Moment of a Force - I Love Physics Forever!
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Transcript Moment of a Force - I Love Physics Forever!
Moment of a Force
Learning Objectives
recall and use the relationship
between the moment of a force and
its distance from the pivot:
Moment = force x perpendicular
distance form pivot
recall that the weight of a body acts
through the centre gravity
Define the torque of a couple
Moments
Forces can make
objects turn if there is
a pivot.
The see-saw
In order to make the seesaw turn
about its pivot, forces have to be
applied on either side of the plank
The see-saw
What happens when
one person moves
closer to the fulcrum
or pivot?
The turning effect of
the force is also
dependent on the
distance of the force
from the pivot.
Turning effect
the turning effect is
called the moment
of force (or simply
"moment“)
the distance is
called the moment
arm (or lever arm)
of the force.
Moment of a Force
To work out a
moment, we need to
know two things:
the force or weight
applied
the distance from the
pivot that the force or
weight is applied.
Force and distance
must be
perpendicular to each
other
Moment of a Force
Product of force and the
perpendicular distance
From the pivot
Moment and Equilibrium
Conditions for Equilibrium
Net force is zero
Net moment is zero at any point
Example
Find the force F that will balance the
seesaw.
Example
Find the force F that will balance the
seesaw.
Center of gravity
The centre of gravity of an object is
the point where the whole weight of
the object may be considered to act.
Center of gravity
For a regularlyshaped object, the
centre of gravity is
at its centre and,
where supported
there, it balances.
Example
A uniform plank, 100 cm long and weighing
1.0 N is balanced at its midpoint by a
support. A weight of 1.20 N is hanged 5 cm
from the left end. It was found out that an
unknown weight W would balance the plank
if it is positioned 72 cm from the left end.
What is the weight W of the object?
How much force is exerted by the support on
the plank?
Couple
Two parallel forces
equal in magnitude
But opposite in
direction
Has a turning
effect about a pivot
located midway
between them
Torque of a Couple
Product of
One of the forces
And the distance between them
Your turn!
Answer numbers 1 to 4, page 56