Foundation - a strong base in Physics, Chemistry, Maths & Biology

What it is

Pressure is how concentrated a force is - the same push on a smaller area presses much harder.

Answer

Pressure is the force acting on a unit area, P = F/A. A sharp knife has a very small area at its edge, so for the same force the pressure it exerts is much greater, and it cuts easily. A blunt knife has a larger edge area, so the same force produces less pressure and cuts poorly.

What it is

Friction is the grip between two surfaces that resists sliding.

Answer

Friction is called a necessary evil because it is both useful and harmful. It is necessary as it lets us walk, hold objects, write and stop vehicles. It is an evil because it wears out machine parts and shoe soles and produces heat that wastes energy. So we increase it where needed (treads, brakes) and reduce it where it wastes energy (lubricants, ball bearings).

What it is

Sound is a vibration that travels by shaking the particles of a medium.

Answer

Sound is produced by vibrating objects; the vibrations push the particles of the surrounding medium, creating compressions and rarefactions that travel outward as a wave. Sound needs a material medium (solid, liquid or gas) because it moves by making particles vibrate. In a vacuum there are no particles, so sound cannot travel.

What it is

Electroplating uses electricity to coat one metal with a thin layer of another.

Answer

Electroplating is the process of depositing a layer of one metal over another using electricity (the chemical effect of electric current). When current passes through a solution of a metal salt, metal ions are deposited on the object connected to the negative terminal. It is used to coat iron with chromium or nickel to prevent rusting and to make cheap ornaments look like gold or silver.

What it is

Metals are shiny, bendable conductors of heat and electricity; non-metals are dull, brittle insulators.

Answer

Metals are generally lustrous (shiny), malleable and ductile, good conductors of heat and electricity, and sonorous. Non-metals are usually dull, brittle (break easily) and poor conductors of heat and electricity. For example, iron is a shiny conductor while sulphur is a dull, brittle insulator.

What it is

Burning needs three partners together: fuel, oxygen and enough heat.

Answer

For combustion, three things must be present together: a combustible substance (fuel), a supporter of combustion (usually oxygen from air) and heat to raise the fuel to its ignition temperature. If any one is removed, burning stops - which is why covering a fire with a blanket (cutting off oxygen) or water (cooling below the ignition temperature) puts it out.

What it is

Coal and petroleum are fuels formed from ancient buried life over millions of years.

Answer

Coal and petroleum are called fossil fuels because they were formed from the dead remains of prehistoric plants and animals buried under the earth for millions of years under high heat and pressure. They are exhaustible natural resources - they take millions of years to form but are being used up fast - so they must be conserved and used carefully.

What it is

Most plastics do not rot (they are non-biodegradable), so they pile up for centuries.

Answer

Most plastics are non-biodegradable, which means micro-organisms cannot break them down, so they stay in the environment for hundreds of years. Burning plastic releases harmful gases, and discarded plastic chokes drains, harms animals that swallow it and pollutes soil and water. The best approach is to reduce, reuse and recycle plastic.

What it is

Plant cells have a cell wall, a big vacuole and chloroplasts; animal cells have none of these.

Answer

A plant cell has a rigid cell wall outside its cell membrane and usually contains a large central vacuole and green chloroplasts for photosynthesis. An animal cell has no cell wall (only a cell membrane), has small or no vacuoles and lacks chloroplasts. This is why plants can make their own food while animals cannot.

What it is

Microbes are tiny living things that can help us (curd, bread, medicine) or harm us (disease).

Answer

Useful: yeast is used to make bread and in brewing (fermentation), and Lactobacillus bacteria turn milk into curd. Harmful: the bacterium that causes tuberculosis, and the Plasmodium protozoan that causes malaria. So micro-organisms can help or harm us depending on the type.

What it is

Manure is natural and releases nutrients slowly; fertiliser is a chemical that acts fast.

Answer

Manure is a natural substance made by decomposing animal dung and plant waste; it adds humus, improves soil texture and releases nutrients slowly. A fertiliser is a chemical made in factories that is rich in a specific nutrient (like nitrogen, phosphorus or potassium) and acts fast, but its overuse can harm the soil and water. Manure is eco-friendly; fertilisers give a quick nutrient boost.

What it is

At puberty, hormones bring body changes that mark a child becoming an adult.

Answer

Secondary sexual characters are the physical features that appear at puberty and distinguish males from females - such as growth of facial hair and deepening of the voice in boys, and development of breasts in girls. They are controlled by hormones released by the endocrine glands: testosterone from the testes in boys and oestrogen from the ovaries in girls.

What it is

Solving an equation means undoing the operations to leave the unknown by itself.

Answer

Subtract 5 from both sides: 3x = 20 - 5 = 15. Divide both sides by 3: x = 15/3 = 5. So x = 5. Check: 3(5) + 5 = 15 + 5 = 20, which is correct.

What it is

A square root asks: which number multiplied by itself gives this number?

Answer

Factorise: 1225 = 5 x 5 x 7 x 7 = 5^2 x 7^2. Pair the equal factors and take one from each pair: sqrt(1225) = 5 x 7 = 35. So the square root of 1225 is 35.

What it is

Standard form writes very large or very small numbers as a x 10^n.

Answer

Move the decimal point to just after the first non-zero digit to get 7.3. The point moved 6 places to the right, so we multiply by 10 raised to the power -6. Therefore 0.0000073 = 7.3 x 10^-6.

What it is

Profit percent measures your gain compared with the cost price, not the selling price.

Answer

Profit = selling price - cost price = 575 - 500 = 75 rupees. Profit percent = (profit / cost price) x 100 = (75 / 500) x 100 = 15 percent. So the shopkeeper makes a 15 percent profit.

What it is

Reflection is light bouncing off a surface following two fixed rules.

Answer

First law: the incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane. Second law: the angle of incidence is always equal to the angle of reflection (i = r).

What it is

Greenhouse gases act like a blanket that traps the Sun's heat around the Earth.

Answer

The greenhouse effect is the trapping of the Sun's heat near the Earth's surface by gases like carbon dioxide, methane and water vapour, which keeps the planet warm enough for life. It becomes a concern when human activities release extra greenhouse gases, trapping too much heat and causing global warming and climate change.

What it is

Animals either lay eggs (oviparous) or give birth to live young (viviparous).

Answer

Oviparous animals lay eggs that develop and hatch outside the mother's body, for example a hen or a frog. Viviparous animals give birth to live young that develop inside the mother's body, for example a human or a cow.

What it is

Algebraic identities are shortcuts that expand or factor expressions instantly.

Answer

Use the identity (a + b)^2 = a^2 + 2ab + b^2 with a = x and b = 5. So (x + 5)^2 = x^2 + 2(x)(5) + 5^2 = x^2 + 10x + 25.

What it is

Lightning is a huge electric spark between charged clouds or between a cloud and the ground.

Answer

During a thunderstorm, air currents make the top of a cloud positively charged and the bottom negatively charged. When the charge grows large enough it jumps as a giant spark - lightning - to another cloud or to the ground. A lightning conductor is a metal rod fixed at the top of a building and connected to the earth; it safely carries the lightning's charge into the ground and protects the building.

What it is

A good fuel gives lots of heat, is cheap, easy to store and burns cleanly.

Answer

A good fuel should have a high calorific value (release a large amount of heat per kilogram), a moderate ignition temperature, be readily available and cheap, be easy to store and transport, and burn without leaving much ash or releasing harmful smoke. For example, LPG is a good domestic fuel because it has a high calorific value and burns cleanly.

What it is

Biodiversity is the variety of all living things - plants, animals and microbes - in an area.

Answer

Biodiversity is the variety of living organisms - plants, animals and micro-organisms - found in a particular area. It should be conserved because every species has a role in keeping the ecosystem balanced, and the loss of one can affect many others. Biodiversity gives us food, medicines, and clean air and water, and losing it through deforestation and pollution can push species to extinction.

What it is

A trapezium's area is the average of its two parallel sides times the height.

Answer

Area of a trapezium = (1/2) x (sum of parallel sides) x height = (1/2) x (12 + 8) x 5 = (1/2) x 20 x 5 = 50 square cm.