What happens inside an extension charmed object?

Question

From Pottermore - Extension Charms we get this quote:

These spells not only increase the interior dimensions of objects, while leaving the outer ones unchanged, they also render the contents lighter.

My question is more based around where and when the objects are lighter and if they experience this themselves.

For instance it is obvious that when lifting an Extension Charmed item filled with heavy objects the entire collection of objects is lighter, at least from the outside.

So when a person enters an ECed (Extension Charmed) tent does that person become lighter inside of the tent or just to forces outside of the tent? Equally are objects inside an ECed item lighter whilst you interact with them when you are inside? I.E picking up a bed whilst inside a tent as oppose to picking up the tent with the bed inside. Or would it all be relative? So that when you enter the tent you become lighter but also weaker so everything would seem just as heavy as normal.

It seems obvious to me that a tent (basically a huge bag) would render it's contents lighter including people.

• Would accept a physics answer

Answer 1

Weeeeellllllll we do get to see a little of Harry's experiences inside Perkins's charmed tent - and, actually, there are loads of examples in Deathly Hallows but I've got The Goblet of Fire with me, so:

He picked up the dusty kettle and peered inside it.

Harry Potter and the Goblet of Fire - p.74 - Bloomsbury - Chapter 7, Bagman and Crouch

Hermione and Ginny went into the next tent, and Harry and the rest of the Weasleys changed into pyjamas and clambered into their bunks.

Harry Potter and the Goblet of Fire - p.106 - Bloomsbury - Chapter 9, The Dark Mark

There's no mention of a period of adjustment where they underestimate their own strength. Mr Weasley doesn't lift up the kettle and smack himself in the nose with it, it being so much lighter. They can clamber into their beds without pulling them down on top of themselves. Nor, for that matter, do the beds topple over as they toss and turn in their sleep, or anything like that.

So it looks to me like everything remains in proportion. There's no suggestion (and surely Harry, entirely new to all of this would notice it) of things feeling different when you're inside a charmed object. Whether the things get lighter but you get weaker, or whether everything's the same with you, but different to someone outside, I don't know.

Obviously, to fit in, you'd have to shrink, or it would have to kind of grow around you, in either case, that would seem to require things to be kept relative. If you shrink, obviously your muscles will be smaller and you'll be weaker. Obviously if your surroundings sort of scale up to normal size around you then ... well they're normal size as far as you're concerned.