General Science: Physics, Chemistry and Biology Essentials
General Science is school-level physics, chemistry and biology applied to farm and daily life.
Physics
- SI units: metre, kilogram, second, newton for force, joule for energy, watt for power.
- Speed is distance divided by time and is a scalar; velocity carries direction and is a vector. Work is force multiplied by displacement; power is work divided by time.
- Light travels in straight lines, reflects and refracts; concave mirrors converge, convex lenses converge. Power of a lens is 1 divided by focal length in metres.
- Ohm's law V = IR, with volt, ampere and ohm as units; household wiring is in parallel.
Chemistry
- An atom has protons and neutrons in the nucleus and electrons outside. Atomic number equals the number of protons; mass number equals protons plus neutrons.
- Acids turn blue litmus red, bases turn red litmus blue; pH 7 is neutral, below 7 acidic, above 7 basic.
- Common compounds: common salt NaCl, limestone CaCO3, gypsum CaSO4 with two water molecules, urea CO(NH2)2 supplying 46% N.
Biology
- Plant cells have a cell wall; photosynthesis in chloroplasts converts carbon dioxide and water into glucose and oxygen using chlorophyll and sunlight.
- Human systems to revise: digestive, circulatory with blood groups, respiratory, nervous and excretory.
- Vitamins and deficiency diseases: A for night blindness, B1 for beriberi, C for scurvy, D for rickets, K for clotting.
Worked example
A tractor covers 60 km in 45 minutes. Convert time first: 45 minutes = 0.75 hours. Speed = 60 divided by 0.75 = 80 km per hour. In metres per second, 80 multiplied by 5/18 is about 22.2 m per second.
Traps
- Using mass and weight interchangeably; weight equals mass multiplied by gravity.
- Saying atomic number equals the number of neutrons.
- Forgetting the 5/18 factor when converting km per hour to metres per second.