What is an inertial frame of reference?

A reference frame in which a body not acted upon by any net force moves with constant velocity (i.e. Newton's first law holds).

Explain why Newton's first law can be used as a test for whether a reference frame is inertial.

In an inertial frame, a body with no net force acting on it moves with constant velocity. If objects appear to accelerate without any real force, the frame is non-inertial.

What condition must a reference frame satisfy to be classified as inertial?

It must not be accelerating; it is either at rest or moving with constant velocity relative to other inertial frames.

A train moves at constant velocity along a straight track. Is a reference frame attached to the train inertial or non-inertial? Explain.

It is an inertial frame because the train is not accelerating; it moves with constant velocity.

State the first postulate of Einstein's special relativity.

The laws of physics have the same form in all inertial frames of reference.

According to special relativity, would an experiment to determine the laws of electromagnetism give different results in two laboratories moving at different constant velocities?

No, the first postulate states that the laws of physics have the same form in all inertial frames, so both laboratories would obtain identical results.

AQA A-Level Physics 7408

Measurements and Their Errors

Topic overview Use of SI units and their prefixes Limitation of physical measurements Estimation of physical quantities

Particles and Radiation

Topic overview Constituents of the atom Stable and unstable nuclei Particles, antiparticles and photons Particle interactions Classification of particles Quarks and antiquarks Applications of conservation laws The photoelectric effect Collisions of electrons with atoms Energy levels and photon emission Wave-particle duality

Waves

Topic overview Progressive waves Longitudinal and transverse waves Principle of superposition of waves and formation of stationary waves Interference Diffraction Refraction at a plane surface

Mechanics and Materials

Topic overview Scalars and vectors Moments Motion along a straight line Projectile motion Newton's laws of motion Momentum Work, energy and power Conservation of energy Bulk properties of solids The Young modulus

Electricity

Topic overview Basics of electricity Current–voltage characteristics Resistivity Circuits Potential divider Electromotive force and internal resistance

Further Mechanics and Thermal Physics

Topic overview Circular motion Simple harmonic motion (SHM)Simple harmonic systems Forced vibrations and resonance Thermal energy transfer Ideal gases Molecular kinetic theory model

Fields and Their Consequences

Topic overview Fields Newton's law Gravitational field strength Gravitational potential Orbits of planets and satellites Coulomb's law Electric field strength Electric potential Capacitance Parallel plate capacitor Energy stored by a capacitor Capacitor charge and discharge Magnetic flux density Moving charges in a magnetic field Magnetic flux and flux linkage Electromagnetic induction Alternating currents Transformers

Nuclear Physics

Topic overview Rutherford scattering α, β and γ radiation Radioactive decay Nuclear instability Nuclear radius Mass and energy Induced fission Safety aspects

AstrophysicsOptional topic

Topic overview Astronomical telescope consisting of two converging lenses Reflecting telescopes Single dish radio telescopes, I-R, U-V and X-ray telescopes Advantages of large diameter telescopes Classification by luminosity Absolute magnitude, M Classification by temperature, black-body radiation Principles of the use of stellar spectral classes The Hertzsprung-Russell (HR) diagram Supernovae, neutron stars and black holes Doppler effect Hubble's law Quasars Detection of exoplanets

Medical PhysicsOptional topic

Engineering PhysicsOptional topic

Topic overview Concept of moment of inertia Rotational kinetic energy Rotational motion Torque and angular acceleration Angular momentum Work and power First law of thermodynamics Non-flow processes The p–V diagram Engine cycles Second Law and engines Reversed heat engines

Turning Points in PhysicsOptional topic

Topic overview Cathode rays Thermionic emission of electrons Specific charge of the electron Principle of Millikan's determination of the electronic charge, e Newton's corpuscular theory of light Significance of Young's double slits experiment Electromagnetic waves The discovery of photoelectricity Wave–particle duality Electron microscopes The Michelson-Morley experiment Einstein's theory of special relativity Time dilation Length contraction Relativistic mass and energy

ElectronicsOptional topic

Topic overview MOSFET (metal-oxide semiconducting field-effect transistor)Zener diode Photodiode Hall effect sensor Difference between analogue and digital signals LC resonance filters The ideal operational amplifier Inverting amplifier configuration Non-inverting amplifier configuration Summing amplifier configuration Real operational amplifiers Combinational logic Sequential logic Astables Principles of communication systems Transmission media Time-division multiplexing Amplitude (AM) and frequency modulation (FM) techniques

Turning Points in Physics

Einstein's theory of special relativity

2 things to know
Paper 3, section B

Overview

Inertial frames, the two postulates, and the consequences of a constant speed of light.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

What is an inertial frame, and how can Newton's first law test for one?

Key term

What is Einstein's first postulate, and is a train at constant velocity an inertial frame?

Questions from this subtopic

Each one with the model answer underneath.

1
What is an inertial frame of reference?
Model answer
A reference frame in which a body not acted upon by any net force moves with constant velocity (i.e. Newton's first law holds).
2
Explain why Newton's first law can be used as a test for whether a reference frame is inertial.
Model answer
In an inertial frame, a body with no net force acting on it moves with constant velocity. If objects appear to accelerate without any real force, the frame is non-inertial.
3
What condition must a reference frame satisfy to be classified as inertial?
Model answer
It must not be accelerating; it is either at rest or moving with constant velocity relative to other inertial frames.
4
A train moves at constant velocity along a straight track. Is a reference frame attached to the train inertial or non-inertial? Explain.
Model answer
It is an inertial frame because the train is not accelerating; it moves with constant velocity.
5
State the first postulate of Einstein's special relativity.
Model answer
The laws of physics have the same form in all inertial frames of reference.
6
According to special relativity, would an experiment to determine the laws of electromagnetism give different results in two laboratories moving at different constant velocities?
Model answer
No, the first postulate states that the laws of physics have the same form in all inertial frames, so both laboratories would obtain identical results.

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