NCEA L1 Physics & ESS flashcards

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

Scalar vs vector

A scalar has magnitude only (speed, mass, energy). A vector has magnitude and direction (velocity, force, acceleration). Direction matters when adding vectors, so 3 m north plus 4 m east gives 5 m, not 7 m.

Average speed

Total distance travelled divided by total time taken. It is not the mean of the speeds for each part of a journey, because faster sections cover more distance in the same time.

Velocity–time graph gradient

The slope of a velocity–time graph equals acceleration. A horizontal line means constant velocity (zero acceleration); a line sloping down toward the time axis means deceleration.

Velocity–time graph area

The area between the line and the time axis equals displacement. Areas below the axis count as negative displacement, so the total displacement is the net area.

Newton's second law

The net force on an object equals its mass times its acceleration, F = ma. Doubling the net force doubles acceleration; doubling the mass halves it for the same force.

Weight versus mass

Mass is the amount of matter in kilograms and is unchanged by location. Weight is the gravitational force on that mass, W = mg, measured in newtons, so it changes with gravity.

Balanced forces

When the forces on an object add to zero, the net force is zero. The object stays at rest or moves at constant velocity; it does not necessarily stop.

Work done

Work equals force times displacement in the direction of the force, measured in joules. A force perpendicular to motion, such as a horizontal push on a load carried level, does no work.

Power

Power is the rate of transferring energy, P = W ÷ t, measured in watts. One watt is one joule per second; a 60 W lamp transfers 60 J each second.

Kinetic energy

The energy of a moving object, E_k = ½mv², in joules. Because velocity is squared, doubling speed quadruples kinetic energy, which is why stopping distances rise sharply.

Conservation of energy

Energy cannot be created or destroyed, only transferred or transformed. In a falling object, gravitational potential energy becomes kinetic energy, with some lost to friction and air resistance.

Ohm's law

For an ohmic conductor at constant temperature, voltage equals current times resistance, V = IR. Resistance in ohms equals voltage in volts divided by current in amperes.

Series circuit rules

Components in one loop share the same current. The supply voltage is shared between them and total resistance is the sum: R_total = R₁ + R₂.

Parallel circuit rules

Components on separate branches have the same voltage across them. Branch currents add to give the total, and total resistance is less than the smallest single resistance.

Electrical power formulas

Power in a circuit is P = VI, also written P = I²R or P = V²/R. A 12 V device drawing 2 A uses 24 W.

Kilowatt-hour

A unit of energy equal to 3.6 million joules, used on electricity bills. A 1 kW appliance running for 1 hour uses 1 kWh; running for 3 hours uses 3 kWh.

Earth's layered structure

Earth has a thin rocky crust, a solid mantle, a liquid outer core and a solid inner core. The iron-rich core generates the magnetic field through motion of conducting liquid metal.

Seismic wave evidence

P-waves (compressional) travel through solids and liquids; S-waves (transverse) cannot pass through liquids. S-wave shadow zones prove the outer core is liquid.

Divergent plate boundary

Plates move apart and magma rises to fill the gap, forming new crust. Examples are mid-ocean ridges and rift valleys, with shallow earthquakes and volcanic activity.

Convergent plate boundary

Plates move toward each other. Oceanic crust subducts beneath continental crust, forming trenches, volcanoes and fold mountains, and producing deep earthquakes.

Transform plate boundary

Plates slide past each other horizontally without creating or destroying crust. Stress builds until it releases as earthquakes, as along the Alpine Fault in New Zealand.

Rock cycle

The set of processes that change rock between igneous, sedimentary and metamorphic types. Melting, cooling, weathering, deposition, compaction and heat and pressure drive the changes.

Igneous rock

Rock formed when molten magma or lava cools and solidifies. Slow cooling underground makes large crystals (granite); rapid cooling at the surface makes fine crystals (basalt).

Sedimentary rock

Rock formed from layers of sediment compacted and cemented over time, often containing fossils. Limestone and sandstone are examples; the layers are called strata.

Earthquake focus and epicentre

The focus is the point underground where rupture releases energy. The epicentre is the point on the surface directly above it, usually where shaking is strongest.

Cause of seasons

Earth's axis is tilted about 23.5°, so each hemisphere receives sunlight at a different angle and for different day lengths through the year. Distance from the Sun is not the cause.

Rotation versus revolution

Rotation is Earth spinning on its axis, causing day and night and taking about 24 hours. Revolution is orbiting the Sun, taking about 365.25 days and defining the year.

Tidal locking

The Moon rotates once per orbit, so the same hemisphere always faces Earth. This happens because Earth's gravity has slowed the Moon's spin over a long time.

Phases of the Moon

The changing visible shape of the Moon as it orbits Earth, caused by varying angles of sunlight. The cycle from new Moon to new Moon takes about 29.5 days.

Solar eclipse

An eclipse occurring when the Moon passes between the Sun and Earth at new Moon, casting a shadow on Earth. It is visible only along a narrow path.

Lunar eclipse

An eclipse occurring when Earth passes between the Sun and the Moon at full Moon, so Earth's shadow falls on the Moon. It is visible from the whole night side of Earth.

Star versus planet

A star produces its own light by nuclear fusion in its core. A planet shines by reflected starlight, orbits a star, and is massive enough to be roughly spherical.