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lecture_tan9

# lecture_tan9 - Key Concepts Lecture 9 Describing Motion...

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Key Concepts: Lecture 9 Newton Newton’s Laws of Motion More on Kepler’s Laws Newton’s Law of Universal Gravitation Newton 1642-1727 Only child, posthumous son of an illiterate yeoman born prematurely - sickly as child raised by maternal grandmother as a child he built clocks & sundials practical joker Trinity College, Cambridge University at 18 studied mathematics & astrology encouraged to study physics by Barrow University closed in 1665 due to plague Invented calculus, studied gravity, optics Barrow resigns & gives Newton his post at Cambridge Describing Motion • Position • Velocity – Rate of change of position (speed & direction) • Acceleration – Rate of change of velocity 2 examples of acceleration: Newton’s Laws of Motion Law I: Law of Inertia A body at rest or in motion at a constant velocity along a straight line remains in that state of rest or motion unless acted on by a net outside force. Takes next logical step beyond Galileo’s definition of inertia ( tendency of a body to keep moving after all forces stop acting on it ) Uniform motion is just as natural a state for a body as being at rest

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Laws of Motion Law II - The Force Law The acceleration (a) due to an applied force (F) is in the same direction as the force & is proportional to the strength of the force & is inversely proportional to the object’s mass (m) The units of force are chosen so the constant is 1. So we write a = F/m To have acceleration there must be a force Force & acceleration always work in the same direction Given the same force, a more massive object accelerates more slowly than a less massive one Force=Mass xAcceleration a ! F / m a = constant x F /m constant = 1 a = F/m We can write this as F = m a Examples of the Second Law • Friction – Hockey puck on ice vs. on a street Impact of a bat on a baseball – The bat imparts a force to the ball and sends it flying in the opposite direction Question? A ball is attached to a string and I spin it abound my head in a circle – Is the ball accelerating?
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lecture_tan9 - Key Concepts Lecture 9 Describing Motion...

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