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Natural Science: free practice, theory and problems
Science is a way of finding out how the world works: we ask questions, make hypotheses and test them with experiments and observations.
Contents
- The scientific method
- Energy and energy sources
- Climate and sustainability
- Radiation and radioactivity
- Health and the body
- Everyday chemistry
1. The scientific method
What is it about?
Science is a way of finding out how the world works: we ask questions, make hypotheses and test them with experiments and observations.
Concepts and formulas
- Hypothesis: a possible explanation that can be tested.
- Variables: the one you change (independent), the one you measure (dependent) and the ones you keep the same (controlled).
- Control group: a group that does not get the "treatment", so you have something to compare with.
- Reproducibility: others should be able to repeat the experiment and get the same result.
- Peer review: other scientists assess the work before it is published.
- Correlation is not the same as causation: two things can go together without one causing the other.
Example
You test whether fertiliser gives taller plants. Independent variable: amount of fertiliser. Dependent: plant height. Controlled: light, water, soil and plant species.
2. Energy and energy sources
What is it about?
All activity needs energy. Energy cannot be created or destroyed, only converted from one form to another. The questions are where it comes from and how much is lost as heat.
Concepts and formulas
- Conservation of energy: the total energy is constant.
- Forms of energy: kinetic (motion), potential (height), chemical, electrical, thermal (heat), radiant.
- Efficiency: . The rest becomes heat.
- Power: energy per time, . Unit watt (W) = J/s. 1 kWh = 3.6 MJ.
- Renewable sources: hydro, wind, solar, waves, bioenergy. Non-renewable: oil, gas, coal and uranium.
- Norway gets most of its electricity from hydropower.
Example
A light bulb uses 60 J and gives 6 J of light. The efficiency is . The rest becomes heat.
3. Climate and sustainability
What is it about?
Earth's climate is governed by the balance between energy coming in from the Sun and energy radiated out. Greenhouse gases retain heat. More greenhouse gases give global warming.
Concepts and formulas
- The greenhouse effect: gases such as , methane and water vapour let sunlight in but hold back part of the heat radiation from Earth. Without the natural greenhouse effect Earth would average about −18 °C.
- Human-caused warming comes mainly from burning coal, oil and gas, and from deforestation.
- The carbon cycle: carbon moves between the atmosphere, the ocean, plants, soil and fossil stores.
- Weather is what happens now. Climate is the average weather over at least 30 years.
- Sustainable development (the Brundtland Commission, 1987): meeting today's needs without destroying the options of future generations.
- The Paris Agreement (2015): keep warming well below 2 °C, and preferably 1.5 °C.
Example
When the ocean warms, the water expands and glaciers melt. Both make sea level rise.
4. Radiation and radioactivity
What is it about?
Radiation is energy sent out as waves or particles. Some radiation is harmless (radio, visible light), while ionising radiation can damage cells and DNA.
Concepts and formulas
- The electromagnetic spectrum (long to short wavelength): radio, microwaves, infrared, visible light, UV, X-rays, gamma rays. Shorter wavelength = more energy.
- Ionising radiation: UV (partly), X-rays, gamma and particle radiation. It can knock electrons off atoms.
- Radioactive radiation: alpha (helium nuclei, stopped by paper), beta (electrons, stopped by a few mm of aluminium), gamma (partly stopped by thick lead or concrete).
- Half-life: the time it takes for half of the nuclei to decay.
- Radon from bedrock is the largest source of radiation in Norwegian homes.
- Radiation is also useful: X-ray images, radiotherapy for cancer, sterilisation.
Example
A substance has a half-life of 8 days. After 24 days remains.
5. Health and the body
What is it about?
The body needs nutrition, sleep and exercise. Food provides energy and building blocks, and the immune system protects us from disease.
Concepts and formulas
- Nutrients: carbohydrates (energy), fat (energy and storage), proteins (building blocks), vitamins, minerals and water.
- Energy content: 1 g of carbohydrate or protein ≈ 17 kJ, 1 g of fat ≈ 37 kJ.
- Energy balance: if you eat more energy than you use, the rest is stored as fat.
- Pathogens: bacteria (treatable with antibiotics), viruses (no antibiotics), fungi and parasites.
- Vaccines teach the immune system to recognise a pathogen.
- Antibiotic resistance: bacteria become resistant when antibiotics are overused or misused.
- Lifestyle diseases: for example type 2 diabetes and cardiovascular disease.
Example
A packed lunch has 30 g carbohydrate, 10 g fat and 15 g protein. Energy: kJ.
6. Everyday chemistry
What is it about?
Everything around us is chemistry: the food we cook, cleaning products, plastic and batteries. Substances are made of atoms bonding into molecules and compounds.
Concepts and formulas
- Atom: a nucleus of protons and neutrons, with electrons around it. Element: only one type of atom.
- The periodic table orders the elements by number of protons.
- Chemical reaction: substances become new substances. Atoms do not disappear (conservation of mass).
- The pH scale: below 7 is acidic, 7 is neutral, above 7 is basic. Each step is a factor of 10.
- Acid + base gives salt and water (neutralisation).
- Organic chemistry: substances containing carbon, like plastic, sugar and fuel.
- Safety data and hazard symbols show how chemicals are to be handled safely.
Example
Vinegar has a pH of about 3 and soap about 10. pH 3 is times more acidic than pH 7.
Example problems with solutions
Here are some of the problems in natural Science. In the app, calculation problems get new numbers every time, so you can practise until it sticks – and take a graded practice exam before the real one.
The scientific method: What is a hypothesis?
Answer: A possible explanation that can be tested
The hypothesis is tested by experiment.
Energy and energy sources: Which energy source gives the most electricity in Norway?
Answer: Hydropower
Around 90 % of Norwegian electricity comes from hydropower.
Climate and sustainability: What is the difference between weather and climate?
Answer: Climate is the average weather over at least 30 years
Weather is now, climate is over time.
Radiation and radioactivity: Which radiation is stopped by a sheet of paper?
Answer: Alpha radiation
Alpha particles are large and heavy.