user95908: I know that the transactions stay in the block and hashed alongside few other things and that hash is stored in the next block. And I understand that if you try to tamper with one of the transactions, the hash will change and it will affect all the blocks that come after it.
However, how does a block know that its transactions have tampered with in the first place? 
Assume that block #1000 has 10 transactions.
Now, the hash has been calculated and stored in block #1001
so, if I go back to block #1000 and add one more transaction, this will change the hash and it wont be the same one stored in #1001. 
However, how the hash of block #1000 changes in the first place if it was already calculated? does this mean that the hash of each block is recalculated regularly? 

user76726: Hashes don't actually 'change'. When you add a transaction to a block you are creating another block.
It's like an author published a book and then next year printed a new edition with an extra comma in the page 36 and the fans said he released a 'new' book. It doesn't make sense for books but for blockchain every bit counts.

95908: <p>I know that the transactions stay in the block and hashed alongside few other things and that hash is stored in the next block. And I understand that if you try to tamper with one of the transactions, the hash will change and it will affect all the blocks that come after it.</p>

<p>However, how does a block know that its transactions have tampered with in the first place? </p>

<p>Assume that block #1000 has 10 transactions.
Now, the hash has been calculated and stored in block #1001</p>

<p>so, if I go back to block #1000 and add one more transaction, this will change the hash and it wont be the same one stored in #1001. 
However, how the hash of block #1000 changes in the first place if it was already calculated? does this mean that the hash of each block is recalculated regularly? </p>
 76726: <p>Hashes don't actually 'change'. When you add a transaction to a block you are creating another block.</p>

<p>It's like an author published a book and then next year printed a new edition with an extra comma in the page 36 and the fans said he released a 'new' book. It doesn't make sense for books but for blockchain every bit counts.</p>
