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BILKENT ERZURUM LABORATORY HIGH SCHOOL
CENTER OF MASS
LOGO
Cemre Çise KADIOĞLU 102
KEY WORDS
Center of gravity, plumb line
Weight, torque
Resultant-gravitional forces
Stability
Balance
Equilibrium
Turning effect
What is centre of mass?

Gravitional forces on
particles of stick
The small forces act like a single force at
G. This means that they have the
resultant force at G.
The resultant force is the stick’s weight.
G is the centre of mass.
What is centre of mass?
Centre of mass of a body is the body that
moves as though all of the mass were
applied there.
Finding centre of mass
 If the object is uniform, for example a meter
stick, the center of mass will be at the exact
geometric center.
G
Intersection pointCentre of mass
 But, if the shape is irregular we use plumb line.
 Draw lines from each vertex along the plumb
line by assuming that the point is on that line
 After drawing the lines the centre of the mass
will be on the intersection point of these lines.
Finding the centre of mass
 But, if the shape is irregular we use plumb line.
 Draw lines from each vertex along the plumb
line by assuming that the point is on that line
 After drawing the lines the centre of the mass
will be on the intersection point of these lines.
Plumb line
Intersection point-centre
of mass
Balancing unequal masses are again
about centre of mass
M2
For example,
M1
d2
d1
The bus is heavier than the car so they’re
not in balance.
In order to balance the system, we
should change their distances to the
support.
d1
m1.d1=m2.d2
Now they’re in balance.
d2
Stability –Equilibrium
If an object isn’t moving and remainig
same, the object is stable.
 State of rest or balance due to the equal
action of opposing forces is called
equilibrium.
When the object is stable it’s also in
equilibrium which means the forces
acting on the object and the forces
turning effects are in balance.
Stability-Equilibrium
Will turn to
its original
position
Small
force will
turn it over
Will definetely fall
over before another
force is applied
Types of equilibrium
There are three states of equilibrium,
Stable equilbrium
The objects that have wide base also
have the lower centre of mass.
The lower the centre of mass is, the
more stable object is.
So it’s more difficult to fall over an object
with wider base.
Unstable equilibrium
The objects that have very little base,
have high centre of mass.
And if these objects are tilted the centre
of mass immediately passes beyond the
base.
So they’re not stable and it’s easy to fall
these objects over.
Neutral equilibrium
The objects that are in neutral
equilibrium stay where they’re lefted.
When moved, it changes the position.
Wherever they stay, their center of mass
is always over their base.
References
Complete Physics for IGCSE
http://dev.physicslab.org/Document.asp
x?doctype=3&filename=RotaryMotion_Ce
nterMass.xml
http://dictionary.reference.com/browse/
equilibrium
http://en.wikipedia.org/wiki/Center_of_
mass
http://eteach.engr.wisc.edu/meibom/esp
p/slides/espp.ppt
http://solar.njit.edu/~cdenker/physics11
1_lecture08.ppt