"That was forty," said O'Brien. You can see that the numbers on this dial run up to a hundred. Will you please remember throughout our conversation, that I have it in my power to inflict pain on you at any moment and to whatever degree I choose. If you tell me any lies, or attempt to prevaricate in any way, or even fall below you usual level of intelligence you will cry out with pain, instantly. Do you understand that?"
Through that quote, you can see that O'Brien has total control. He can inflict pain to Winston any time he wants, even if Winston is telling the truth. This is the power of physical control. It's kind of similar to what Saddam Hussein did to his people, the Iraqis. If anyone was caught talking about the government, they would be persecuted. The more physical control you have, the more abilities you have with that control. O'Brien can do anything with Winston if he wanted to. He can beat him, kill him, starve him, torture him, etc. This is why physical control is so dangerous, and the book does a good job showing that. After Winston goes through the period of being tortured and beaten, he realizes that that nothing is more powerful that physical pain. With the physical torture, the Party can make the humans believe in what they want them to. They can make them believe that 1+1=44 and