BEIJING - Chinese President Xi Jinping on Monday had a telephone conversation with U.S. President-elect Donald Trump. Xi congratulated Trump on his election and said that in 37 years since China and the United States established diplomatic...

One Pulley If you have a single wheel and a rope, a pulley helps you reverse the direction of your lifting force. So, as in the picture below, you pull the rope down to lift the weight up. If you want to lift something that weighs 100kg, yo...