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Earth and Space - The Water Cycle and Weather Patterns

Grade 5IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

The Water Cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth through various states of H2OH_2O.

Evaporation is the process where liquid water (H2O(l)H_2O_{(l)}) absorbs solar energy and transforms into water vapor (H2O(g)H_2O_{(g)}).

Transpiration is a biological process where plants release water vapor (H2O(g)H_2O_{(g)}) into the atmosphere through small pores in their leaves called stomata.

Condensation occurs when water vapor (H2O(g)H_2O_{(g)}) loses thermal energy and cools down to form liquid water droplets (H2O(l)H_2O_{(l)}), which cluster together to form clouds.

Precipitation is the product of condensation that falls under gravity, including rain, snow (H2O(s)H_2O_{(s)}), sleet, or hail.

Weather patterns are influenced by the interaction of solar radiation, the atmosphere, and the water cycle, measured by variables like temperature (TT), air pressure (PP), and humidity.

Air Pressure is the weight of the atmosphere pressing down on Earth. Changes in pressure often indicate changes in weather; for example, low pressure often brings clouds and precipitation.

Humidity is the amount of water vapor present in the air. Relative humidity is expressed as a percentage (%) of the maximum amount of moisture the air can hold at a specific temperature.

📐Formulae

H2O(l)+Heat EnergyH2O(g)H_2O_{(l)} + \text{Heat Energy} \rightarrow H_2O_{(g)}

H2O(g)Heat EnergyH2O(l)H_2O_{(g)} - \text{Heat Energy} \rightarrow H_2O_{(l)}

Relative Humidity=(Actual Water VaporMaximum Water Vapor Capacity)×100%\text{Relative Humidity} = \left( \frac{\text{Actual Water Vapor}}{\text{Maximum Water Vapor Capacity}} \right) \times 100\%

TCelsius=59(TFahrenheit32)T_{Celsius} = \frac{5}{9}(T_{Fahrenheit} - 32)

💡Examples

Problem 1:

During a sunny afternoon, the temperature is 30C30^{\circ}C. A puddle of water (H2O(l)H_2O_{(l)}) disappears after a few hours. What process occurred, and what happened to the energy?

Solution:

The process is evaporation.

Explanation:

The liquid water molecules (H2O(l)H_2O_{(l)}) absorbed thermal energy from the Sun, increasing their kinetic energy until they transitioned into a gaseous state (H2O(g)H_2O_{(g)}).

Problem 2:

A weather station records that the air contains 10g/m310g/m^3 of water vapor, but the air at that temperature can hold a maximum of 20g/m320g/m^3. Calculate the Relative Humidity.

Solution:

Relative Humidity=(1020)×100%=50%\text{Relative Humidity} = \left( \frac{10}{20} \right) \times 100\% = 50\%

Explanation:

Relative humidity is the ratio of current water vapor to the maximum possible water vapor the air can hold at that temperature, expressed as a percentage.

Problem 3:

Explain why dew forms on grass in the early morning when the temperature drops to 10C10^{\circ}C.

Solution:

This is caused by condensation.

Explanation:

As the temperature (TT) decreases at night, the air can hold less H2O(g)H_2O_{(g)}. When the air cools to its dew point, the water vapor loses energy and changes phase back into liquid droplets (H2O(l)H_2O_{(l)}) on cool surfaces.