6th grade
What causes rivers to flow? Gravity pulls water downhill.
What is a watershed? An area of land that drains water into a river system.
What is a divide? A ridge that separates one watershed from another.
How do ponds and lakes form? Water collects in hollows and low-lying areas of land.
What is groundwater? Water stored in cracks and spaces in soil and rock.
What is an aquifer? A body of saturated rock or sediment that holds and allows water to flow.
How can people reach groundwater? By digging or drilling a well.
What is the hydrosphere? All the water on Earth, including liquid water, ice, and water vapor.
What is the water cycle? The continuous movement of water from Earth's surface to the atmosphere and back.
What is evaporation? The process in which liquid water changes into water vapor.
What is transpiration? The process in which plants release water vapor through their leaves.
What is condensation? The process in which water vapor cools and changes into liquid water.
What is precipitation? Water that falls from clouds as rain, snow, sleet, or hail.
What percentage of Earth's water is fresh water? About 3 percent.
Where is most of Earth's fresh water stored? In glaciers and ice caps, with much of the rest underground.
Where is most of Earth's salt water found? In oceans and seas.
What is the atmosphere? The envelope of gases surrounding Earth.
How does the atmosphere protect life? It helps block harmful solar radiation, regulates temperature, and provides gases needed for life.
Where is most atmospheric gas found? Close to Earth's surface.
What is the most abundant gas in Earth's atmosphere? Nitrogen, about 78 percent.
What percentage of the atmosphere is oxygen? About 21 percent.
What makes up the remaining roughly 1 percent of dry air? Argon, carbon dioxide, and other trace gases.
What is air? A mixture of gases in Earth's atmosphere.
Does gas take up space? Yes, gases occupy volume.
Does gas have mass? Yes, gas is matter and has mass.
How can you demonstrate that gas has mass? Compare the weight of a suitable balloon before and after inflating it.
What is air pressure? The force exerted by air molecules on a surface per unit area.
What causes air pressure? Air molecules collide with surfaces, and gravity helps keep the atmosphere near Earth.
What is altitude? Height above sea level.
What happens to air pressure as altitude increases? Air pressure decreases.
Why does air pressure decrease at higher altitudes? There is less air above you pushing down.
What instrument measures air pressure? A barometer.
How does warm air compare with cold air? Warm air is generally less dense than cold air at the same pressure.
What is density? The amount of mass in a given volume.
What are the four main atmospheric layers from lowest to highest? Troposphere, stratosphere, mesosphere, thermosphere.
Which atmospheric layer do we live in? The troposphere.
Where does most weather occur? In the troposphere.
Which layer contains the ozone layer? The stratosphere.
What does the ozone layer do? It absorbs much of the Sun's harmful ultraviolet radiation.
In which layer do most meteors burn up? The mesosphere.
Which is the outermost of the four main layers? The thermosphere.
Where do auroras occur? Mainly in the thermosphere, in the ionosphere region.
What is the main source of energy driving Earth's systems? The Sun.
What are the three main methods of heat transfer? Conduction, convection, and radiation.
What is conduction? Heat transfer through direct contact.
What is convection? Heat transfer by the movement of fluids, such as air and water.
What is radiation? Energy transfer by electromagnetic waves; it does not require direct contact or a medium.
How does the Sun heat Earth? Through radiation.
How does the ground warm nearby air? Heat transfers from the warm ground to air touching it by conduction.
How does convection move heat in the atmosphere? Warm, less-dense air rises and cooler, denser air sinks.
What is wind? Air moving parallel to Earth's surface.
Why does wind form? Unequal heating creates air-pressure differences that cause air to move.
How does air generally move in relation to pressure? From areas of higher pressure toward areas of lower pressure.
What happens to warm air? It expands, becomes less dense, and tends to rise.
What happens to cool air? It is generally denser and tends to sink.
What is a sea breeze? A local wind that blows from the sea toward the land during the day.
Why does a sea breeze form during the day? Land heats faster than water, warm air rises over land, and cooler air from over the water moves inland.
How do land and ocean temperatures compare during a daytime sea breeze? The land is usually warmer than the ocean.
How do air pressures compare during a daytime sea breeze? Pressure near the surface is generally higher over the cooler water than over the warmer land.
What are global winds? Winds that move air over large areas of Earth.
Why are global winds driven by unequal heating? The equator receives more direct solar energy than the poles, creating temperature and pressure differences.