IB Physics HL
Comprehensive flashcards for IB Diploma Programme Physics at Higher Level (2025 syllabus, first exams 2025). Covers all five themes (A: Space, time and motion; B: The particulate nature of matter; C: Wave behaviour; D: Fields; E: Nuclear and quantum physics) including the full SL core plus all Additional Higher Level (AHL) extensions, with Nature of Science and experimental skills.
Ämne: Fysik · Nivå: Gymnasium (16–19) · 495 kort
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- Displacement is the straight-line distance and direction from start to finish (a vector). Distance is the total path length travelled (a scalar).
- Velocity is the rate of change of displacement (a vector). Speed is the rate of change of distance (a scalar). Units: m s⁻¹.
- Acceleration is the rate of change of velocity (a vector): a = Δv/Δt. Units: m s⁻². A change in direction at constant speed is still an acceleration.
- The four SUVAT equations of uniformly accelerated motion: v = u + at; s = ut + ½at²; v² = u² + 2as; s = ½(u+v)t. They apply only when acceleration is constant.
- On a displacement-time graph the gradient gives velocity. On a velocity-time graph the gradient gives acceleration and the area under the curve gives displacement.
- Free-fall acceleration near Earth's surface is g ≈ 9.81 m s⁻², directed downward. In the absence of air resistance all objects fall with the same acceleration regardless of mass.
- Projectile motion separates into independent horizontal and vertical components: horizontal velocity is constant (no horizontal force), vertical motion has constant acceleration g.
- For a projectile launched at speed u and angle θ: range on level ground R = u² sin(2θ)/g, maximum at θ = 45°. Time of flight = 2u sinθ/g.
- Air resistance (a fluid resistive force) acts opposite to motion and increases with speed. A falling object reaches terminal velocity when drag equals weight and net force is zero.
- Newton's first law: an object remains at rest or moves with constant velocity unless acted on by a net (unbalanced) external force. This defines the property of inertia.
- Newton's second law: net force equals rate of change of momentum, F = Δp/Δt. For constant mass this reduces to F = ma.
- Newton's third law: if body A exerts a force on body B, then B exerts an equal and opposite force on A. The two forces act on different bodies and are of the same type.
- A free-body diagram shows all external forces acting on a single object as arrows from the object, with direction and relative magnitude. Internal forces and forces the object exerts on others are excluded.
- Weight is the gravitational force on a mass: W = mg. It is a force measured in newtons, distinct from mass which is measured in kilograms and is constant.
- The normal force (normal reaction) is the contact force exerted by a surface perpendicular to that surface. It is not always equal to weight — it depends on the other forces present.
- Static friction (up to a maximum F ≤ μₛR) prevents relative motion; kinetic (dynamic) friction (F = μₖR) opposes existing sliding. Generally μₛ > μₖ.
- Translational equilibrium occurs when the resultant force on a body is zero, so it remains at rest or moves with constant velocity (Newton's first law).
- Hooke's law: the force from an ideal spring is F = kx, where k is the spring constant (N m⁻¹) and x is the extension or compression from natural length. Valid up to the elastic limit.
- Linear momentum p = mv is a vector with units kg m s⁻¹ (equivalently N s). The total momentum of a system points in the direction of net motion.
- Impulse is the change in momentum: J = FΔt = Δp (units N s). On a force-time graph, impulse equals the area under the curve.
- Conservation of linear momentum: in the absence of external forces, the total momentum of a system before a collision or explosion equals the total momentum after.
- In an elastic collision both momentum and kinetic energy are conserved. In an inelastic collision momentum is conserved but kinetic energy is not (some is converted to heat, sound, deformation).
- A perfectly inelastic collision is one in which the colliding bodies stick together and move with a common final velocity, losing the maximum kinetic energy allowed by momentum conservation.
- Work done by a constant force: W = Fs cosθ, where θ is the angle between force and displacement. Units: joules (J). No work is done when force is perpendicular to motion.
- Kinetic energy of a moving mass: Eₖ = ½mv². It also equals p²/(2m) in terms of momentum. Units: joules.
- Change in gravitational potential energy near Earth's surface: ΔEₚ = mgΔh, where Δh is the change in height. Valid where g is approximately constant.
- Elastic potential energy stored in a stretched/compressed spring: Eₑ = ½kx². This equals the area under the force-extension graph.
- The work-energy theorem: the net work done on an object equals its change in kinetic energy, W_net = ΔEₖ.
- Power is the rate of doing work or transferring energy: P = W/t = ΔE/t. For a force moving at velocity v, P = Fv. Units: watts (W), where 1 W = 1 J s⁻¹.
- Efficiency = useful output energy (or power) / total input energy (or power). It is a dimensionless ratio between 0 and 1, often expressed as a percentage. No real machine reaches 100%.
- An object in uniform circular motion moves at constant speed but is constantly accelerating because its velocity direction changes. The acceleration points toward the centre (centripetal).
- Centripetal acceleration: a = v²/r = ω²r, directed toward the centre. The centripetal force is F = mv²/r = mω²r. It is a net force, not a new kind of force.
- Angular velocity ω = Δθ/Δt = 2π/T = 2πf, measured in rad s⁻¹. Linear and angular speed are related by v = ωr.
- Newton's law of universal gravitation: F = GMm/r², an attractive force between any two point masses. G = 6.67×10⁻¹¹ N m² kg⁻² is the universal gravitational constant.
- Gravitational field strength g is the gravitational force per unit mass: g = F/m = GM/r². Units N kg⁻¹, numerically equal to free-fall acceleration in m s⁻².
- Kepler's third law: for objects orbiting the same central body, the square of the orbital period is proportional to the cube of the orbital radius, T² ∝ r³.
- For a satellite in circular orbit, gravity provides the centripetal force: GMm/r² = mv²/r, giving orbital speed v = √(GM/r). Speed depends only on the central mass and radius, not the satellite's mass.
- [HL] Torque (moment of a force) about an axis: τ = Fr sinθ, where r is the distance from the axis and θ the angle between force and lever arm. Units: N m. It causes angular acceleration.
- [HL] Moment of inertia I quantifies an object's resistance to angular acceleration. For a point mass I = mr²; for extended bodies I = Σmr². It depends on mass distribution about the axis.
- [HL] The rotational form of Newton's second law: net torque equals moment of inertia times angular acceleration, τ = Iα.
- [HL] Angular momentum L = Iω (units kg m² s⁻¹). It is conserved when no net external torque acts — which is why a spinning skater speeds up as she pulls her arms in (reducing I).
- [HL] Rotational kinetic energy: Eₖ(rot) = ½Iω². A rolling object has both translational (½mv²) and rotational kinetic energy.
- [HL] The rotational SUVAT-equivalent equations use angular quantities: ω = ω₀ + αt; θ = ω₀t + ½αt²; ω² = ω₀² + 2αθ. They hold for constant angular acceleration α.
- [HL] Einstein's two postulates of special relativity: (1) the laws of physics are identical in all inertial frames; (2) the speed of light in vacuum, c, is the same for all inertial observers regardless of the source's motion.
- [HL] The Lorentz factor γ = 1/√(1 − v²/c²) is always ≥ 1 and grows without bound as v → c. At everyday speeds γ ≈ 1, so relativistic effects are negligible.
- [HL] Time dilation: a moving clock runs slow. The proper time Δt₀ (measured in the clock's own rest frame) relates to the observed time by Δt = γΔt₀. Proper time is always the shortest.
- [HL] Length contraction: a moving object is shortened along its direction of motion. The proper length L₀ (measured in the object's rest frame) relates to the observed length by L = L₀/γ. Proper length is always the longest.
- [HL] The Lorentz transformations relate coordinates between inertial frames: x' = γ(x − vt) and t' = γ(t − vx/c²). They replace the Galilean transformations at high speeds.
- [HL] The invariant spacetime interval (Δs)² = (cΔt)² − (Δx)² has the same value in all inertial frames, even though Δt and Δx individually differ between observers.
- [HL] On a spacetime diagram, ct is plotted on the vertical axis and x on the horizontal. A particle's worldline shows its history; light travels at 45°; the angle of a moving frame's axes increases toward the light line as v increases.