Why does the character jump all the time to different heights?

Question

Unity

void Update()
    {
        if (Input.GetKey(KeyCode.Space) & isGrounded)
        {
            rigidbody2D.AddForce(transform.up * jumpForce, ForceMode2D.Impulse);
        }
    }

A character can jump, say, 4 unit cells, and the next jump is already 8, why is that?

Answer 1

Let's say you pressed the space bar 2 times and during this time managed to go through 1 FixedUpdate frame, it will count it as 2 jumps