4.4.2

Orbits of Planets & Satellites

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Orbital Period and Radius

When an object orbits a more massive body it has a set period and radius which depend on each other.

Orbital period

Orbital period

The time taken for an object to do one full orbit is called the period.
Even if the orbit is elliptical the period will remain constant.

Orbital radius

Orbital radius

The orbital radius is the average distance between the centre of the body and the centre of the object.
For the circle, the radius is always the same.
For an elliptical orbit, the radius changes.

Relationship

Relationship

Orbital period and radius have the following relationship:
- The period squared is proportional to the radius cubed.
- $T^2\; \alpha \; r^3$
The constant of proportionality can be found by finding the gradient of a graph of period squared against radius cubed.
This is Kepler's third law.

Energies of Orbiting Objects

Sometimes, considering the total energy of a system, such as a satellite orbiting a planet, can be much easier than thinking about the resultant force and acceleration of an object.

Circular orbits

Circular orbits

In a circular orbit around a planet, the satellite is always on the same equipotential and so the total energy of an orbiting satellite is constant.
- The planet does no work on the satellites, so there is no loss in potential and no loss in gravitational potential energy (GPE).
- The radius of the orbit does not change.
- The satellite does not change kinetic energy (KE) and so has a constant speed.

Non-circular orbits

Non-circular orbits

This approach also works for non-circular orbits such as ellipses and parabolas.
This is because we can show that the total energy of an orbiting satellite is always equal to half of the gravitational potential energy of the satellite.
This is because gravitational field strength follows an inverse-square law.

1

Space, Time & Motion

1.1

Motion

1.1.1Motion Basics 1.1.2Graphs of Motion 1.1.3Uniform Acceleration Equations 1.1.4Projectile Motion 1.1.5Bouncing Ball Example

1.2

Forces

1.2.1Friction 1.2.2Terminal Speed 1.2.3Newton's Laws 1.2.4Exam-Style Question - Forces 1.2.5End of Topic Test - Newton's Third Law

1.3

Momentum & Impulse

1.3.1Momentum 1.3.2Momentum 2 1.3.3End of Topic Test - Newton's Laws & Momentum

1.4

Work, Energy & Power

1.4.1Work & Energy 1.4.2Conservation of Energy 1.4.3Power & Efficiency 1.4.4IB Multiple Choice- Work, Energy & Power

2

The Particulate Nature of Matter

2.1

Thermal Concepts

2.1.1Molecular Kinetic Theory Model 2.1.2Molecular Kinetic Theory Model 2 2.1.3Thermal Energy Transfer 2.1.4Thermal Energy Transfer Experiments 2.1.5Thermal Equilibrium 2.1.6Thermal Conductivity 2.1.7Heat Energy Transfer

2.2

Modelling a Gas

2.2.1Ideal Gases 2.2.2Ideal Gases 2 2.2.3End of Topic Test - Thermal Energy & Ideal Gases 2.2.4Exam-Style Question - Ideal Gases

3

Wave Behaviour

3.1

Oscillations

3.1.1Progressive Waves 3.1.2Simple Harmonic Motion

3.2

Travelling Waves

3.2.1Wave Speed & Phase Difference 3.2.2Longitudinal & Transverse Waves 3.2.3Electromagnetic Waves 3.2.4Electromagnetic Waves 2 3.2.5Sound Waves

3.3

Wave Characteristics

3.3.1Polarisation

3.4

Wave Behaviour

3.4.1Reflection & Absorption 3.4.2Reflection of Light 3.4.3Refraction 3.4.4Refractive index

3.5

Standing Waves

3.5.1Standing Waves 3.5.2Standing Waves 2 3.5.3End of Topic Test - Standing Waves 3.5.4IB Multiple Choice - Waves

3.6

Simple Harmonic Motion

3.6.1Simple Harmonic Motion 3.6.2Simple Harmonic Systems 3.6.3Energy in Simple Harmonic Motion 3.6.4End of Topic Test - Simple Harmonic Motion 3.6.5End of Topic Test - Simple Harmonic Motion

3.7

Single Slit Diffraction

3.7.1Diffraction

3.8

Interference

3.8.1Interference 3.8.2Interference 2 3.8.3Diffraction Gratings 3.8.4End of Topic Test - Diffraction

3.9

Doppler Effect

3.9.1Doppler Effect

4

Fields

4.1

Circular Motion

4.1.1Circular Motion 4.1.2Centripetal Force 4.1.3IB Multiple Choice - Circular Motion

4.2

Newton's Law of Gravitation

4.2.1Newton's Law 4.2.2Orbits of Planets & Satellites 4.2.3Escape Velocity & Synchronous Orbits 4.2.4End of Topic Test - Gravitational Fields

4.3

Fields

4.3.1Fields 4.3.2Gravitational Field Strength 4.3.3Gravitational Potential 4.3.4Electric Field Strength 4.3.5Electrostatic & Gravitational Forces 4.3.6Electric Potential 4.3.7IB Multiple Choice - Gravitational Fields

4.4

Fields at Work

4.4.1Radial Field Strength 4.4.2Orbits of Planets & Satellites 4.4.3Escape Velocity & Synchronous Orbits 4.4.4End of Topic Test - Gravitational Fields 4.4.5Uniform Electric Fields 4.4.6IB Multiple Choice - Electric Field & Potential

4.5

Electric Fields

4.5.1Electric Charge 4.5.2Conservation of Charge 4.5.3Coulomb's Law 4.5.4Current 4.5.5Potential Difference 4.5.6IB Multiple Choice - Electric Charge

4.6

Magnetic Effect of Electric Currents

4.6.1Magnetism 4.6.2Magnetic Field 4.6.3Magnetic Force 4.6.4Moving Charges in a Magnetic Field 4.6.5IB Multiple Choice - Magnetism

4.7

Heating Effect of Currents

4.7.1Circuits 4.7.2Resistance 4.7.3Power and Conservation 4.7.4IB Multiple Choice - DC Circuits

4.8

Electromagnetic Induction

4.8.1Electromagnetic Induction 4.8.2Electromagnetic Induction 2 4.8.3Magnetic Flux & Flux Linkage 4.8.4End of Topic Test - Electromagnetic Induction

4.9

Power Generation & Transmission

4.9.1Alternating Currents 4.9.2Operation of a Transformer

4.10

Capacitance

4.10.1Capacitance 4.10.2Parallel Plate Capacitor 4.10.3Energy Stored by a Capacitor 4.10.4Capacitor Discharge 4.10.5Capacitor Charge 4.10.6Magnetic Flux Density 4.10.7End of Topic Test - Capacitance & Flux Density

5

Nuclear & Quantum Physics

5.1

Discrete Energy & Radioactivity

5.1.1Atomic Spectra 5.1.2Atomic Structure 5.1.3Photons 5.1.4Discrete Energy Levels 5.1.5Alpha, Beta & Gamma Radiation 5.1.6Scientific Practices - Unstable Nuclei 5.1.7Radioactive Decay 5.1.8IB Multiple Choice - Atomic Physics

5.2

Nuclear Reactions

5.2.1Mass & Energy 5.2.2Nuclear Fission

5.3

The Interaction of Matter with Radiation

5.3.1Particles, Antiparticles & Photons 5.3.2Particle Interactions 5.3.3Classification of Particles 5.3.4Wave-Particle Duality 5.3.5Wave Functions & Probability 5.3.6IB Multiple Choice - Quantum Physics

5.4

Nuclear Physics

5.4.1Nuclear Instability & Radioactive Decay 5.4.2Nuclear Radius 5.4.3IB Multiple Choice - Nuclear Physics

6

Measurements

6.1

Measurements & Errors

6.1.1Fundamental Units 6.1.2SI Prefixes, Standard Form & Converting Units 6.1.3End of Topic Test - Units & Prefixes

6.2

Uncertainties & Errors

6.2.1Limitation of Physical Measurements 6.2.2Uncertainty 6.2.3Estimation 6.2.4End of Topic Test - Measurements & Errors

6.3

Vectors & Scalars

6.3.1Scalars & Vectors 6.3.2Vector Problems

Jump to other topics

1

Space, Time & Motion

1.1

Motion

1.1.1Motion Basics 1.1.2Graphs of Motion 1.1.3Uniform Acceleration Equations 1.1.4Projectile Motion 1.1.5Bouncing Ball Example

1.2

Forces

1.2.1Friction 1.2.2Terminal Speed 1.2.3Newton's Laws 1.2.4Exam-Style Question - Forces 1.2.5End of Topic Test - Newton's Third Law

1.3

Momentum & Impulse

1.3.1Momentum 1.3.2Momentum 2 1.3.3End of Topic Test - Newton's Laws & Momentum

1.4

Work, Energy & Power

1.4.1Work & Energy 1.4.2Conservation of Energy 1.4.3Power & Efficiency 1.4.4IB Multiple Choice- Work, Energy & Power

2

The Particulate Nature of Matter

2.1

Thermal Concepts

2.1.1Molecular Kinetic Theory Model 2.1.2Molecular Kinetic Theory Model 2 2.1.3Thermal Energy Transfer 2.1.4Thermal Energy Transfer Experiments 2.1.5Thermal Equilibrium 2.1.6Thermal Conductivity 2.1.7Heat Energy Transfer

2.2

Modelling a Gas

2.2.1Ideal Gases 2.2.2Ideal Gases 2 2.2.3End of Topic Test - Thermal Energy & Ideal Gases 2.2.4Exam-Style Question - Ideal Gases

3

Wave Behaviour

3.1

Oscillations

3.1.1Progressive Waves 3.1.2Simple Harmonic Motion

3.2

Travelling Waves

3.2.1Wave Speed & Phase Difference 3.2.2Longitudinal & Transverse Waves 3.2.3Electromagnetic Waves 3.2.4Electromagnetic Waves 2 3.2.5Sound Waves

3.3

Wave Characteristics

3.3.1Polarisation

3.4

Wave Behaviour

3.4.1Reflection & Absorption 3.4.2Reflection of Light 3.4.3Refraction 3.4.4Refractive index

3.5

Standing Waves

3.5.1Standing Waves 3.5.2Standing Waves 2 3.5.3End of Topic Test - Standing Waves 3.5.4IB Multiple Choice - Waves

3.6

Simple Harmonic Motion

3.6.1Simple Harmonic Motion 3.6.2Simple Harmonic Systems 3.6.3Energy in Simple Harmonic Motion 3.6.4End of Topic Test - Simple Harmonic Motion 3.6.5End of Topic Test - Simple Harmonic Motion

3.7

Single Slit Diffraction

3.7.1Diffraction

3.8

Interference

3.8.1Interference 3.8.2Interference 2 3.8.3Diffraction Gratings 3.8.4End of Topic Test - Diffraction

3.9

Doppler Effect

3.9.1Doppler Effect

4

Fields

4.1

Circular Motion

4.1.1Circular Motion 4.1.2Centripetal Force 4.1.3IB Multiple Choice - Circular Motion

4.2

Newton's Law of Gravitation

4.2.1Newton's Law 4.2.2Orbits of Planets & Satellites 4.2.3Escape Velocity & Synchronous Orbits 4.2.4End of Topic Test - Gravitational Fields

4.3

Fields

4.3.1Fields 4.3.2Gravitational Field Strength 4.3.3Gravitational Potential 4.3.4Electric Field Strength 4.3.5Electrostatic & Gravitational Forces 4.3.6Electric Potential 4.3.7IB Multiple Choice - Gravitational Fields

4.4

Fields at Work

4.4.1Radial Field Strength 4.4.2Orbits of Planets & Satellites 4.4.3Escape Velocity & Synchronous Orbits 4.4.4End of Topic Test - Gravitational Fields 4.4.5Uniform Electric Fields 4.4.6IB Multiple Choice - Electric Field & Potential

4.5

Electric Fields

4.5.1Electric Charge 4.5.2Conservation of Charge 4.5.3Coulomb's Law 4.5.4Current 4.5.5Potential Difference 4.5.6IB Multiple Choice - Electric Charge

4.6

Magnetic Effect of Electric Currents

4.6.1Magnetism 4.6.2Magnetic Field 4.6.3Magnetic Force 4.6.4Moving Charges in a Magnetic Field 4.6.5IB Multiple Choice - Magnetism

4.7

Heating Effect of Currents

4.7.1Circuits 4.7.2Resistance 4.7.3Power and Conservation 4.7.4IB Multiple Choice - DC Circuits

4.8

Electromagnetic Induction

4.8.1Electromagnetic Induction 4.8.2Electromagnetic Induction 2 4.8.3Magnetic Flux & Flux Linkage 4.8.4End of Topic Test - Electromagnetic Induction

4.9

Power Generation & Transmission

4.9.1Alternating Currents 4.9.2Operation of a Transformer

4.10

Capacitance

4.10.1Capacitance 4.10.2Parallel Plate Capacitor 4.10.3Energy Stored by a Capacitor 4.10.4Capacitor Discharge 4.10.5Capacitor Charge 4.10.6Magnetic Flux Density 4.10.7End of Topic Test - Capacitance & Flux Density

5

Nuclear & Quantum Physics

5.1

Discrete Energy & Radioactivity

5.1.1Atomic Spectra 5.1.2Atomic Structure 5.1.3Photons 5.1.4Discrete Energy Levels 5.1.5Alpha, Beta & Gamma Radiation 5.1.6Scientific Practices - Unstable Nuclei 5.1.7Radioactive Decay 5.1.8IB Multiple Choice - Atomic Physics

5.2

Nuclear Reactions

5.2.1Mass & Energy 5.2.2Nuclear Fission

5.3

The Interaction of Matter with Radiation

5.3.1Particles, Antiparticles & Photons 5.3.2Particle Interactions 5.3.3Classification of Particles 5.3.4Wave-Particle Duality 5.3.5Wave Functions & Probability 5.3.6IB Multiple Choice - Quantum Physics

5.4

Nuclear Physics

5.4.1Nuclear Instability & Radioactive Decay 5.4.2Nuclear Radius 5.4.3IB Multiple Choice - Nuclear Physics

6

Measurements

6.1

Measurements & Errors

6.1.1Fundamental Units 6.1.2SI Prefixes, Standard Form & Converting Units 6.1.3End of Topic Test - Units & Prefixes

6.2

Uncertainties & Errors

6.2.1Limitation of Physical Measurements 6.2.2Uncertainty 6.2.3Estimation 6.2.4End of Topic Test - Measurements & Errors

6.3

Vectors & Scalars

6.3.1Scalars & Vectors 6.3.2Vector Problems

Practice questions on Orbits of Planets & Satellites

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

1
What is the relationship between orbital period and orbital radius of an object?Multiple choice
2
Which statements about orbits are correct?True / false
3
What happens to the period of a planet's orbit when the radius doubles?Multiple choice
4
Select the quantities which do NOT change for a circular orbit:True / false
5
Which of these statements is true for circular orbits?Multiple choice

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Radial Field Strength

Escape Velocity & Synchronous Orbits