Transcript Force Mass Motion

Force
Mass
Motion
How can I get the
catapult to hit the
target the first
time?
Aristotle’s View
Two types of motion:
Natural motion - what an object
“naturally wants to do”
Violent motion - what an object has to
be forced to do
Aristotle’s View
In order for a “normal” object to move at
constant velocity, something must be
pushing on it. When the pushing stops,
the object (perhaps gradually) comes to
a stop.
Galileo’s View
Realized that the classical view of
motion did not recognize the role of
friction
If left to themselves, moving objects
don’t slow down.
Newton’s First Law
Whatever an object is doing, that’s what
it wants to keep doing.
If left to themselves, objects will keep
doing whatever they’re doing.
Newton’s First Law
Objects at rest tend to stay at rest.
Objects in motion tend to stay in motion.
Newton’s First Law
If there is no net force on an object,
the object won’t accelerate.
Acceleration is not the same as
motion…it is a change in motion!
Newton’s First Law
The converse is also true:
If an object is not accelerating, then
there is no net force on it.
What is an “object”?
Anything made of matter is an
“object”.
What is a “force”?
A force is an interaction between 2
objects involving a push or a pull.
Forces are vectors - they have a
direction in space.
Common units of force are:
pounds, Newtons, or dynes.
What is a “net force”?
The net force on an object is the vector
sum of all of the forces that push or pull
on the object.
Adding vectors
“no net force on an object”
means:
either there are no forces on the
object, or:
the forces that push or pull on the
object all cancel exactly.
“object won’t accelerate”
means:
the object:
–won’t speed up.
–won’t slow down.
–won’t change
direction.
Newton’s First Law can be
stated:
If no forces push or pull on an
object, or if the forces that do push
or pull on it all cancel exactly, then
the object will not speed up, slow
down, or change direction.
Inertia
In other words…
Objects tend to remain at rest until you hit
them
AND
Things keep on doing whatever they are
doing until something else hits them.
Inertia
Newton’s First Law says that objects do
not accelerate spontaneously.
This property of matter, which causes
objects to resist acceleration, has been
named “inertia”. Coin & cup…
Newton’s First Law is often called the
Law of Inertia.
Friction
Friction is a force that arises due to the
relative motion of two surfaces.
– Two solid surfaces - sliding friction, rolling
friction
– A solid and a fluid - air resistance
– Two fluids
– Paper and book…
Friction
The direction of the friction force always
opposes the relative motion of the
surfaces.
Friction
The amount of sliding friction depends
on:
– The condition (smoothness/roughness) of
the surfaces
Newton’s Second Law
Force is proportional to mass
F = ma dropping balls…
Newton’s second law
Gravity is constant for all falling objects
The force of the fall depends on mass
MythBusters Link- dropped bullet vs. a fired
bullet
http://dsc.discovery.com/videos/mythbusterssimultaneous-bullet-release.html
Indian and the Canoe
http://library.thinkquest.org/3042/java/linear_dem
o.html
*Answer questions and complete table on handout.
Newton’s third law
For every action
there is an equal
and opposite
reaction
Momentum is
conserved
If time check out…
Roller coaster Physics: It is your mission to design the coaster so that you can
achieve maximum thrills and chills without crashing or flying off the track (unless that痴 how you like your
coaster to work!).If you accept this mission you must decide on a number of factors. You are responsible for
setting the controls for the height of hill #1, hill #2, the size of the loop, the initial speed of the coaster, its
mass, the gravity at work and the amount of friction on the track.
http://www.funderstanding.com/coaster
OR
Momentum:
http://www.glencoe.com/sites/common_assets/scien
ce/virtual_labs/E24/E24.html