static variables in multithreading

Question

I found that declaring a variable as static makes no sense in Multi-Threading. I assume that, this is because of every thread has its own

Answer 1

Because first part of question is already answered, I will try to answer on second question.

I know that static variables should be used within synchronized block. but why?

Because if you don't use atomic, operations with variables are not atomic. That's why you should block variables while working with them. But in real world, you can use volatile keyword, that will guarantee you, that threads will have actual values of variable.