When I'm alone practising my whole weight is going through and nothing is blocking it, but then when it comes to my piano lesson or when I'm performing I always tend to block my weight going through onto the keys by lifting up shoulders and have tension in my arms. Any suggestions or even exercises on what I can do to stop this happening?
You must know when you need to tense (contract) muscles and when you don't. For the moment of key depression you're going to have tension, after that just flop (though keep the wrist level). Beware of any technique that requires constant tension. Try my blog instead - https://keyboardclass.blogspot.com . A much easier read!
Arms sliding off the keyboard!? I suppose that goes with your danger-of-falling-off-the-piano-stool notions?
There's a reason why surveyors don't build bridges that are only anchored to anything at one end.
You have to wonder why we're built with arm free at one end too. Jeez, one lousy design in your book!
The shoulder is only free if it's supported at the other end. Otherwise something has to hold it there. An arm cannot "hang" outstretched- unless it hangs between TWO points.
And if the arm 'hangs' in your sense, fixed at both ends, it ain't much use.
Are you interested in actually thinking about this?
No, in the same way I'm not thinking how pigs could fly. Neither hypothesis has a shred of evidence for it.
Hold out a sword horizontally for a minute.
Then try and play the piano with it!
If you're not interested in thinking about what determines possibility, don't get involved in discussion.
You can't call your rude delusional comments discussion. They're blatant ad hominem attacks. So let's leave it there.
Hold out a sword horizontally for a minute. Then rest the end on something and see if it's any less effort. You'll find it's substantially less.