4). I Types of Forces :
Forces are vectors
2 categories of forces
-
contact forces
-
field forces
·
normal force F
-
force exerted at interface between 2 objects (surface that exists between (objects.
-
it points perpendicular (normal) to that interface.
equal to objects weight but not
-
an always
Tension Fr
-
force that acts along length of stretched
spring , rope ,
etc :
magnitude is at every point along rope .
-
same
-
this is true even if direction of rope changes.
·
friction (i
-inherently a resistive force.
-
always points opposite to motion (or intended motion)
Spring Force Esp
-
if stretched
, spring pulls inward ,
if compressed ,
it pushes outward .
thus it is a restoring force
-
-
this force is given by Hookes law : Esp = -k*
K is it describes how stiff spring
spring constant ; is
-
-spring acts opposite to displacement causing force C-sign
Section 4 . 2
gravitational force Fg on object is its weight
mass (m) of object is the amount matter in object
.
the weight is
given by
Eg ma =
is still
g = -9 81 .
m/sy
we measure m in kg
the unit of force is the newton (N) ,
where N =
Kg m/s
.
mass is same wherever object is
weight depends on strength of gravity
.
, Section 43 .
We can write a force in component form :
F FxX = +
Fyy +
Fzz
the net force on an object is sum of all forces :
Fnet [F F F Fz=
=
,
+ + ...
Fne+ X = F
,x = F, x +
E2X
Fnety SFiy =
= F
, y
+
Ezy
if we have the components ,
then we can find magnitude & direction.
every force is exerted
by one object another object.
·
on
the net force object only includes forces on that object.
on
acting
·
We ignore any internal Forces , only considering external forces .
Free-Body Diagrams FBD
·
draw object of interest as a point .
We draw each force from object
acting Vector point away
·
on
object as a
ideally the of correspond to strengths of but don't need to be too concerned
, lengths arrows should forces ,
w/ this.
EX person
pushing box
.
across a frictionless surface
FN
A
· Ex or
↓
Eg
Section 4 4 .
Newtons First Law
A in motion atconstant
body at rest will remain at rest ,
and a
body in motion remains speed
in a like unless is acted upon by force .
straight ,
a external
so, no net force ,
no
change in t
only net force matters not individual forces
Cindividual forces balance
,
-
mathematically : V =
constant as long as Fnet =
Also called law of inertia
inertia describes of an to resist to its motion.
tendency object changes
·
Newtons Second Law Acceleration : of system directly proportional to the forces inversely proportional to the
mass .
Fret
=
Enet or
= m
Forces are vectors
2 categories of forces
-
contact forces
-
field forces
·
normal force F
-
force exerted at interface between 2 objects (surface that exists between (objects.
-
it points perpendicular (normal) to that interface.
equal to objects weight but not
-
an always
Tension Fr
-
force that acts along length of stretched
spring , rope ,
etc :
magnitude is at every point along rope .
-
same
-
this is true even if direction of rope changes.
·
friction (i
-inherently a resistive force.
-
always points opposite to motion (or intended motion)
Spring Force Esp
-
if stretched
, spring pulls inward ,
if compressed ,
it pushes outward .
thus it is a restoring force
-
-
this force is given by Hookes law : Esp = -k*
K is it describes how stiff spring
spring constant ; is
-
-spring acts opposite to displacement causing force C-sign
Section 4 . 2
gravitational force Fg on object is its weight
mass (m) of object is the amount matter in object
.
the weight is
given by
Eg ma =
is still
g = -9 81 .
m/sy
we measure m in kg
the unit of force is the newton (N) ,
where N =
Kg m/s
.
mass is same wherever object is
weight depends on strength of gravity
.
, Section 43 .
We can write a force in component form :
F FxX = +
Fyy +
Fzz
the net force on an object is sum of all forces :
Fnet [F F F Fz=
=
,
+ + ...
Fne+ X = F
,x = F, x +
E2X
Fnety SFiy =
= F
, y
+
Ezy
if we have the components ,
then we can find magnitude & direction.
every force is exerted
by one object another object.
·
on
the net force object only includes forces on that object.
on
acting
·
We ignore any internal Forces , only considering external forces .
Free-Body Diagrams FBD
·
draw object of interest as a point .
We draw each force from object
acting Vector point away
·
on
object as a
ideally the of correspond to strengths of but don't need to be too concerned
, lengths arrows should forces ,
w/ this.
EX person
pushing box
.
across a frictionless surface
FN
A
· Ex or
↓
Eg
Section 4 4 .
Newtons First Law
A in motion atconstant
body at rest will remain at rest ,
and a
body in motion remains speed
in a like unless is acted upon by force .
straight ,
a external
so, no net force ,
no
change in t
only net force matters not individual forces
Cindividual forces balance
,
-
mathematically : V =
constant as long as Fnet =
Also called law of inertia
inertia describes of an to resist to its motion.
tendency object changes
·
Newtons Second Law Acceleration : of system directly proportional to the forces inversely proportional to the
mass .
Fret
=
Enet or
= m
