# Currents, Waves, And Tides

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Test over currents, waves, and tides aimed at sixth grade earth science students.

• 1.

### The wind blows on the water, passing it's energy to the water. As this energy passes through the water, in what way do the water molecules move?

• A.

In waves towards the shore

• B.

In a small vertical circle

• C.

In the direction of the waves

• D.

Against the currents

B. In a small vertical circle
Explanation
When the wind blows on the water, it transfers its energy to the water molecules. This energy causes the water molecules to move in a small vertical circle. The circular motion is a result of the wind's energy causing the water molecules to oscillate up and down, creating waves. Therefore, the correct answer is "in a small vertical circle."

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• 2.

### The lowest point of a wave is the:

• A.

Crest

• B.

Wavelength

• C.

Trough

• D.

Frequency

C. Trough
Explanation
The lowest point of a wave is called the trough. In a wave, the trough is the point where the displacement or amplitude is at its lowest. It is the opposite of the crest, which is the highest point of the wave. The wavelength refers to the distance between two consecutive troughs or crests in a wave. Frequency, on the other hand, represents the number of complete waves passing a certain point in a given time.

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• 3.

### The highest point of a wave is:

• A.

Crest

• B.

Wavelength

• C.

Trough

• D.

Frequency

A. Crest
Explanation
The highest point of a wave is called the crest. In a wave, the crest refers to the point where the displacement of the medium is at its maximum positive value. It is the peak of the wave, located above the equilibrium position. The crest is followed by the trough, which is the lowest point of the wave.

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• 4.

### When the wind blows across a body of water (like the ocean), ________________ between the water and air causes the water to move.

• A.

Ions

• B.

Gravity

• C.

Friction

• D.

Density

C. Friction
Explanation
When the wind blows across a body of water, the friction between the water and air causes the water to move. Friction is the force that opposes the motion of two surfaces in contact with each other. In this case, as the wind pushes against the surface of the water, the friction between the air and water molecules causes the water to be dragged along in the direction of the wind. This movement of water is what we observe as waves or currents.

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• 5.

### The size of a wave is NOT affected by the:

• A.

Length and time the wind blows across the water

• B.

Salinity of the water

• C.

Strength of the wind (how hard the wind is blowing)

• D.

Distance the wind blows across the water

B. Salinity of the water
Explanation
The size of a wave is not affected by the salinity of the water. The size of a wave is primarily determined by the length and time the wind blows across the water, the strength of the wind, and the distance the wind blows across the water. Salinity refers to the amount of salt in the water and does not directly impact the size of the waves.

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• 6.

### This occurs when circulation in the ocean brings deep, cold water to the ocean surface:

• A.

Rotation of the earth

• B.

Density

• C.

Coriolis effect

• D.

Upwelling

D. Upwelling
Explanation
Upwelling refers to the process in which deep, cold water from the ocean is brought to the surface. This phenomenon occurs due to various factors such as wind patterns, ocean currents, and the rotation of the earth. As the wind blows parallel to the coastline, it pushes the surface water away, causing an upward movement of the colder, nutrient-rich water from below. This upwelling of deep water is essential for marine ecosystems as it brings nutrients to the surface, supporting the growth of phytoplankton and subsequently, the entire food chain.

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• 7.

### ______________ water rises and ________________ water sinks

• A.

Warm, cold

• B.

Cold, warm

• C.

None of the above

• D.

All of the above

A. Warm, cold
Explanation
Warm water rises and cold water sinks due to differences in density. When water is heated, its molecules become more energetic and spread out, causing the water to expand and become less dense. This less dense warm water rises to the surface. On the other hand, cold water is denser because its molecules are closer together. Therefore, it sinks to the bottom. This process is known as convection and plays a crucial role in ocean currents and weather patterns.

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• 8.

### The amount of salt in a given amount of water is:

• A.

Coriolis effect

• B.

Salinity

• C.

Density current

• D.

Surface current

B. Salinity
Explanation
Salinity refers to the concentration of dissolved salts in a given amount of water. It is typically measured in parts per thousand (ppt) or percentage. Salinity can vary depending on factors such as evaporation, precipitation, and the presence of freshwater inputs. It is an important parameter in oceanography and is used to understand the composition and properties of seawater. The correct answer, salinity, accurately describes the amount of salt present in a given amount of water.

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• 9.

### What causes the currents to curve instead of moving in straight lines?

• A.

The moon's gravity

• B.

Wave height

• C.

Coriolis effect

• D.

Density currents

C. Coriolis effect
Explanation
The Coriolis effect is responsible for causing currents to curve instead of moving in straight lines. This effect is a result of the Earth's rotation and the conservation of angular momentum. As the Earth rotates, it causes moving objects, such as ocean currents, to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection is what causes the currents to curve and follow a circular path rather than moving in a straight line.

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• 10.

### What is the main cause of the gulf steam?

• A.

Storms

• B.

Winds that blow now and then

• C.

Winds that blow in regular directions all the time

• D.

The moon's gravity

C. Winds that blow in regular directions all the time
Explanation
The main cause of the Gulf Stream is the winds that blow in regular directions all the time. These winds, known as the Trade Winds, blow from east to west in the tropics and from west to east in the mid-latitudes. As these winds blow across the surface of the ocean, they create a surface current that moves warm water from the tropics towards the North Atlantic. This warm water is what forms the Gulf Stream, a powerful ocean current that influences the climate of the eastern coast of North America and Europe. The consistent and persistent nature of these winds is what drives the continuous flow of the Gulf Stream.

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• 11.

### Density currents are caused by:

• A.

Differences in temperature

• B.

Differences in salinity

• C.

The moon's gravity

• D.

A and B are both correct

D. A and B are both correct
Explanation
Density currents are caused by differences in temperature and differences in salinity. When there are variations in temperature or salinity within a fluid, it leads to differences in density. This density difference causes the fluid to flow in a current, with denser fluid sinking and less dense fluid rising. These currents can occur in both the ocean and the atmosphere and play a crucial role in the distribution of heat and nutrients, as well as the circulation of water and air masses. Therefore, both temperature and salinity differentials contribute to the formation of density currents.

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• 12.

### What type of ocean motion is influenced by the moon and the sun?

• A.

Density currents

• B.

Surface currents

• C.

Waves

• D.

Tides

D. Tides
Explanation
Tides are the type of ocean motion that is influenced by the moon and the sun. The gravitational pull of the moon and the sun causes the ocean waters to rise and fall in a rhythmic pattern, creating tides. This gravitational force is strongest when the moon and sun are aligned, causing higher high tides (spring tides) and lower low tides. When the moon and sun are at right angles, the gravitational force is weaker, resulting in lower high tides (neap tides) and higher low tides. Tides play a crucial role in various coastal processes and ecosystems.

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• 13.

### Surface currents are caused by

• A.

Wind that blows every now and then

• B.

Wind that blows in regular directions

• C.

The moon's gravitational pull

• D.

Differences in salinity and temperature

B. Wind that blows in regular directions
Explanation
Surface currents are caused by wind that blows in regular directions. This is because wind patterns are influenced by the Earth's rotation and atmospheric pressure systems. The prevailing winds, such as the trade winds and the westerlies, consistently blow in specific directions. These winds push the surface waters of the ocean, creating currents that flow in a predictable manner. The regularity of the wind direction ensures the continuity and stability of these surface currents.

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• 14.

### When the sun, moon, and earth are all aligned (in a straight line), you have a

• A.

Density current

• B.

Neap tide

• C.

Surface current

• D.

Spring tide

D. Spring tide
Explanation
A spring tide occurs when the sun, moon, and earth are all aligned in a straight line. This alignment creates a stronger gravitational pull, causing higher high tides and lower low tides. Spring tides happen during the new moon and full moon phases. The term "spring" in spring tide does not refer to the season, but rather to the concept of the tide "springing forth" or being particularly strong.

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• 15.

### The sun's rays are strongest at the____________ and weakest at the _______________:Hint: the stronger the rays, the hotter it gets!!!

• A.

Equator, poles

• B.

Poles, equator

• C.

Ocean floor, ocean surface

• D.

Midocean ridge, continental shelf

A. Equator, poles
Explanation
The sun's rays are strongest at the equator because this is the region that receives the most direct sunlight throughout the year. The equator is located near the middle of the Earth, where the sun's rays hit the surface at a more direct angle. This concentrated energy leads to higher temperatures and makes the equator hotter than other regions. On the other hand, the sun's rays are weakest at the poles because they hit the surface at a slanted angle, spreading out over a larger area. This results in less concentrated energy and lower temperatures at the poles.

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