Phys205A_Lecture11

# Physics for Scientists & Engineers with Modern Physics (4th Edition)

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Chapter 5 Newton’s Laws Lecture 11

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Sir Isaac Newton z 1642 – 1727 z Formulated basic laws of mechanics z Discovered Law of Universal Gravitation z Invented form of calculus z Many observations dealing with light and optics z Inventor of the reflector telescope
Force z Forces are what cause any change in the velocity of an object z Newton’s definition z A force is that which causes an acceleration

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Classes of Forces z Contact forces involve physical contact between two objects z Examples a, b, c z Field forces act through empty space z No physical contact is required z Examples d, e, f z In reality, the contact forces are short range field forces
Fundamental Forces z Gravitational force z Between any objects z Electromagnetic forces z Between electric charges z Nuclear force z Between subatomic particles z Weak forces z Arise in certain radioactive decay processes z Note: These are all field forces

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More About Forces z It was noticed that for routine measurements a spring can be used to calibrate the magnitude of a force z It was noticed that stretch of the spring is proportional to the applied force: i.e doubling the force causes double the reading on the spring z When both forces are applied, the reading is three times the initial reading
Vector Nature of Forces z The forces are applied perpendicularly to each other z The resultant (or net) force is the hypotenuse z Forces are vectors, so you must use the rules for vector addition to find the net force acting on an object

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Newton’s First Law z In the absence of external forces, an object at rest remains at rest and an object in motion continues in motion with a constant velocity z But the rest and motion with constant velocity are unambiguous (relative) entities z It defines a special set of reference frames called inertial frames z We call this an inertial frame of reference
Inertial Frames z

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## Phys205A_Lecture11 - Lecture 11 Chapter 5 Newtons Laws Sir...

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