Heat on Earth 8.10A RECOGNIZE THAT THE SUN PROVIDES THE ENERGY THAT DRIVES CONVECTION WITHIN THE ATMOSPHERE AND OCEANS, PRODUCING WINDS AND OCEAN CURRENTS [INCORPORATE 6.6B INTO CONVECTION]
A few reminders Density is a PHYSICAL PROPERTY of a substance that can be measured To calculate - Density is mass/volume The Sun provides most of the energy for our planet The additional source of heat is from the core
Convection Current Exploration:
Post-Demo Discussion: Hot air rises because it is less dense and then sinks as it cools. In the investigation, students observe hot water rising and then the cold water sinks. During these investigations students investigate how heat moves through water Convection currents are circular patterns that move air and liquids as a result of unequal heating and cooling. Hot air rises because it is less dense and then sinks as it cools. In the investigation, students observe hot water rising and then the cold water sinks. Where on earth do we observe convection currents?
Uneven heat from the Sun causes Earth is tilted at 23.5 degrees. The earth rotations and revolves around the Sun As we learned in a previous lesson, this means that the Earth receives different amounts of sun based on where you are on the planet as well as by the season
Recall: Direct light hitting the equator area, creates warm temperatures As you go away from the tropics, the sun s rays are more indirect. The light and heat is spread out, creating colder temperatures
The Sun heats the water and land Here we have a demo on heat, land and water. The lamp is acting as the Sun to heat each of the substances On your page, you have places to record information from this demo
Land/Water Heat Transfer Demo Key take aways : 1. One of the keys to understanding weather and climate is learning about the difference in the way that water and land heats up and cools off 2. The Sun s heat is absorbed at a different rate by different substances. 3. The air around these substances (land and water) through the transfer of heat energy, gains the heat. Once the temperature of the air begins to go up, the air mass itself rises because it s density has changed!
Why the difference? All 3 of these things: solid (land), liquid (water) and gas (air) have different densities and therefore hold and pass along heat differently!
Land and Water Heat the Air Around it: At the heart of it, we are talking about energy transformation Remember, energy transformation is he change of energy from one form to another The starting form of thermal (heat) energy for Earth, is radiation from the Sun. Once it reaches Earth, it is transferred by either conduction or convection from substance to substance. When the air gets heated, it behaves differently because it s properties change (density specifically)
The Property of Density The more dense an object is, the more tightly packed the atoms are. Less dense objects have fewer molecules in the same amount of space.
Can density change? Yes! As things such as air heat up (the temperature increases), the molecules start to move and need more space. This movement of the molecules increases the volume and therefore less matter is contained in the same space. This is why hot air rises!
Critical Thinking Look at the image. What is it demonstrating? Does this show that air has weight? Yes! Density and weight are closely correlated, air has mass, which also means it has weight.
What is air or atmospheric pressure? The air around you has weight, and it presses against everything it touches. That pressure is called barometric pressure, or air pressure. It is the force exerted on a surface by the air above it as gravity pulls it to Earth. pressure = force/area
Temperature differences cause pressure differences Air temperature is generally higher at ground level due to heating by the Sun of the land It generally decreases with increasing altitude. In cold air, the molecules are more closely packed together than in warm air, so cold air is more dense than warm air. The more density a mass of air has, the higher the pressure.
High pressure moves to low pressure However, air lower in the atmosphere (closer to Earth) is more dense than air above, so air pressure down low is greater than air pressure higher up. Since warm air is less dense and creates less air pressure, it will rise; cold air is denser and creates greater air pressure, and so it will sink.
High pressure moves to low pressure When warm air rises, cooler air will often move in to replace it, so wind often moves from areas where it's colder to areas where it's warmer. The greater the difference between the high and low pressure or the shorter the distance between the high and low pressure areas, the faster the wind will blow.
Convection currents are caused by changes in density The atmosphere experiences convection currents due to temperature differences (density differences) Instead of one or two large convection currents around the globe, there are smaller convection cells.