answer since it must be my own work, though some hints/starters would be nice.
In case you wondering, this is an assignment for my degree course. Yes, i know, what a crazy question, but I must attempt to answer it.
Like  I say, any hints/starters will be appreciated.

Cheers

[Heliotrope]

By float do you mean float in a bowl of milk ?
Or do you mean why do the brazil nuts come to the top of the packet when you shake it ?

If it's the first one then it's probably down to density.
If it's the second then it's down to the fact that all the smaller bits in the muesli can fall down the smaller gaps between the larger objects. They can get underneath the bigger ones so the tendency is for the smaller items to go to the bottom and the bigger ones to come to the top.
It's all due to grain size.
You can try it with a golf ball in a packet of Rice Krispies. Takes a while but the golf ball always comes to the top.
Or you could try a hazelnut in a bowl of uncooked rice.

[daveshorts]

It might be interesting to see how the smaller things are moving, it is often useful to see how the individual objects are moving, so possibly make some identifiable and video the experiment. You may have to think about how you are going to be able to see them, and without the use of an MRI machine (I know some people usin them for this type of thing) what container will allow this.

An important principle in science is to simplify a problem as far as you can possibly beyond the point of it still being interesting, understand that and then try the  more difficult thing. This may involve making your own muesli, or muesli model.

[Heliotrope]

Nah, you don't need an MRI machine for this.
A glass jam jar, a handful of rice and a couple of peanuts will do.
If you want to get sophisticated you can use two glass sheets placed 10mm apart. Seal up the edges but leave the top open.
Fill it part full of small spherical objects and drop a few larger spheroids in there then fill most of the rest up with the small stuff.
Then hold the sides, put the bottom of it on your knee and jiggle your leg around a bit.
You'll soon see what happens.