1. ST Mid-Year Overview

2. Combustion
The fire triangle illustrates the relationship between the three basic elements needed to establish fire: oxygen (O2), combustible fuel (a form of C and H), and heat to initiate and sustain combustion.
In the combustion process, oxygen “oxidizes” (combines with) carbon and hydrogen molecules as heat breaks chemical bonds during combustion. When vegetation is burned, heat is released in the form of thermal, radiant, and kinetic energy. Heat is supplied initially from an external source (lightning, matches, etc).
The general chemical equation for a combustion reaction:
(C, H compound) + O2 → CO H2O

3. Law of Conservation of Mass
For example, if you were told that 4 grams of hydrogen reacted with some oxygen to make 36 grams of water then you could figure out how much oxygen must have been used by applying the law of conservation of mass.
 If mass is conserved it means that the mass is always the same or does not change. The Law of Conservation of Mass applies to chemical changes. When considering a chemical change this would mean that the total mass of all of the reactants in the chemical reaction is equal to the total mass of products in the chemical reaction.
BALANCED EQUATIONS ARE NECESSARY!

4. Nitrogen Cycle – bacteria convert! N2 → NH3 → NO2- → NO3- → N2
NITROGEN FIXATION: N2 → NH3
NITRIFICATION: NH3 → NO2- (nitrites)
NO2- → NO3- (nitrates)
NITROGEN absorption: Plants absorb ammonium (NH4+ ) and nitrates (NO3-) from soil or water.
ANIMALS MUST EAT PLANTS or EAT OTHER ANIMALS to obtain nitrogen.
DECOMPOSITION: wastes → ammonium (NH4+)
DENITRIFICATION: NO3- → N2 for the atmosphere.

5. Carbon Cycle - Photosynthesis – plants
6 CO2 + 6 H2O + energy  6O2 + C6H12O6
Animals (herbivores) eat plants or animals (carnivores).
- Living organisms respire
6 O2 + C6H12O6  6 CO2 + 6 H2O + energy
Animal’s waste release CO2 + CH4.
Forest fires release CO2
- CO2 dissolves in water and reacts with calcium to become calcium carbonate. The carbonate rock comes to the surface through volcanic activity.
- Fossil fuels form from dead organisms that fall to the ocean floor and fossilize.

6. Magnetism
Straight wire conductor’s magnetic field. NORTH compass needles point the SOUTH pole.

7. Heat and Temperature
Heat is the total energy of molecular motion in a substance while temperature is a measure of the average energy of molecular motion in a substance. Heat energy depends on the speed of the particles, the number of particles (the size or mass), and the type of particles in an object.
Temperature does not depend on the size or type of object. For example, the temperature of a small cup of water might be the same as the temperature of a large tub of water, but the tub of water has more heat because it has more water and thus more total thermal energy.
It is heat that will increase or decrease the temperature. If we add heat, the temperature will become higher. If we remove heat the temperature will become lower. Higher temperatures mean that the molecules are moving, vibrating and rotating with more energy.

8. Energy Resources

9. FOSSIL FUELS NUCLEAR ENERGY Coal is crushed to a fine dust and burnt.
Oil and gas can be burnt directly.
NUCLEAR ENERGY

10. WIND ENERGY
We can use the energy in the wind by building a tall tower, with a large propellor on the top.
The wind blows the propellor round, which turns a generator to produce electricity.
TIDAL POWER - A huge dam (called a "barrage") is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam. - The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine.

11. sOLAR ENERGY 1) Solar Cells (really called "photovoltaic” or "photoelectric" cells) that convert light directly into electricity. 2) Solar Furnaces use a huge array of mirrors to concentrate the Sun's energy into a small space and produce very high temperatures. 3) Solar water heating, where heat from the Sun is used to heat water in glass panels on your roof.

12. HYDROELECTRICTY
A dam is built to trap water, usually in a valley where there is an existing lake.
Water is allowed to flow through tunnels in the dam, to turn turbines and thus drive generators.
Hydro-electric power stations can produce a great deal of power very cheaply.

13. TIDES – The Earth-Moon System
Point A is the surface of the ocean nearest the moon; point C is farthest from the moon; point B is the center of the earth.
The arrows in the top diagram pointing toward the moon represent the force of the moon's gravity at these three points. 
Point A is attracted to the moon most strongly, point C least strongly, and point B at intermediate strength.
The lines leading downward from each point show how each point would move under the influence of the moon's gravity. 
Point A moves farthest toward the moon, B, not as far, and C least of all.  The result is as if the ocean were bulging out toward and away from the moon.  Thus, as the earth rotates under this bulge, any point on earth has two high tides and two low tides each day.

14. Don’t forget the mechanical and electrical engineering topics!