Transcript force - RPSpencer

•GALILEO:
Since he
experimented to
get _________
for his
conclusions,
he is considered
to be the
father of
____________
physics.
• Things in motion tend to
___________________;
they do NOT tend to
____________________
ON THEIR OWN.
• In fact, Galileo figured
out that it TAKES
___________ to make
something slow down or
stop. The usual force is
(he discovered):
________________.
• So in fact, GALILEO figured out
the principle behind what we call
__________________
NEWTON’S 1ST LAW
• An object at rest
tends to stay at
rest, and an object
in motion tends to
stay in motion in a
______________
at _____________
unless acted on by
an outside _______
force.
INERTIA refers to
Newton’s 1st Law
• Inertia is a measure of an object’s
_______________ to _____________ in
state of motion.
• The word inertia comes from the Italian word
for “_________________.”
• Inertia is ________________PROPORTIONAL
TO ___________ ONLY.
• INERTIA IS NOT _____________!!!
IT IS A
___________________________!
What is the difference
between mass and weight?
MASS is
•the amount of
_____________
in an object.
•Mass does NOT
___________,
regardless of
location.
•Mass is
measured in kg.
•It is a scalar.
WEIGHT is
–the pull due to
__________.
–Weight
CHANGES due
to location!
–Weight is a
___________!
–It is a vector.
inertia…
• If you are floating
around in space
outside the space
shuttle, and go up
to it and give it a
kick, what will be
the results?
What is force?
•A
_________________.
• A _____force is the leftover
(or unbalanced) amount of force after
you add up all the forces acting in a
certain direction. (examples in a sec…)
• Only NET forces cause
______________________!
• No net force means ____________.
Newton’s 2nd Law:
• The acceleration of a body is
directly proportional to the ___
_____ on it, and inversely
proportional to the _____.
• This means Fnet = ma, but is
usually just written _________
FORCE UNITS
• Think of Newton’s 2nd law:
F=m a
• N = kg m/s2
• Since mass is in kg, and a is in
m/s/s, or m/s2, F or Forces are
measured in kg m/s2.
• That is the SAME as a Newton, or N.
F = ma
100N = 100kg X 1.00m/s2
a = F/m
1.00m/s2 = 100N / 100kg
…Newton’s 2nd Law…
• This makes sense…the
more massive something
is, the ________ it is to
accelerate. And the
more force there is, the
_______ something will
accelerate.
• Zero net force
means _______
acceleration.
F = ma
W = mg
• A 2 kg mass accelerating
at 3 m/s2 has how much
net force on it?
• If you weigh 150
pounds, your mass is
about 68 kg. (1 kg =
2.2 lbs.) What is your
WEIGHT in Newtons
here on Earth?
SOLUTIONS
• A 2 kg mass accelerating at 3 m/s2 has
how much net force on it?
• ___________________________
• If you weigh 150 pounds, your mass is
about 68 kg. (1 kg = 2.2 lbs.) What is
your WEIGHT in Newtons here on
Earth?
• ____________________________
F = ma
a = F/m
• A force of 16 N is pulling on a 2 kg
wagon. If there is no friction, how fast
is the wagon accelerating?
• If the wagon above is going at a
CONSTANT VELOCITY with the 16N
pull, how much friction is there?
• A force of 16 N is pulling on a 2 kg
wagon. If there is no friction, how fast is
the wagon accelerating?
• _____________________________
• If the wagon above is going at a
CONSTANT VELOCITY with the 16N
pull, how much friction is there?
• _______________ ! If going
constant velocity, acceleration is
_______, & net force is ________ so
all forces are BALANCED (equal) in
any 1 direction.
Newton’s 3rd Law:
• Every action [force] has
an equal and ________
reaction [force].
• There are NO single
______________. They
always occur as an
___________pair.”
• For example, you touch
the table with 1N of
Force, it touches you
back with 1N of Force
____________________
(not a little later!).
• Newton’s 3rd Law says that an action
reaction pair would be hands pushing
on barbell, barbell pushing on hands.
• Then HOW can the barbell be
ACCELERATED upward?
• What OTHER action reaction pairs are
involved?
More on Newton’s 3rd…
• If you smash the wall with your
fist with 80 N of force, the wall
will hit you right back with 80 N.
• But what if you hold a piece of
paper in the air and try to hit it
with 80 N?
If the paper …
• cannot support or hit you back with
80 N, can YOU really hit IT with 80
N?
• If the paper can only hit you back
with 5 N, what happens to the other
75 N from your punch??!
HINT:
Force of friction
•Opposes
____________
•Occurs between
_____________
in contact
FOUR TYPES
OF FORCES
• Right now we think there are 4
different types of forces. Einstein
was working on a “unified force
theory” before he died, and others
continue that work today,
believing that there is really only
one type of force.
The four types of forces
(weakest to strongest)
are:
1. Gravitational
2. Weak [Nuclear]
3. Electromagnetic
4. Strong [Nuclear]
Gravitational force…
• Is the
____________
of all the
forces, but acts
over the
____________
distances!
You are pulling and pulled by _____
__________ IN THE __________!!!
___________
forces…
• Are the forces that act due to
electron configuration in atoms
• These forces are responsible
for the ________________ or
characteristics of elements,
compounds, and materials
• This force
makes paint
stick to a wall,
makes
diamonds
extremely hard,
makes gold
malleable,
rubber stretchy,
water a bipolar
molecule, etc.