# 2force - Sir Isaac Newton Born 4 Jan 1643 in Woolsthorpe Lincolnshire England Died 31 March 1727 in London England The key to understanding

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1 Sir Isaac Newton Born: 4 Jan 1643 in Woolsthorpe, Lincolnshire, England Died: 31 March 1727 in London, England The key to understanding Newton's ideas about motion is to investigate the description of "force" and "mass." The main idea is that "forces cause accelerations," and, that the amount of acceleration depends on the "mass" of the object. Simply, a force is the reason why an object might accelerate.

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2 Newton’s First Law Every object continues in its state of rest or of uniform speed in a straight line unless it is compelled to change that state by a "net force" acting on the object . This doesn't say that every mov ing object has a "force" acting on it. This doesn't say that a stat ionary object has no forces acting on it
3 Inertia All objects resist changes in their state of motion. Mass (m) as a Measure of the Amount of Inertia. Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion.

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4 Example: Passengers move forward when the driver breaks the bus. Example:
5 Example: Newton's 2nd Law enables us to compare the results of the same force exerted on objects of different mass . Newton’s Second Law The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The direction of the acceleration is in the direction of the applied net force.

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6 Example: First and second laws
7 Example : To stop a 2000 kg car moving at 14m/s in 2.0s requires an average breaking force, F = ma = (2000kg)(-14m/s)/(2s) = -14000 N. Example : Two forces, F 1 =45.0N and F 2 =25.0N act on a 5.00kg block sitting on a table as shown. What is the horizontal acceleration (magnitude and direction) of the block? F 1x = F 1 cos(65.0) = 19.0 N F x = m a x Σ F x = F 1x - F 2x = 19.0 N - 25.0 N = (5.00kg)a x a x = -1.2 m/s 2

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8 Newton’s Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first .
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## This note was uploaded on 01/02/2012 for the course PHYS 1149 taught by Professor Bala during the Fall '11 term at Northeastern.

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2force - Sir Isaac Newton Born 4 Jan 1643 in Woolsthorpe Lincolnshire England Died 31 March 1727 in London England The key to understanding

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