Physics 1
Dynamics Notes
How Many Ways Can You Think of
to State Newton's First Law
(the Law of Inertia)?
BHS
-> Mr. Stanbrough ->
Physics -> Mechanics
-> Newton's Laws ->
Newton's First Law -> this page
- "Every object continues in its state of rest, or of motion in
a straight line at constant speed, unless it is compelled to
change that state by forces exerted on it." (Hewitt, Paul G.,
Conceptual Physics, Second Edition, p. 28)
- "Things tend to keep on doing what they're already doing."
(Hewitt, p. 29)
- An object at rest tends to stay at rest, an object in motion
tends to stay in motion.
- Objects resist accelerations.
- Objects don't like to accelerate.
- Left to themselves, objects don't speed up, don't slow down,
and don't change direction.
- It requires an unbalanced force to change the velocity of an
object.
- An object at rest will stay at rest unless an unbalanced force
acts on it. An object in motion will move at constant velocity
unless an unbalanced force acts on it.
- If an object has a constant velocity, then no unbalanced
forces are pushing on it.
- A force on an object tends to change its velocity. If no force
pushes or pulls on an object (or if the forces on the object
cancel each other out) then the object's velocity stays the
same.
- No unbalanced force means no acceleration.
- No force means no acceleration.
- If no forces act on an object (or if all of the forces that do
act cancel each other out), then the object will not:
- speed up
- slow down
- change directions
- "Whatever an object is doing, that's what it wants to do." -
Professor Julius Sumner Miller
- Objects don't accelerate unless "forced" to.
- Objects don't change their velocity by themselves.
- If an object is not accelerating, then either:
- no forces are pushing on it, or
- all of the forces that are pushing on it balance each other
exactly.
- If you see an object at rest, or moving in a straight line at
constant speed, then you can conclude that either no forces are
pushing on the object, or (more likely) all of the forces that are
pushing or pulling on the object cancel each other out.
- Consider a body on which no force acts. If the body is at
rest, it will remain at rest. If the body is moving with constant
velocity, it will continue to do so. (Halliday, Resnick, &
Walker, Fundamentals of Physics, 5th Edition; p.
82)
- If no force acts on a body, we can always find a reference
frame in which that body has no acceleration. (Halliday, Resnick,
& Walker, Fundamentals of Physics, 5th Edition;
p. 82)
- If nothing pushes on you, you won't accelerate (or decelerate,
either).
- If you leave an object at rest, it will "stay put" forever
unless something pushes or pulls on it. If you start an object
moving, it will keep moving at the same speed in the same
direction forever unless something pushes or pulls on it.
- "The velocity of a free body is constant in time." (David
Layzer, Constructing the Universe, Scientific
American Library)
- "Objects continue to do what they are doing unless acted upon by
an outside force." - Jeremy Raver
- If Fnet = 0, then a = 0.
- If there is no net force on an object it is in equilibrium,
and vice versa.
- Objects made of matter have inertia.
- Inertia is a property of matter.
- Objects like to be in equilibrium.
- "Things keep doin' what they're doin' 'til you mess with 'em." -
David Charles Schaller
- If an object doesn't interact with any other objects, it won't accelerate.
- "A body at rest will remain at rest until 8:45 PM the night before the science-fair project is due, at which point the body will come rushing to the body's parents, who are already in their pajamas, and shout, 'I JUST REMEMBERED THE SCIENCE FAIR IS TOMORROW AND WE GOTTA GO TO THE STORE RIGHT NOW!'" - Dave Barry
BHS
-> Mr. Stanbrough ->
Physics -> Mechanics
-> Newton's Laws ->
Newton's First Law -> this page
last update November 2, 2007
by JL
Stanbrough