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Preview of Period 13: The Energy Balance of the Earth 13.1 Sensitive and Non-Sensitive Systems What laws determine the motion of objects? Why can we predict the motion of some objects, but not others? 13.2 Probability and Sensitive Systems How is the sensitivity of a system related to the probability of a particular outcome? 13.3 Unpredictability in Our Environment What causes winds to blow? Is weather a sensitive or a non-sensitive system? Do you think that the Earth’s environment is a sensitive or a non-sensitive system? 13-1 Motion and Newton’s Laws Why can we predict the motion of the cart? The cart’s motion follows Newton’s Laws 1. An object remains at rest or moves at constant speed in a straight line unless a net force acts on it. 2. If forces act on an object, and if the forces do not balance one another, the object experiences a net force and accelerates. Force = Mass x acceleration 3. If one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. 4. Near the Earth, the force of gravity is Force = Mass x g where g = 9.8 m/s2 13-2 Deterministic Systems • A system is a sequence of events and a set of rules that define the events and any relation between these events. • In a deterministic system, there is a welldefined relation between successive events. • Each successive event may be determined from previous events. • All systems in nature are deterministic. • If we know all of the equations that govern the behavior of any system, the subsequent behavior of that system can be determined by previous events. 13-3 Sensitive Systems ♦ Some deterministic systems are inherently sensitive to the initial conditions of the event, such as the initial position or velocity of an object. ♦ In sensitive systems, small changes to initial conditions can result in large differences in outcomes. ♦ Two similar sensitive systems that start off with very similar initial conditions can behave very differently after a short time. ♦ This is known as the butterfly effect. 13-4 Predictable and Unpredictable Systems What is the difference between a system that is predictable and one that is not predictable? ♦ A predictable system is one that is not greatly affected by (is not sensitive to) the choice of the system’s initial conditions. ♦ An unpredictable system’s behavior is sensitive to its initial conditions. ♦ The outcomes of a non-sensitive system are predictable. But the outcomes of a sensitive system are not predictable 13-4a The Water Cycle • Water from the soil, rivers, lakes, and oceans is evaporated by the sun’s energy into water vapor. • When water vapor in the atmosphere cools sufficiently, it condenses to form clouds. • Precipitation from clouds brings the water back to the ground. 13-5 Why Do Winds Blow? Global wind patterns are produced by 1) the spinning of the Earth, which produces the Coriolis effect and 2) the uneven heating of the Earth’s surface, which causes convection currents. ♦ Heated air at the equator rises to higher latitudes. ♦ Cooler air from higher latitudes flows toward the equator. ♦ This convection mixes warm equatorial air with cooler high latitude air. 13-6 What Causes Land and Sea Breezes? ♦ During the day, the land heats up more quickly than the water. ♦ Air above the land is heated and rises, creating a region of low pressure above the shore. ♦ Air above the water moves inland toward the region of low pressure. This circulation creates convection currents. ♦ At night, the land cools off more quickly than the water. Warm air above the water rises, creating a region of low pressure above the water. ♦ Air from the land moves seaward toward the region of low pressure. ♦ The night time breeze moves in the opposite direction (out to sea) as the day time breeze. 13-6a Computer Simulations and Probabilities How could a simulation program such as Balance of the Planet be used to develop a series of probable outcomes? ♦ A computer program is run many times with slightly different initial conditions. ♦ If the results form clusters, you can turn those clusters into probabilities. ♦ Example: If a simulation gives a particular result 10% of the time, then that result has a 10% probability of occurring, according to this simulation. Note: The outcome of a sensitive system (sometimes called a chaotic system) is too uncertain to discuss in other than probabilities, such as a 40% predicted chance of rain tomorrow. 13-7 Period 13 Summary 13.1: Energy Balance of the Earth: The total energy in from the Sun must equal the total energy radiated out to prevent the Earth from heating up. 13.2 Water Cycle: Water from oceans and lakes evaporates when the Sun’s energy warms the water. Water vapor rises, is cooled, and condenses, forming clouds. When clouds become saturated, precipitation falls as rain or snow. Precipitation eventually runs back into lakes and oceans and the cycle repeats. Winds: Heated air at the equator rises to higher latitudes. Cooler air from higher latitudes flows toward the equator, causing convection currents. The spinning of the Earth (Coriolis effect) also produces global wind patterns. Land and sea breezes occur because land surfaces heat up and cool off more quickly than water surfaces, causing convection. 13.3 Biomass: Energy sources derived from plant and animals. Examples: alcohol used as fuel, and fossil fuels (coal, gas, oil). Period 13 Summary, continued 13.4 A system is a sequence of events and a set of rules that define the possible events and any relation between events. In a deterministic system, there is a welldefined relation between successive events. Each successive event may be determined from previous events. Some deterministic systems are sensitive to the initial conditions of the event. In sensitive systems, small changes to initial conditions can result in large differences in outcomes. (butterfly effect) The outcome of a sensitive system is too uncertain to discuss in other than probabilities. 13.5 Computer simulations can be used to develop a series of probable outcomes. A program is run many times with slightly different initial conditions. If the results form clusters, you can turn those clusters into probabilities. Example: If a simulation gives a particular result 10% of the time, then that result has a 10% probability of occurring, according to the simulation. Period 13 Review Questions R.1 What is the energy balance of the earth? What could happen if this balance is upset? R.2 What is the water cycle? How does solar energy play a role in the water cycle? R.3 What is biomass? What are some advantages of using biomass as fuel? R.4 What could happen to the outcome of a sensitive system that experiences small changes in its initial conditions? R.5 In what circumstances are computer simulations useful? What are some of the limitations of computer simulations?