Transcript Newton`s laws

Inertia!
• Kinematics- Study of motion of objects
– How objects move
• Dynamics- Study of motion of objects
WITH FORCES
– Why objects move
• Mass- Amount of Matter that an object has
– Units: Kilogram (kg)
– Symbol: m
– 1 kg = 2.2 pounds
• Inertia- a property of all matter
– Tendency of object to maintain its present
state of motion
• Newton’s 1st law of motion:
• Or Galileo’s law of inertia:
• Whichever:
– An object at rest will remain at rest,
and an object in motion will remain
in motionat a constant speed and in a straight
line,
unless acted upon by an external,
unbalanced force
• A Force is a push or a pull
• A Force is what changes the
motion of an object
• Direction of the Force matters, so
it is a vector quantity

– Symbol: F
– Units: Newton (N) mass times
acceleration
•Kg*m/s2
Types of Forces
• Gravity :is a force of attraction that exists
between any two masses
• Friction: force resisting the relative motion
of solid surfaces
• Applied: a force that is applied to an object
by a person or another object.
Types of Forces cont…
• Tension: force that is transmitted through a
string, rope, cable or wire when it is pulled
tight by forces acting from opposite ends.
• Air resistance: frictional force that acts
upon objects as they travel through the air.
• Normal: support force exerted upon an
object that is in contact with another stable
object.
• A Free Body Diagram is a picture of the
object, with all Forces that are acting on it.
• The Forces are drawn outward from the
center of the body
• They can show you the Direction (and
magnitude) of the TOTAL Force
• If you can’t draw, then just make a
dot!
• And draw all the forces on the
FU
object.
• Label them!!!
FLeft
FRight
wt
The Total Force
• At any one time, an object usually has 2 forces
acting on it. Think of the rope in a Tug-Of-War:
• More specifically, the center of the rope
• If 2 forces are going in opposite directions, then
one must be thought of as positive,
• and the other as negative.
• The acceleration
that an object

experiences
FTot is
adirectly

proportional to the Total
m
forcem
exerted on1itN  1 kg  1
2

sec
• That F
acceleration is also
Tot
m
  proportional to the mass
inversely
a
of the object

 is what
• A Total Force
Fchanges
 a motion of an object
Tot  mthe
F
g
m
• One of the most common forces we
deal with is weightG
• It is the Force due to gravity
• To put it into terms of Izzy’s 2nd:
– The acceleration
due to gravity is
G
directly related to the Force due to
Mass
and
Weight
are
gravity
F  mg
NOT
and inversely related to mass
(which is not due to gravity)
the same thing!!!!
Statics
• When all forces on an object
Balance
m


FTot  0 - N a  0
2
sec
1. How many forces are
T
on the sign?
2. Draw the Free Body
Diagram
FN
Joe’s
Crap Shak
FG
Skydivers:
• If Roy jumps out
of the plane,
neglecting air
resistance, he
will have only
one force on him
– Weight!
FTot
Skydivers:
• Only an idiot would jump
out of plane without a
parachute!
• You just have to be
completely nuts to jump
with a parachute!
• Since a parachute
depends on air
resistance, now we
have to consider it!
FTot
Skydivers:
• At first, weight is
more than the force
from air resistance
• After a bit of time, air
resistance balances
weight
– If forces are balanced,
velocity is constant
– That’s Terminal
Velocity!
• Then the Parachute
opens!
FTot
Skydivers:
• Now you have the
same weight, but
much different
surface area!
• Air has more
material on which to
push
• Crazy Roy slows
down!
FTot
Skydivers:
• Eventually, Air
Resistance doesn’t
push as hard
• Terminal Velocity
occurs again, just not
as much as before
• Lucky for Crazy Roy,
anyway!
FTot