Transcript Force Diagrams #1-3 (print version)

Force Diagrams (Free Body Diagrams)
Example 1
Consider the box pulled by a string
that remains at rest.

FN

F fsf
Box


Fg

FT
String
Since the box has four
interactions it has four forces
acting upon it.
Table
Earth
Force Diagrams (Free Body Diagrams)

FN
Example 1
Consider the box pulled by a string
that remains at rest.


F fs

FT


FTx

Fg

FTy

Since v  constant
Fg  FN  FTy
F fs  FTx

Since v  constant
Force Diagrams (Free Body Diagrams)
Example 2
Consider the box on a frictionless
incline.

FN
Incline
Box


Fg
Earth
Since the box has two
interactions it has two forces
acting upon it.
Force Diagrams (Free Body Diagrams)
Example 2
Consider the box on a frictionless
incline.
y
x

 Rotate the x-axis parallel to the motion so that the motion is one dimensional!
Force Diagrams (Free Body Diagrams)
Example 2
Consider the box on a frictionless
incline.
y


Fgy

Fgx

Fg
x
 Rotate the x-axis parallel to the motion so that the motion is one dimensional!
Force Diagrams (Free Body Diagrams)
Example 2
Consider the box on a frictionless
incline.
y
y


F
x gy

Fgx
x


Fg
 Draw the y-component of the force of gravity first so that the angle of inclination
is the included angle!
Force Diagrams (Free Body Diagrams)
Example 2
Consider the box on a frictionless
incline.
Are the forces balanced?
y

FN
FN  Fgy

Since v  constant


Fgy

Fgx


Fg
x
Force Diagrams (Free Body Diagrams)
Example 2
Consider the box on a frictionless
incline.
The box speeds up as it moves down the incline

because of the net force provided by Fgx .
y

FN
FN  Fgy

Since v  constant


Fgy

Fgx


Fg
x
Force Diagrams (Free Body Diagrams)
Example 3
Consider the box sliding down the
incline at a constant velocity.

FN

F fkf
Box

Incline

Fg
Earth
Since the box has three
interactions it has three
forces acting upon it.
Force Diagrams (Free Body Diagrams)
Example 3
Consider the box sliding down the
incline at a constant velocity.
y
x

 Rotate the x-axis parallel to the motion so that the motion is one dimensional!
Force Diagrams (Free Body Diagrams)

Since v  constant
Example 3
Consider the box sliding down the
incline at a constant velocity.
y
FN  Fgy
F fk  Fgx

FN

Since v  constant
x

F fk


Fg


Fgy

Fgx
 Draw the y-component of the force of gravity first so that the angle of inclination
is the included angle!