Transcript Create a FBD that represents the situation below

Create a FBD that represents the
situation below
2 ropes are holding the
object up and the
object is motionless
Ft2 (R, B)
Ft1 (R, B)
Fg (E, B)
But this is different than any of the
other problems we have done
because for the first time, we’ve
encountered a scenario where it’s
not completely obvious to the eye
exactly how the forces balance
Should the forces be balanced?
• Yes, because the object is motionless (constant
velocity)
• Therefore, net force = 0
Balanced
(obvious to
the eye)
Balanced
(not so
obvious to
the eye)
=
+
2-D force vector
(up & to the right)
Component vectors
2 horizontal component
vectors cancel
(balanced)
2 vertical
component vectors
cancel downward
vector (balanced)
Any vector directed in 2
dimensions can be thought
of as having an influence in
2 different directions
• Made up of 2 parts
Each part of a 2-D vector is
known as a component
vector
• The combined influence
of the 2 components is
equal to the influence
of the single 2-D vector
• Therefore, we can
replace the 2-D vector
with the component
vectors
Much more obvious to
the eye how the forces
balance
Now try to create the FBD of this
situation
Object is motionless on an incline
We know that the force should balance since the
object is motionless (constant velocity)
• Net force = 0
FN (R, B)
Ff (R, B)
FN (R, B)
Remember, normal
force is
perpendicular to
surface
Remember,
friction force
is parallel to
surface
Ff (R, B)
Fg perp.
Fg (E, B)
Fg parallel
Fg (E, B)
We know that the forces must
be unbalanced because the
problem does not state that
the object is going at a
constant velocity
• We know from past
experience that objects
going down ramp
accelerate
• Net force not equal to 0
Object slides without friction
FN (T, B)
F net = 0
Fg
Fg
Fg
Fg (E, B)
By displaying this, we are 100% sure
the force that is responsible for this
accelerated motion and in what
direction
• VERY IMPORTANT FOR OUR
UNDERSTANDING OF MOTION!