Biomedical Engineering Reference
In-Depth Information
8.3.1 Objectives
• To calibrate a spring scale made with a rubber band
• To determine the weight of objects and the magnitude of forces present in an
experimental system
• To establish the conditions of static equilibrium relative to translation
8.3.1.1 Necessary Materials
- Rubber band
- Paper clips
- Objects with known mass
- 30 cm ruler or a tape measure
- Protractor
The objects of known mass can be a 1.0 or 2.0 l plastic bottle with a known quantity
of water. Remember that the mass of water corresponding to a volume of 1.0 l is
1.0 kg
1
and, hence, represents a weight of 10 N. If it is not possible to determine the
volume of water in known units, work with an arbitrary unit of mass, a.u.m.,
adopting a certain volume of water such as a glass of water or a soda can as a
standard.
8.3.2 Activity 1: Construction and Calibration of a Spring
Scale (Dynamometer)
The word dynamometer originates from the Greek dynamis. It is an apparatus
developed to measure the magnitude of a force. A rubber band or a spring can be
used to construct a spring scale. In the case of a spring, we can apply Hooke's law
that states: the change in the length,
x
, observed in a spring is directly proportional
to the magnitude of the force,
F
, applied to it, that is, if we double the magnitude of
the force, the change in the length of the spring is doubled and so on. This
proportionality can be expressed by (
8.1
):
Δ
F
¼
k
x
,
Δ
(8.1)
1
1.0 l of water
1,000 cm
3
. Considering the density of water
1.0 g/cm
3
, we obtain for the mass
¼
¼
of water
¼
1,000 g
¼
1.0 kg.
