Page 208 - Physics

Physics for Secondary Schools
Concept of energy
Energy plays a role in our
daily activities, such as
cooking, freezing, lighting, and
manufacturing. In science and
engineering, energy is defi ned
as the ability to perform work.
An object possessing energy can
do work and transfer that energy
to another object, enabling it
to perform work as well. In
essence, energy quantifi es an
object's capacity to do work.
Thus, energy is referred as the
ability to do work.
To understand the concept of
energy, imagine a person driving
a nail into wood, as shown in
Figure 9.4. When the hammer is
lifted, it gains energy. When the
raised hammer strikes the nail,
the energy from the hammer is
transferred to the nail, driving it
into the wood.
Figure 9.4: Driving a nail
into wood
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Physics Form 1 Final.indd 202
Since work is done when energy is available,
the SI unit of energy is the same as that of
work, that is, joule (J). One joule of energy is
the energy required to do one joule of work.
Sometimes energy is expressed using a larger
unit of energy called kilojoule (kJ) such that
1 kJ equals to 1000 J.
Forms of energy
Energy exists in different forms, including
mechanical energy, chemical energy, electrical
energy, heat energy, light energy, sound energy
and nuclear energy. One form of energy can be
converted into another form, as illustrated in
Figure 9.5.
Figure 9.5: Forms of energy
Mechanical energy is the energy possessed by an
object due to its position or motion. The mechanical
energy due to the position of the object is referred
to as the potential energy (PE). Meanwhile, the
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