3B Scientific Stability Apparatus - Manual

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K
G
S
F
l
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Instruction sheet
3B SCIENTIFIC® PHYSICS
U15033 Stability apparatus with integrated plumb
6/03 ALF
®
The stability apparatus is used to demonstrate the sta-
bility of an object depending on the position of its center
of gravity above the supporting surface.
1. Description, technical data
The stability apparatus consists of 3 steel plates con-
nected by hinges to a frame made up of four steel rods
so that the vertical separation between the plates is equal.
A plumb line hangs suspended from the center of grav-
ity of the apparatus at the mid-point of the middle plate.
Dimensions: 180 mm x 150 mm x 290 mm
2. Principle
For a standing object the centre of gravity is only stable if
the plumb line is directly above the centre-point of the
surface at the base of the object. The force of gravity acts
effectively through the centre of gravity of the object
and is equally matched by the reaction of the surface. If
the plumb line is not above the centre of the base, the
force of gravity through the centre of gravity of the ob-
ject produces a moment which makes the object tend to
tip over.
At the center of gravity S there are two forces being ex-
erted, gravity G and the lateral force F, which tends to tilt
the body over the edge K. It causes a moment M
tilt
= Fh
about an axis formed by K. This moment is counteracted
by the moment due to the gravity M
gravity
= Gl. As long as
Fh = Gl, the object remains in equilibrium and does not
tip over. The force F = Gh/l serves as a measure for the
stability of an object resting on a surface. The greater the
gravity G, the lower the height h of the center of gravity
above the supporting surface and the greater the dis-
tance l from the edge K to the point at which the plumb
line would cross the surface, the more stable the object
will be.
3. Operation
• The stability apparatus is placed on a horizontal sup-
porting surface.
• The device is then tilted at various angles.
• Equilibrium is stable if the center of gravity is located
above the support base.
• Equilibrium is unstable if the center of gravity is lo-
cated directly above the edge that forms the axis of
rotation. (a slight push is enough to tip the apparatus
over.)
• If the center of gravity is no longer located over the
support base or over the tipping edge, the stability
apparatus tips over of its own accord.
• The position of the center of gravity can always be
surmised by the line of the plumb bob.
• To determine the force required to tip the apparatus
over, attach a 10 N dynamometer into the eyelet on
the side of the apparatus.
3B Scientific GmbH • Rudorffweg 8 • 21031 Hamburg • Germany • www.3bscientific.com • Technical alterations are possible
1 Steel plate
2 Plumb line
3 Steel rod
4 Hinge
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