Video Transcript
Which of the following is the term
used to refer to the energy that a moving object has due to its mass and its
velocity? A) Internal energy, B) Kinetic
energy, C) Mechanical energy, D) Potential energy.
Okay, so in this question, we are
considering an object that is moving and we’re trying to figure out which one of
these four is the term that refers to its energy due to its mass and velocity. Now, the first option is internal
energy. Well, when we say internal energy,
we should immediately think of a system of particles. So, for example, if we have a box
with lots of particles of gas inside this box, then the internal energy of this
system of particles is the total energy contained within this system.
In other words, the kinetic energy,
the motion energy due to these particles moving around inside the box, all at
different velocities and in different directions. And additionally, the potential
energy between these particles, as a result of their positions in space relative to
each other. But in simpler terms, it’s the
total energy contained within this system. And so, it’s not simply the energy
due to the mass and velocity of a moving object. Hence, this is not the answer we’re
looking for.
Option B, then, is kinetic
energy. Well, kinetic energy is indeed
movement energy. It is the energy that an object has
because of its mass and its velocity. And, we can see this by recalling
that the kinetic energy of an object, KE, can be found by multiplying half by the
mass, 𝑚, of the object by the velocity, 𝑣, of the object squared. And hence, the kinetic energy of an
object is dependent on the mass and the velocity of the object. So, it looks like option B is the
answer that we’re looking for.
Quickly looking at the remaining
options though, we can see that option C is mechanical energy, which is actually
defined as the sum of a system’s kinetic energy and potential energy. Well this time, the system that
we’re talking about doesn’t have to be a system of particles. It could be a macroscopic or
large-scale system. But the point is that this is not
the energy that our moving object has by virtue of its mass and its velocity. And hence, option C can be crossed
out as well.
And finally, option D is potential
energy. Now, potential energy is the energy
between objects due to their relative positions to each other. One good example of this is if we
have the Earth and if we’ve got an object, for example, a tennis ball suspended
above the Earth. Then, this tennis ball has some
gravitational potential energy at this distance from the Earth’s surface, by virtue
of the fact that the Earth has a gravitational field pulling all objects with mass
towards itself.
And so, because this tennis ball is
in the Earth’s gravitational field, it has some gravitational potential energy. But once again, this is potential
energy due to the tennis ball’s position relative to the Earth, more specifically
the height above the surface of the Earth, and therefore not due to its
velocity. Once again, the position is
important, not the speed at which the object is moving. And hence, we can cross out option
D as well. At which point, we’ve found the
answer to our question. The term used to refer to the
energy that a moving object has due to its mass and its velocity is kinetic
energy.
