![]() ![]() When my talk was over, I received an applause, but the applause was longer and louder than I had expected. As he told historian David Zierler last year, as his talk ended there was a particularly enthusiastic eruption of applause. Projecting his slides on a transparency, ’t Hooft gave what he thought was a pretty good talk. The presentation-perhaps not accidentally-coincided with the announcement of the Nobel Prize. In 1999 Gerard ’t Hooft of Utrecht University in the Netherlands was invited by a colleague and friend to give a talk in Bologna, Italy, about gravity and quantum physics. The following stories illuminate how Nobel Prize recipients can be, at heart, ordinary people who are thrust into extraordinary circumstances. Others describe the subsequent congratulations and celebration. (AIP publishes Physics Today.) Some focus on how the researchers discovered they had been awarded the prize. Many stories from physics Nobel laureates and their colleagues are recorded in the oral history collection compiled by the Center for History of Physics and the Niels Bohr Library & Archives of the American Institute of Physics. As a result, they often have fascinating tales to tell about the day their lives changed forever. But for all the fanfare and fame that come with the award, the laureates are only human. The Nobel Prize in Physics shines a spotlight on a select group of scientists. Two months earlier, Kosterlitz received an unexpected call while on the way to get lunch. Michael Kosterlitz (left) receives the Nobel Prize in Physics from King Carl XVI Gustaf of Sweden at the Stockholm Concert Hall in December 2016. Therefore, the rocket engine actually works better in space than here on Earth.J. However, in space since there is no atmosphere, the exhaust gases can exit much easier and faster, thus increasing the thrust. On Earth, air tends to inhibit the exhaust gases getting out of the engine. This thrust depends upon the speed of the exhaust gases and the mass of gas being expelled each second, sometimes called the burn rate in pounds of fuel per second. We call this push, the thrust of the rocket, i.e. This momentum change of the gases gives the rocket the "push" to go forward. ![]() ![]() As the exhaust gases go in one direction, the rocket goes in the other to keep the total momentum of the system constant. In a similar manner, a rocket moves in space because the gases are given momentum as they are expelled by the rocket engine. Although things are now moving, the total momentum of the gun-cart system has not changed. Thus, one momentum is positive and one is negative, making the total change (their sum) zero. The magnitude of the momentum of the bullets equals the momentum of the cart but the directions are opposite. If the gun is fired, the bullets go in one direction while the cart recoils in the other. Now the momentum of various parts of the system may change, but the total momentum must always be constant.Ĭonsider a machine gun mounted on a lightweight cart. Simply stated the conservation law says that in a closed system (one without outside influences) the total momentum of the system remains constant. Momentum is defined as the mass of an object times its velocity. The law of conservation of linear momentum is very important in physics. The rocket works because of the law of conservation of linear momentum. Therefore, the force of propulsion must be something other than friction. However, a rocket in space has nothing to push against. The train pushes on the track and the car pushes on the road because of friction between the wheels and track or road. The force of friction propels ordinary objects such as cars and trains. It is fairly common for people to have a misconception regarding the principle on which a rocket operates. ![]() Just what is the difference in a propeller and a rocket driven device. A rocket could have also moved the plane forward but rockets were not yet invented. They designed a propeller that pushed on the air to make their plane move forward. The Wright brothers probably never thought about flying in space where there was no air. How does a rocket work in space where there is no air to push against? September 2002
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