Download Getting to Know: Energy Transfer and the Water Cycle

Getting to Know: Energy Transfer and the Water Cycle
Have you ever been to the beach on a hot day? If you have, you probably noticed that the wind coming off the water felt nice and cool, making you feel comfortable despite the oppressive summer heat. The reason that the waterfront is such a nice place to be in summer is that energy from the Sun does not warm the water as quickly as it does the land. The ocean is therefore much cooler than the nearby land and does not heat the air above it as much. Cooler air from over the ocean then rushes in to push out the warmer air above the land. The result is the wonderful ocean breezes that you can feel on your skin, even on the hottest of days!
Sea breezes result from the uneven
heating of Earth’s surface by the Sun.
How does energy from the Sun affect weather patterns on Earth?
Energy transfer in weather occurs on a global scale, and energy from the Sun has a huge
impact on water and wind currents on Earth. One way that the Sun affects weather is wind
patterns. The light from the Sun warms the ground, which in turn heats the air above it.
However, not all of the Earth’s surfaces absorb or radiate heat energy at the same rate. Land
heats up and cools down more quickly than water does. That is why the sand is hot at the
beach even when the water is cool. These temperature differences also affect the temperature
of the air, causing weather patterns such as sea breezes.
Warm air rises and expands and is said to have low pressure because it is less dense than
cooler air. Cooler air has high pressure because it is denser than warm air. The pressure
difference between the two kinds of air results in movement of air from high-pressure areas
to low-pressure areas. This movement is what we know as wind. The uneven heating of Earth
by the Sun is therefore responsible for wind patterns, which in turn have a direct impact
on weather.
Misconception 1: Is air weightless?
Air is not weightless—it has mass, just like any other kind of matter. Air is very light,
because it is composed of relatively light particles that are spread out very far from one
another.
Concept: Energy Transfer and the Water Cycle
Getting to Know
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What is the water cycle?
The Sun’s energy also affects the movement of water on Earth. This process is known as the water cycle, which is composed of three main phases: evaporation, condensation, and precipitation. The water cycle is a critical element in weather patterns.
The Sun’s heat causes water on Earth’s surface to change from a liquid to a gas form. The
evaporated water then rises into the air. The higher the air mass gets, the cooler the air
temperature becomes. Eventually, the water vapor begins to condense into tiny droplets that
form clouds in the sky. When the liquid droplets become heavy enough, they fall back to
Earth in the form of precipitation such as rain or snow.
Misconception 2: Does liquid water disappear when it evaporates?
Liquid water changes to invisible vapor in the air. However, it retains its chemical
makeup and does not cease to exist. Water is continually cycling through different Earth
systems and can change states between solid, liquid, and gas.
How do we measure the water in the air?
We measure the water that is in the air in a couple different ways. Humidity, for example, is
a measure of the percentage of moisture that is in the air. On humid days, the air feels very
moist and damp; while on days with low humidity, the air will feel very dry. Humidity varies
throughout the year, and is different from place to place.
Another measure of water in the air is known as dew point. This is the exact point at which the temperature and humidity in the air combine to cause moisture to condense and collect on a surface. This is, incidentally, where dew comes from. When the air reaches the dew point during the cooler periods that occur at night, water vapor collects on surfaces such as grass and leaves. This forms the dew that you can see early in the morning! The movement of energy through the water
cycle can be interesting and complex. In this
lesson, you will get to learn more about how this
constant energy transfer works and how it affects
other processes on Earth.
The dew point is the point at which
the temperature and humidity of the air
combine to cause moisture that collects
on a surface.
Misconception 3: Sometimes when I am drinking a glass of cold water, I can see
moisture forming on the outside of the glass. Does this moisture somehow come
from the liquid inside the glass?
The moisture on the outside of the glass actually comes from water vapor in the air. The
colder temperature of the glass causes the water vapor in the air just outside the glass to
condense into liquid form.
Concept: Energy Transfer and the Water Cycle
Getting to Know
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© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.