IB Physics IA idea · Space and astronomy data
IB Physics IA idea: test Kepler's third law with real satellite data
Hundreds of satellites share one law. Use their public orbital data to test it and weigh the Earth.
These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.
Example research question
How does the square of orbital period depend on the cube of orbital radius, from 6,800 km to 42,200 km, for 12 near-circular satellites with public two-line element sets, and what mass of the Earth follows?
Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Physics IA guide.
Variables
- You change
- orbital radius, 6,800 to 42,200 km for 10 or more satellites
- You measure
- orbital period, 90 to 1,436 minutes
- You keep the same
- same central body
- data epoch
- elliptical versus circular
- source of data
Method
Download two-line element sets for satellites at various altitudes (ISS, Starlink, GPS, geostationary) and compute period and semi-major axis. Choose near-circular orbits.
Data analysis
Plot T^2 against a^3; the gradient gives 4 pi^2/(G M_earth). Compare M_earth with the accepted value; include the effect of eccentricity as a systematic error.
How it works
You change Orbital radius cubed (km³) and measure Orbital period squared (min²) in Earth satellites, keeping Near-circular orbits, Data source, Epoch of data the same. Expect a graph of T² / min² against a³ / km³: The gradient gives 4π²/(GM_Earth).
Make it yours
Add Molniya or other highly elliptical orbits and test the semi-major-axis form.
Extended Essay angle
Include J2 precession and atmospheric drag decay of the orbit.
Safety
None.
Data sources
More Physics IA ideas in Space and astronomy data
- Planet shadows: do transit depths match the published radii?In the Photon IA Guide
A planet crossing its star dims it by a tiny amount. Check that the dip you measure matches the size the catalogue claims.
- Kepler's third law beyond the Sun: can orbits weigh distant stars?Free with an account
Planets around other stars follow the same law as ours. Their orbits reveal the star's mass.
- Weighing planets: can moon orbits give Jupiter's mass?Free with an account
A planet's moons orbit under its gravity, so their periods reveal its mass.
- Star cluster in Gaia: how far away is it?In the Photon IA Guide
A cluster's stars lie on a clean main sequence. Compare its distance from parallax and from fitting the sequence.
- Two ways to measure the expansion rate: why do they disagree?In the Photon IA Guide
The universe's expansion rate comes out different when measured from nearby supernovae and from the early cosmic microwave background.
- Listening to a black-hole merger: can you recover the masses?In the Photon IA Guide
The first gravitational wave rose in pitch as two black holes spiralled in. Its chirp encodes the masses.
- Numerical orbits: which integrator can you trust for 1,000 years?In the Photon IA Guide
Simple methods quietly gain or lose energy as a planet orbits. Measure how fast, and which methods avoid it.
- Do bigger stars really shine as M^3.5? Test it with binary stars.In the Photon IA Guide
Eclipsing binaries give the most accurate stellar masses and radii. Use them to test how luminosity scales with mass.
Other free Physics IA ideas
- Damped pendulum: which drag law fits the swing?
- Where you pluck matters: how do the harmonics change?
- Pencil traces: how well does graphite conduct?
- Metal wire: how much does its resistance rise with temperature?
- A CD as a grating: can you measure the width of its tracks?
- Rubber band: how much energy does a stretch cycle lose?
- Ball in syrup: how does terminal speed depend on size?
- Metal rod: how much does it grow when it is heated?
- Small wind turbine: does power rise as the cube of the wind speed?
- Transformers: how close to ideal is the turns ratio?
- Salt substitute: can you detect natural radioactivity in food?