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Physics: Newton’s Laws of Motion Summer of Innovation Zero Robotics Newton’s Laws of Motion The Basis of Classical Mechanics 1 Introduction Who was Sir Isaac Newton? And what are his famous laws? Sir Isaac Newton is one of the most celebrated physicists of all time. He was born on Christmas Day in England in 1643. He attended Cambridge University, where he began to develop his ideas about his laws of motion. Newton made many contributions to science and mathematics besides his laws of motion. Several scientific discoveries commonly attributed to Newton include the law of universal gravitation (which we will talk about later), the law of cooling (describes how the temperature of a cup of coffee cools off in the surrounding air), and the development of calculus. Newton’s laws of motion are three physical laws that relate forces acting on an object to the motion that the forces cause. The standard unit for a force is even named after him: forces are generally measured in Newtons. 2 Newton’s Laws of Motion 1. First Law (The Law of Inertia): An object at rest remains at rest until acted on by an outside force; an object in motion remains in motion until acted on by an outside force. What it means: A soccer ball sitting still in the grass will stay still unless someone kicks it. That soccer ball will keep rolling until a force slows it down and stops it. Question: What are some forces that can stop a soccer ball? 2. Second Law: Force = mass x acceleration (F = m x a) What it means: An object accelerates when it is subject to a force. Therefore, if you know a baseball’s mass and its acceleration, you can figure out the force exerted on it. If you know the force exerted on a baseball, and the acceleration of the baseball, you can find out the mass of the baseball. 1 June 14, 2011 Physics: Newton’s Laws of Motion Summer of Innovation Zero Robotics Question: Your favorite bowling ball has a mass of 10 kg. We know that the acceleration due to gravity, g , is about 9.8 m/s2 . So, what is the force of gravity on your bowling ball if you drop it off of a building? Question: You measure that the force of gravity on your second-favorite bowling ball is 196 Newtons (N for short). The acceleration of your bowling ball due to gravity is still 9.8m/s2 . What is the mass of this bowling ball? 3. Third Law: For every action, there is an equal and opposite counter-reaction. What it means: If you exert a force on something, that force will exert a force of the same magnitude in an opposite directoin on you. Question: Imagine that you are pushing on the Great Wall of China. You push as hard as you can (a force of 1,000 N), but it doesn’t move at all. What are the forces (magnitudes and directions) exerted by you and by the wall? 3 Review • Newton’s First Law: An object’s state does not change unless acted on by an outside force; • Newton’s Second Law: Force = mass x acceleration; • Newton’s Third Law: Every action has an equal and opposite counter-reaction. 2 June 14, 2011