Niigata Public High School Entrance Examination - Science flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Average speed

Distance travelled divided by the time taken, with no direction given. A car covering 120 km in 2 hours has an average speed of 60 km/h, even if its speed varied.

Newton's second law

The acceleration of an object equals the net force acting on it divided by its mass, written F = ma. Doubling the net force doubles the acceleration; doubling the mass halves it.

Work and energy

Work equals force times distance moved along the force, measured in joules. Doing work transfers energy, and with no friction the work done equals the change in kinetic or potential energy.

Conservation of mechanical energy

When friction and air resistance are negligible, the sum of kinetic energy and gravitational potential energy stays constant. A falling ball converts ½mv² into mgh and back.

Pressure in solids

Pressure equals force divided by the area over which it acts, measured in pascals. The same force over a smaller area gives greater pressure, so a drawing pin's point presses in easily.

Ohm's law

For a metallic conductor at constant temperature, voltage equals current times resistance, V = IR. Resistance is measured in ohms, and doubling voltage doubles current.

Series circuit rules

In a series circuit the current is identical at every point, the total resistance is the sum of the resistances, and the supply voltage divides among components in proportion to their resistance.

Parallel circuit rules

In a parallel circuit the voltage is the same across each branch, the total current is the sum of branch currents, and the combined resistance is smaller than the smallest branch resistance.

Electric power

Power equals voltage times current, P = VI, and also equals I²R or V²/R, measured in watts. Electrical energy used is power multiplied by time, often in kilowatt-hours.

Electromagnetic induction

Moving a magnet into or out of a coil induces a voltage in the coil. Faster movement, a stronger magnet, or more turns increase the induced voltage; this is the generator principle.

Wave equation

Wave speed equals frequency times wavelength, v = fλ. Frequency is determined by the source and stays constant when a wave crosses into another medium, but speed and wavelength change.

Physical versus chemical change

A physical change alters state, shape, or size with no new substance formed, such as melting or dissolving. A chemical change forms new substances, shown by colour change, gas, precipitate, or heat.

Distillation

A separation method that boils a liquid mixture and condenses the vapour. It separates a solvent from dissolved solids or liquids with clearly different boiling points, such as ethanol from water.

Density as identification

Density equals mass divided by volume, in g/cm³. Because each pure substance has its own density at a given temperature, measuring it helps identify the substance.

Neutralisation

The reaction of an acid with a base producing a salt and water. Hydrogen ions and hydroxide ions combine to form water, so the solution moves towards pH 7 and the temperature rises.

Oxidation and reduction

Oxidation adds oxygen to a substance and reduction removes it. In the blast furnace, carbon removes oxygen from iron oxide, so the iron oxide is reduced to iron metal.

Atomic structure

An atom has a small positive nucleus containing protons and neutrons, surrounded by electrons. The number of protons is the atomic number and determines which element the atom is.

Isotopes

Atoms of the same element with equal proton numbers but different neutron numbers, so they have different mass numbers. Their chemical properties are nearly identical because electron arrangements match.

Ion formation

An ion is a charged atom or group formed by gaining or losing electrons. Metal atoms lose electrons to become positive cations; non-metal atoms gain electrons to become negative anions.

Balancing equations

Adjust only the coefficients in front of formulas until each element has the same number of atoms on both sides. Never change subscripts, because that would change the substances involved.

The mole

One mole contains 6.0 × 10²³ particles and has a mass in grams equal to the molar mass. For example, 18 g of water is one mole of water molecules.

Electrolyte conduction

An ionic compound conducts electricity only when melted or dissolved, because its ions become free to move. A solid ionic crystal does not conduct, as its ions are fixed in place.

Energy flow in food chains

Energy enters a food chain through producers and passes to consumers, but only about ten percent reaches the next level. Most is lost as heat, so chains are short.

Decomposers

Organisms such as bacteria and fungi that break down dead bodies and waste, releasing carbon dioxide and mineral ions. These nutrients return to soil and water for producers to reuse.

Predator–prey cycles

A rise in prey numbers lets predators increase, which then reduces prey. The prey peak comes slightly before the predator peak, and the two populations oscillate around steady sizes.

Natural selection

Individuals with inherited variations suited to their environment survive and reproduce more, passing those traits on. Over many generations the favourable characteristic becomes common in the population.

Enzymes in digestion

Enzymes are proteins that speed up digestion of specific substrates: amylase breaks starch into sugars, protease breaks protein into amino acids, and lipase breaks fat into fatty acids and glycerol.

Villi

Finger-like folds covering the small intestine's inner wall. Their large surface area, thin walls, and dense blood capillaries allow fast absorption of digested nutrients into the blood.

Double circulation

Blood passes through the heart twice per circuit: the right side pumps to the lungs and the left side pumps around the body. This keeps oxygenated and deoxygenated blood separate.

Reflex arc

The pathway for a rapid automatic response: receptor, sensory neurone, spinal cord, motor neurone, muscle. The spinal cord can act without the brain, so the response is fast.

Plate boundaries

Divergent boundaries create new crust at mid-ocean ridges; convergent boundaries cause subduction, earthquakes, and volcanoes; transform boundaries slide past each other and cause earthquakes.

Seismic waves and the core

P waves arrive first and pass through solids and liquids; S waves arrive later and cannot pass through liquid. S-wave shadow zones show that the outer core is liquid.