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Ripples In
Water
What Causes Ripples In Water?
John Staughton
Ripples in
water are more formally known as capillary waves, and are caused by the subtle
interaction of wind and water, or the physical interaction of the water with
another object.
Have you ever stood at the edge of
a lake on a hot summer day and stared out across the water?
Even if there isn’t a whisper of
wind against your face, you will likely still see faint lines and
irregularities in the water.
The light will reflect off movement
at the surface, and small ripples will be seen in patches, sometimes appearing
to move in different directions.
Imagine picking up a stone and
chucking it into the lake, where it lands with a satisfying splash, and an
expanding ring of ripples will appear.
These patterns and shapes that we
see or create in water bodies are commonly referred to as ripples, but why do
they form and what affects how long they last?
What is a Ripple?
Even on a day when you don’t feel
any wind, there will always be some movement in the air, and at the surface of
a water body, that movement causes small ripples to form.
Wind energy is being transferred to
the minuscule water molecules, which begin to move up and down, gently rising
and falling, pulling along with the molecules beside them.
However, the surface tension of
water is quite strong, due to the polar nature of water molecules, and this
tension will stop the ripples from perpetuating very far or for very long.
The energy transferred into the
water is quickly used up in moving those molecules up and down, so the ripples
fade.
This is what gives the ripples on a
lake their transient, sparkling appearance, as they briefly rise and catch the
light before settling back into stillness.
When you throw a rock into a body
of water, the rock will push water out of its way as it enters, causing ripples
to move away from its point of entry in a circle or ring shape.
Water will then rush back in to
fill the empty space, which can often cause a splash, resulting in more ripples
forming.
You can try this yourself by
dropping a marble straight down into a bowl of water. Watch the resultant
splash rise straight up and then fall back in, sending out a second ring of
ripples.
The larger the rock, the greater
the effect and the stronger the ripple, meaning that it will last longer before
disappearing.
The reason that these ripples don’t
behave like waves on a beach is because they aren’t strong enough; they lack
the energy to persist in the face of water’s strong surface tension.
These types of ripples may also
form when water is moving in a certain direction and encounters an obstacle,
such as a fishing boat, a breakwall, or even your feet as they dangle off a
dock!
Water molecules will encounter an
object and move upwards against it, before being pulled back down by the
neighboring molecules.
This interaction causes a ripple to
form that moves in the opposite direction of the water’s initial motion.
Now, while a ripple is a type of
wave motion — a capillary wave, to be precise — when we are talking about water
bodies, there is a clear difference between a ripple and a wave.
Ripples vs Waves vs Swells
As mentioned above, a ripple is a
transient, short-lived phenomena that quickly disappears once its input energy
is used up.
However, if wind continually moves
over a body of water, creating a steady stream of ripples, they can begin to
accrue more energy, and will turn into waves, like those you might see crashing
on a beach.
While ripples are unable to overcome
the force of surface tension, waves can build up enough energy to do so if the
wind blows steadily over a large enough patch of water.
Such waves will always flow in the
same direction as the wind, and will shift direction if the wind changes.
When waves move into shallower
water, the bottom part of the wave will decrease in speed, and the top part of
the wave will overtake it, causing the wave to break.
This can also be seen in the ocean
open, particularly during a storm or when the seas are choppy, i.e., when
different weather systems are interacting, or when the wind is rapidly changing
direction.
If the wind is persistent and
strong, it can begin to generate the most persistent type of movement — a
swell.
While waves always move in the same
direction as the wind, a swell forms when those waves move out of the area they
were initially made.
The water of a swell has gathered
enough energy and momentum that it can actually move against the wind,
sometimes traveling vast distances, across entire oceans, without losing its
energy.
A swell is typically difficult to
see against the horizon, as it is often longer, more even and slower-moving
than normal waves.
Also, the distance between the
troughs and peaks of a swell is usually much greater than that distance in
waves formed by the wind.
A Final Word
Clearly, water is able to store and
harness a lot of wind energy under the right conditions, but ripples are simply
too transient, too small and have too little energy to persist and travel for
long distances.
However, if you get a large enough
rock and drop it from a high enough height, you may be able to create a ripple
that travels out from the middle of the lake to the shoreline!
John Staughton is a traveling writer, editor, publisher and
photographer who earned his English and Integrative Biology degrees from the
University of Illinois. He is the co-founder of a literary journal, Sheriff
Nottingham, and the Content Director for Stain’d Arts, an arts nonprofit based
in Denver. On a perpetual journey towards the idea of home, he uses words to
educate, inspire, uplift and evolve.
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