# Forces and Newton's Laws Forces and Newtons 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 _________ Newtons 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 objects __________ to ________ in _______ due to force Newtons Second Law

Acceleration of an object is directly __________ to net force acting on it _________ proportional to objects mass F a m F ma 4.1

This is a vector equation Fx ma x Fy ma y Fz ma z 4.2 Unit of Force, Newton (N) 1 N 1 kg m s

2 1 N 0.225 lb US unit of mass 2 1 kg 6.85 10 slug The Gravitational Force Newtons 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 m1m2 Fg G 2 r Fig. 4.6, p. 90 4.5 Weight Magnitude of Fg acting on object near Earths surface

w mg 4.6 g is acceleration of gravity (of Earth) ME g G 2 r 4.8 r is radius of Earth (RE) plus height (y) above

surface of Earth r RE y Newtons Third Law Forces in nature always exist ___ _______ A _______ __________ force cant exist The force F12 exerted by object 1 on object 2 is equal in _________ but opposite in _________ to the force F21 exerted by object 2 on object 1 F12 F21

Fig. 4.7, p. 92 Force Pairs & the Normal Force TV resting on table attracted by Earth (Fg) Pair: ______ attracted to ______ (Fg) 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 Fg n is ______________ to contact surface and is _____________ in origin