Science 24

The materials and energy we use daily — gasoline, natural gas, cleaning products, plastics, batteries — are made by technological processes that turn raw matter into something useful.

Conservation of mass means atoms are never created or destroyed in a reaction — the total mass of the reactants equals the total mass of the products.

These processes give us convenience and jobs, but they also use resources and produce waste, so the same product has both benefits and costs.

Because atoms must be equal on both sides, we balance an equation by adjusting the big coefficients in front, e.g. $\text{CH}_4 + 2\,\text{O}_2 \rightarrow \text{CO}_2 + 2\,\text{H}_2\text{O}$ has the same atoms left and right.

A chemical reaction is signalled by observable clues — a colour change, gas bubbles, heat or light, or a new solid — that tell you a new substance formed.

Energy comes in forms — electrical, heat (thermal), light, sound, motion (kinetic), chemical — and devices transform it from one form to another (a toaster: electrical → heat; a flashlight: chemical → light).

An electrical device converts electrical energy into a useful form: a bulb into light, a motor into motion, a heater into heat, a speaker into sound.

Chemical energy is stored in the bonds of fuels and food; a reaction releases it — burning propane releases heat and light, and a battery releases electrical energy.

A single device often makes several transformations at once: a hair dryer turns electrical energy into motion (the fan), heat (the coil) and sound.

Naming the conversion is the first step to understanding a device — it tells you what the device is FOR and what form of energy you are paying for.

Health is shaped by more than personal choices: diet, income, housing, stress, clean air and water, and access to health care all influence how healthy a person or community is.

The body has layered defences: barriers that keep pathogens out (skin, mucus, stomach acid, tears) and internal defences that attack anything that gets in (white blood cells, fever, the immune response).

These factors explain why one neighbourhood or country can be far healthier than another even when individuals make similar choices — the surroundings matter.

After fighting off some pathogens the immune system "remembers" them, giving immunity — which is also how vaccines work: they train the defences without causing the disease.

Because many health factors are set by society (not the individual), improving health often needs collective action — safe water, sewage systems, food inspection, vaccination programs, workplace safety rules.

A scientific statement is backed by evidence and can be tested; a personal opinion is a belief or preference that may not be — telling them apart is essential when judging safety claims.

Speed is how fast position changes: $v = \frac{d}{t}$, measured in metres per second or km/h — a car covering $100\ \text{km}$ in $2\ \text{h}$ averages $50\ \text{km/h}$.

Momentum is mass in motion, $p = mv$ — a heavy or fast object has more momentum, which is why a loaded truck is far harder to stop than a bike at the same speed.

Explanatory models from science (how bodies and vehicles actually move) let you check a claim against evidence instead of just how it feels.

The same formula rearranges to find distance ($d = vt$) or time ($t = \frac{d}{v}$), so from any two of the three you can find the third.