General Physics – Scientific Measurements to Phase Change

A comprehensive set of question-and-answer flashcards covering measurement units, vectors, kinematics, dynamics, energy, fluids, thermodynamics, heat transfer and phase changes, designed for exam review.

What are the SI base units for length, mass and time?

Meter (m) for length, kilogram (kg) for mass, and second (s) for time.

Give the base-10 scientific prefix for 10⁶ and 10⁻⁶.

10⁶ → mega (M); 10⁻⁶ → micro (µ).

How many centimetres are in 25 inches? (1 in = 2.54 cm)

25 in × 2.54 cm/in = 63.5 cm.

Define a scalar quantity and give one example.

A scalar has magnitude only (no direction); e.g., mass = 5 kg.

Define a vector quantity and give one example.

A vector has both magnitude and direction; e.g., 60 mph north.

State the graphical ‘tail-to-head’ rule for adding vectors.

Place the tail of the second vector at the head of the first; the resultant is drawn from the tail of the first to the head of the last.

How do you subtract vector B⃗ from A⃗ graphically?

Reverse B⃗ to –B⃗ and add it to A⃗ using tail-to-head addition.

What is meant by the x- and y-components of a vector?

The projections of the vector onto the horizontal (x) and vertical (y) axes; they add vectorially to give the original vector.

Differentiate between speed and velocity.

Speed is a scalar (how fast); velocity is a vector (speed with direction).

Write the equation for average speed.

Average speed = total distance ÷ elapsed time.

What is the base unit of speed in SI?

Metres per second (m s⁻¹).

Define acceleration in words and as a formula.

Rate of change of velocity; a = (vf − vi)/Δt.

State the approximate magnitude of g near Earth’s surface.

9.8 m s⁻² (≈32 ft s⁻²) downward.

For an object in free fall, how much does its speed change each second (ignoring air)?

It increases by about 9.8 m s⁻¹ every second downward.

Write the free-fall distance formula for zero initial speed.

d = ½ g t².

Explain why horizontal velocity remains constant in ideal projectile motion.

Gravity acts vertically; there is no horizontal force (neglecting air resistance).

At what launch angle (no air resistance) is projectile range maximised?

45° above the horizontal.

State Newton’s First Law (law of inertia).

An object’s velocity remains constant unless acted on by a net external force.

Write Newton’s Second Law as an equation.

ΣF⃗ = m a⃗.

What is weight in terms of mass and g?

Weight W = m g, directed toward Earth’s centre.

Describe ‘apparent weight’ in an accelerating elevator.

It is the normal force the scale exerts; greater than mg during upward acceleration, less during downward acceleration.

State Newton’s Third Law.

For every action force, there is an equal and opposite reaction force acting on a different body.

Define static friction and kinetic friction.

Static friction prevents relative motion up to a limit; kinetic friction acts when surfaces slide, opposing motion.

What happens to net force and acceleration at terminal velocity?

Air resistance equals weight; net force and acceleration become zero.

Give the equation for linear momentum.

p⃗ = m v⃗.

State the impulse-momentum theorem.

Impulse J⃗ = F̅ Δt = Δp⃗.

State the law of conservation of momentum for an isolated system.

Total momentum before an interaction equals total momentum after.

Define mechanical work for a constant force parallel to displacement.

Work W = F d.

Give the formula for translational kinetic energy.

KE = ½ m v².

Write the expression for gravitational potential energy near Earth’s surface.

PE = m g h (relative to a reference level).

State the principle of conservation of mechanical energy (no non-conservative forces).

KE + PE = constant.

Define efficiency for a machine.

Efficiency (%) = 100 × (useful energy output) ÷ (energy input).

Write the formula that links density, mass and volume.

ρ = m / V.

How is pressure defined in fluids?

Pressure P = Force / Area, with SI unit Pascal (N m⁻²).

State Archimedes’ Principle.

A body wholly or partially immersed in a fluid experiences an upward buoyant force equal to the weight of fluid displaced.

Explain why ships float higher in salt water than in fresh water.

Salt water is denser, so less volume is needed to displace a weight equal to the ship’s mass.

State Bernoulli’s Principle in words.

Where the speed of a fluid increases, its internal pressure decreases (for steady, non-viscous flow).

Name the three common temperature scales and give their freezing points of water.

Celsius 0 °C, Fahrenheit 32 °F, Kelvin 273.15 K.

Convert 42 °C to Kelvin.

42 + 273.15 = 315.15 K.

What is absolute zero in Celsius?

−273.15 °C.

Define specific heat capacity.

Heat required per kilogram to raise temperature by 1 °C (unit J kg⁻¹ °C⁻¹).

Why does coastal climate stay more moderate than inland climate?

Water’s large specific heat absorbs/release large heat with small temperature change, regulating air temperature.

What is thermal expansion and give one everyday consequence.

Most substances expand when heated; e.g., power lines sag on hot days.

State the First Law of Thermodynamics.

ΔU = Q − W, i.e., energy added as heat equals increase in internal energy plus work done by the system.

What fundamental idea does the Second Law introduce?

Natural processes have a preferred direction; entropy of an isolated system never decreases.

State the Third Law of Thermodynamics.

It is impossible to reach absolute zero temperature by any finite number of processes.

Name the three modes of heat transfer.

Conduction, convection, and radiation.

Why are metals good thermal conductors?

Free electrons move energy rapidly through collisions.

Describe natural convection in terms of density.

Uneven heating creates density differences; warmer, less-dense fluid rises while cooler, denser fluid sinks, carrying heat.

What type of electromagnetic radiation does Earth mainly emit?

Long-wavelength infrared radiation.

Briefly explain the greenhouse effect.

Atmospheric CO₂ and water vapour absorb outgoing infrared radiation, trapping heat and raising Earth’s surface temperature.

Define latent heat of fusion.

Heat required per kilogram to change a solid to liquid (or released during freezing) at constant temperature.

What phase change is occurring when water at 100 °C absorbs heat without temperature rise?

Vaporisation/boiling; heat goes into latent heat of vaporisation.

Does evaporation cause cooling or heating of the remaining liquid? Why?

Cooling, because faster molecules escape, lowering average kinetic energy of the liquid.

Provide the latent heat formula for phase change.

Q = m L, where L is latent heat of fusion or vaporisation.

Explain why ice floats in water.

Ice is less dense than liquid water due to crystalline structure, so it displaces a weight of water equal to its own weight before being fully submerged.

Why does water exhibit anomalous expansion between 0 °C and 4 °C?

Hydrogen bonding causes open crystal structure in ice; upon warming to 4 °C this structure partially collapses, decreasing volume before normal expansion resumes.

In terms of Bernoulli’s principle, why can a roof lift off in high wind?

Wind over the roof speeds up, lowering pressure above; higher indoor pressure pushes the roof upward.

How does a bimetallic strip act as a thermostat switch?

Different expansion rates bend the strip when heated, opening or closing an electrical circuit at a set temperature.

Write the continuity equation for incompressible fluid flow.

A₁v₁ = A₂v₂ (cross-sectional area × speed is constant).

What is the difference between apparent weightlessness and true weightlessness?

Apparent weightlessness occurs when normal force is zero (e.g., free-fall elevator); true weightlessness would require no gravitational field.

What velocity must a low-Earth-orbit satellite have to stay in circular orbit?

Approximately 8 km s⁻¹ (about 18,000 mph).

Define escape speed from Earth and its value.

Minimum speed to leave Earth’s gravity without further propulsion; ≈ 11.2 km s⁻¹.

Why is kinetic friction usually less than maximum static friction?

Sliding surfaces spend less time interlocking their microscopic asperities than stationary surfaces.

Give the SI and British Engineering (BE) base units for force.

SI: Newton (N); BE: pound (lb).

If 1 lb = 4.48 N, what is 10 lb in Newtons?

10 lb × 4.48 N/lb = 44.8 N.

Provide the formula for pressure at depth h in a liquid of density ρ.

P = ρ g h + P_atm (if open to atmosphere).

Why does a helium balloon rise in air?

The buoyant force (weight of displaced air) exceeds the balloon’s weight because helium + envelope is less dense than air.