Transcript Chapter 4 - boykinhonors

Chapter 4
Newton’s First Law
of Motion:
Inertia
Newton’s First Law Inertia
In Fancy Terms: Every
object continues in a state of
rest, or of motion in a
straight line at constant
speed, unless it is compelled
to change that state by
forces exerted upon it.
In Plain English:
Objects in motion tend
to stay in motion.
Objects at rest tend to
stay at rest.
Inertia
Definition: the
reluctance of any body
to change its state of
motion
Examples of Inertia
Alphabet
soup
Removing tablecloth
with dishes still on
the table
http://www.youtube.com/watch?v=QbGV6qQcJrw
http://www.youtube.com/watch?v=aCqQzrPCcFM&feature=related
So Why Do
Things in
Motion Stop?
Forces
Definition: any
push or pull
Friction
Definition: the force that
acts between materials
that touch as they move
past each other
- caused
by
irregularities in
the surfaces of
objects that are
touching
- Even
very smooth
surfaces have
microscopic
irregularities that
obstruct motion
MASS
a measure of inertia
measured in kilograms

MASS AND
WEIGHT ARE
NOT THE SAME
THING!!!
Mass: quantity of
matter in an object
- independent of
location
Weight: force of
gravity on an object
- depends on an
object’s location
Mass and Weight
are Proportional but
NOT Equal
a lot of mass = a lot of weight
SI unit of mass –
kilogram
SI unit of force Newton
1 kg = 9.8 Newtons
(N)
weight = mass x
gravity
w = mg
http://www.youtube.com/watch?v=aCqQzrPCcFM
Net Force
Definition: combination
of all forces acting on
an object
The net forces changes
an object’s state of
motion
In the absence of a net
force, objects do not
change their state of
motion
Normal Force
Definition: the upward
force that balances the
weight of an object
Also called support force
Other forces:
Tension:
At equilibrium –
Tension = weight
Equilibrium
Net force = zero
Chapter 5
Newton’s
nd
2
Law
Remember:
Acceleration = change in velocity
time interval
What causes
acceleration?
Force
An objects acceleration is
directly proportional to
the net force
Acceleration ~ net force
Mass resists
acceleration
Acceleration ~ 1/mass
(inversely proportional)
Newton’s
nd
2
Law:
The acceleration produced by a
net force on an object is directly
proportional to the magnitude of
the net force, is in the same
direction as the net force, and is
inversely proportional to the
mass of the object.
In other words:
Acceleration = net force/mass
a= F/m
Net Force
Unit will always be Newtons.
1 N =
2
kg*m/s
Free Body
Diagram
Definition: Diagram
showing all the forces
acting on an object.
Applying Force
Pressure
= force per unit
of area
Measured in pascals (Pa)
2
Pascal = N/m
Pressure =
Force
area of application
P
= F/A
Pressure is increased
when surface area
decreases!
ex. bed of nails
Falling and Air
Resistance
Terminal velocity: speed at
which acceleration of a
falling object is zero
because friction balances
weight
Free Fall Explained
F =
m
F
m
Chapter 6
Newton’s
For
rd
3
Law
every action
there is an equal and
opposite reaction
All actions
occur in pairs
Action: Object A
exerts force on
Object B
Reaction: Object B
exerts force on
Object A
Newton’s Law of
Universal Gravitation
Every object is attracts every
other object with a force
that for any two objects is
directly proportional to the
mass of each object.
In other words,
the greater the masses, the
greater the force of
attraction between them
F = G m1m2
d
where G = 6.67 x 10-11 Nm2/kg2