IB Physics SL
Comprehensive flashcards for IB Diploma Physics Standard Level (current guide, first exams 2025). Covers the SL common core across all five themes (A: Space, time and motion; B: Particulate nature of matter; C: Wave behaviour; D: Fields; E: Nuclear and quantum physics) plus Nature of Science and measurement skills.
Ämne: Fysik · Nivå: Gymnasium (16–19) · 458 kort
Innehåll
- Displacement is the straight-line vector from start to finish (magnitude and direction); distance is the total scalar path length travelled.
- Velocity is the rate of change of displacement (a vector); speed is the rate of change of distance (a scalar). SI unit: m s⁻¹.
- Acceleration is the rate of change of velocity: a = Δv/Δt. It is a vector with SI unit m s⁻².
- The four SUVAT equations of motion apply only to uniform (constant) acceleration in a straight line: v = u + at; s = ut + ½at²; v² = u² + 2as; s = ½(u + v)t.
- On a displacement–time graph, the gradient (slope) equals the velocity; on a velocity–time graph, the gradient equals the acceleration and the area under the line equals the displacement.
- Near Earth's surface, the acceleration of free fall (acceleration due to gravity) is g ≈ 9.81 m s⁻², directed downward and independent of the object's mass.
- In projectile motion (ignoring air resistance), the horizontal and vertical components are independent: horizontal velocity is constant and vertical motion has constant acceleration g downward.
- A projectile launched at angle θ with speed u has initial horizontal velocity u·cosθ and initial vertical velocity u·sinθ. The trajectory is a parabola.
- At the highest point of a projectile's path the vertical component of velocity is zero, but the horizontal component (and hence the speed) is non-zero.
- Air resistance on a real projectile reduces its range and maximum height and makes the trajectory asymmetric, with a steeper descent than ascent.
- Newton's first law: an object continues at rest or at constant velocity (in a straight line) unless acted on by a net external force. This defines inertia.
- Newton's second law: the net force equals the 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.
- Weight is the gravitational force on a mass: W = mg. Mass (kg) is a scalar measure of inertia; weight (N) is a force vector that varies with location.
- A free-body diagram shows a single object as a point with all external forces acting on it drawn as labelled arrows. Internal forces and reaction pairs on other bodies are excluded.
- Translational equilibrium occurs when the net (resultant) force on a body is zero; the body is then at rest or moving with constant velocity.
- The normal (contact) force acts perpendicular to a surface. Tension acts along a rope or string, pulling away from the object at each end.
- Hooke's law: for an ideal spring, the restoring force is proportional to the extension, F = kx, where k is the spring constant (N m⁻¹).
- Static friction prevents relative motion and can take any value up to a maximum Fₛ ≤ μₛR. Once sliding begins, dynamic (kinetic) friction acts: F_d = μ_d R, where R is the normal force.
- The coefficient of static friction μₛ is generally greater than the coefficient of dynamic friction μ_d for the same pair of surfaces, so it takes more force to start sliding than to keep sliding.
- Friction always acts to oppose relative motion (or the tendency of relative motion) between two surfaces in contact, parallel to the surface.
- Linear momentum is p = mv, a vector with SI unit kg m s⁻¹. It points in the same direction as the velocity.
- Impulse is the change in momentum: J = Δp = FΔt (for a constant force). On a force–time graph, impulse equals the area under the curve. SI unit: N s (= kg m s⁻¹).
- Conservation of linear momentum: in the absence of external forces, the total momentum of a system is constant. Total momentum before a collision equals total momentum after.
- In an elastic collision, both total momentum and total kinetic energy are conserved. In an inelastic collision, momentum is conserved but kinetic energy is not (some converts to other forms).
- In a perfectly (totally) inelastic collision the colliding bodies stick together and move with a common velocity afterward; this case loses the maximum kinetic energy consistent with momentum conservation.
- Work done by a constant force is W = Fs·cosθ, where θ is the angle between the force and the displacement. SI unit: joule (J = N m). Work is a scalar.
- Kinetic energy of a moving body is E_k = ½mv². It can also be written E_k = p²/(2m) in terms of momentum.
- Change in gravitational potential energy near Earth's surface is ΔE_p = mgΔh, where Δh is the change in height.
- Elastic potential energy stored in a stretched/compressed ideal spring is E_p = ½kx², equal to the area under a force–extension graph.
- Conservation of energy: energy cannot be created or destroyed, only transferred or transformed. The total energy of an isolated system is constant.
- Power is the rate of doing work or transferring energy: P = W/t = E/t. SI unit: watt (W = J s⁻¹). For a force moving at velocity v, P = Fv.
- Efficiency = useful output energy (or power) / total input energy (or power). It is a dimensionless ratio (often given as a percentage) and is always less than 1 for a real device.
- In uniform circular motion the speed is constant but the velocity continuously changes direction, so the body is accelerating. The acceleration (and net force) points toward the centre.
- Centripetal acceleration is a = v²/r = ω²r, directed toward the centre. The centripetal force is F = mv²/r = mω²r.
- Angular velocity ω = Δθ/Δt = 2π/T = 2πf, measured in rad s⁻¹. Linear speed relates to it by v = ωr.
- The centripetal force is not a new kind of force; it is provided by an existing force such as tension, gravity, friction, or the normal force, directed toward the centre.
- Newton's law of gravitation: every point mass attracts every other with a force F = GMm/r², where G = 6.67×10⁻¹¹ N m² kg⁻² and r is the separation of their centres.
- Gravitational force follows an inverse-square law: doubling the separation r reduces the force to one quarter; tripling it reduces the force to one ninth.
- Gravitational field strength g is the gravitational force per unit mass: g = F/m. For a point/spherical mass M, g = GM/r². SI unit: N kg⁻¹ (equivalent to m s⁻²).
- For a satellite in a circular orbit, gravity provides the centripetal force: GMm/r² = mv²/r. This gives orbital speed v = √(GM/r), independent of the satellite's mass.
- Kepler's third law: the square of a planet's orbital period is proportional to the cube of its orbital radius, T² ∝ r³. This follows from combining gravitation with circular motion.
- Temperature is a measure of the average kinetic energy of the particles of a substance. Two objects in thermal contact reach the same temperature at thermal equilibrium.
- The Kelvin and Celsius scales relate by T(K) = θ(°C) + 273. Absolute zero (0 K = −273.15 °C) is the temperature at which particles have minimum kinetic energy.
- Heat (thermal energy) flows spontaneously from a region of higher temperature to one of lower temperature, never the reverse without external work.
- Conduction transfers thermal energy through a material by collisions between particles and (in metals) by free electrons, without bulk movement of the material. Metals are the best conductors because of their delocalised electrons.
- Convection transfers thermal energy through the bulk movement of a fluid (liquid or gas). Heated fluid expands, becomes less dense and rises, while cooler denser fluid sinks, setting up a convection current.
- Thermal radiation is the transfer of energy by electromagnetic waves (mainly infrared) and requires no medium, so it can travel through a vacuum. All bodies above 0 K emit thermal radiation.
- A black, matte surface is the best emitter and best absorber of thermal radiation; a shiny, white or silvered surface is a poor emitter and a good reflector. This is why solar panels are dark and survival blankets are silver.
- Heat (Q) is energy transferred between bodies because of a temperature difference. It is not a property a body 'contains' — a body has internal energy, and heat is energy in transit.