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Forces and Newton’s Laws
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Forces• Forces are ________ (magnitude and direction)• Contact forces result from ________ ________• Field forces act ___ __ __________
Fig. 4.2, p. 84
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4 Fundamental Forces
• Strong nuclear force• Electromagnetic force• Weak nuclear force• Gravitational force
• All are ______ forces• Nuclear are _______
______ (femtometers)• Electromagnetic and
gravitational range is _________
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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
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Inertia vs. Mass
• Inertia: tendency of object to continue its _______ in the __________ of forces
• Mass: measure of object’s __________ to ________ in _______ due to force
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Newton’s Second Law
• Acceleration of an object is – directly __________ to net force acting on it– _________ proportional to object’s mass
m
Fa
1.4aF
m
This is a vector equation
xx maF yy maF 2.4zz maF
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Unit of Force, Newton (N)
2smkg1N1
lb225.0N1
slug1085.6kg1 2
US unit of mass
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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
5.42
21
r
mmGFg
Fig. 4.6, p. 90
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Weight
6.4mgw
• Magnitude of Fg acting on object near Earth’s
surface
• g is acceleration of gravity (of Earth)
8.42r
MGg E
• r is radius of Earth (RE) plus height (y) above
surface of Earth
yRr E
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Newton’s Third Law• Forces in nature always exist ___ _______• A _______ __________ force can’t 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
2112 FF
Fig. 4.7, p. 92
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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
gFn
n is ______________ to contact surface and is _____________ in origin