Forces and Newton’s Laws

Forces Forces are ________ (magnitude and direction) Contact forces result from ________ ________ Field forces act ___ __ __________ Fig. 4.2, p. 84

4 Fundamental Forces Strong nuclear force Electromagnetic force Weak nuclear force Gravitational force All are ______ forces Nuclear are _______ ______ (femtometers) Electromagnetic and gravitational range is _________

Newton’s First Law An object moves with a constant velocity, unless acted on by a ________ net force. –Velocity is a vector: magnitude and direction Net force: _______ _____ of all forces exerted on object

Inertia vs. Mass Inertia: tendency of object to continue its _______ in the __________ of forces Mass: measure of object’s __________ to ________ in _______ due to force

Newton’s Second Law Acceleration of an object is –directly __________ to net force acting on it –_________ proportional to object’s mass This is a vector equation

Unit of Force, Newton (N) US unit of mass

The Gravitational Force Newton’s Universal Law of gravitation: Every particle in the Universe attracts every other particle with a force that is: –Directly proportional to the product of the particles’ ___________ –Inversely proportional to the _______ of the __________ between them Fig. 4.6, p. 90

Weight Magnitude of F g acting on object near Earth’s surface g is acceleration of gravity (of Earth) r is radius of Earth ( R E ) plus height ( y ) above surface of Earth

Newton’s Third Law Forces in nature always exist ___ _______ A _______ __________ force can’t exist The force F 12 exerted by object 1 on object 2 is equal in _________ but opposite in _________ to the force F 21 exerted by object 2 on object 1 Fig. 4.7, p. 92

Force Pairs & the Normal Force TV resting on table attracted by Earth ( F g ) Pair: ______ attracted to ______ ( F g ’ ) But a = 0, so another force is present. n is _________ force of table on TV Pair: normal force of _____ on _____ ( n ’) Fig. 4.8, p. 93 n is ______________ to contact surface and is _____________ in origin