How malloc() and sbrk() works in unix?

Question

I am new to UNIX, and I am studying some of UNIX system calls such as brk(), sbrk(), and so on....

Last day I have read about malloc()

Answer 1

sbrk() function increases the programs data segment allocation by specified bytes.

malloc(4096); // sbrk += 4096 Bytes
free();       // freeing memory will not bring down the sbrk by 4096 Bytes  
malloc(4096); // malloc'ing again will not increase the sbrk and it will use 
                 the existing space which not result in sbrk() call.