Transcript Physics 321 - BYU Physics and Astronomy

Physics 321
Hour 1
Course Introduction
Course Components
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Course Outline
Prerequisites: ODEs, Mathematica
Reading: Due before lecture
HW: Due MWF - see schedule on Learning Suite
Take-home Tests: Due every other Thursday
Midterm Exams: In the Testing Center
Final Exam: In Class
Course Components
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Reading: 5%
Homework: 10%
Take-home Tests: 40%
Midterms: 25%
Final: 20%
HW & Takehome Tests
Physics 321
Hour 1
Newton’s Laws of Motion
Before Newton
What is the natural motion of an object?
• Greeks – without force, motion stops
• Kepler – straight lines (earth→heavens)
• Galileo – circles (heavens →earth)
• Descartes – matter and motion are conserved
Before Newton
How do we understand collisions?
• Descartes – conservation of motion
• Huygens – motion = mass x velocity
• Leibniz – vis viva = mass x velocity2
Newton’s 0th Law
The quantity of motion is the measure of the
same, arising from the velocity and quantity
of matter conjointly.
= Huygen’s definition of motion
Newton’s 1st Law
Every body continues in its state of rest, or of
uniform motion in a right line, unless it is
compelled to change that state by forces
impressed upon it.
= Descartes’ idea of natural motion
Newton’s 2nd Law
The change of motion is proportional to the
motive force impressed, and is made in the
direction of the right line in which that force
acts.
= A way to measure/define force
Newton’s 3rd Law
To every action there is always an equal
reaction; or, the mutual actions of two bodies
upon each other are always equal, and
directed to contrary parts.
• Forces are binary
• Momentum is conserved instant by instant
• Forces add as vectors
Newton’s Laws and Measurement
What do we have to measure to verify/apply
Newton’s laws of motion?
What is mass, space, time?
How have our ideas of mass, space and time
changed since 1687?
Do Newton’s Laws Work?
How could we tell if forces are really are binary?
Are they binary?
Two examples: charges and a bat, Lorentz force
What would be necessary for forces to be
conserved instant by instant?