Altimeter
Explore the relationship between atmospheric pressure and altitude
Author:
Title 4
Learning objectives :
This experiment allows students to understand the relationship between atmospheric pressure and altitude. It develops the ability to establish mathematical models from experimental data.
Concepts covered
Atmospheric pressure, Relationship between pressure and altitude, Mathematical modeling, Terrestrial atmosphere, Calibration of measuring instruments
What students will do :
The student uses the FizziQ atmospheric pressure sensor to take measurements at different heights, such as the floors of a building or on a hill. For each level, it records the pressure and estimated altitude, then analyzes the relationship between these values to determine how pressure decreases with altitude. From this data, the student develops a formula to calculate altitude from pressure.
What is required :
Smartphone with FizziQ (iPhone or Android with external sensor), Access to a multi-storey building or a hill, Tape measure, Experience book
Scientific background :
Atmospheric pressure decreases with altitude in an approximately exponential relationship. At sea level, the standard pressure is about 1013.25 hPa, but it decreases by about 1 hPa every 8.5 meters at low altitudes. This relationship is not perfectly linear over large variations in altitude, because air is compressible and its density also decreases with altitude. For small altitude variations (a few hundred meters), we can use the simplified barometric approximation: Δh ≈ (P₀ - P) × 8.5, where Δh is the altitude difference (in meters), P₀ the pressure at the reference point and P the pressure at the measurement point (in hPa). For more precise calculations over large amplitudes, the complete barometric formula takes temperature into account. Modern smartphones incorporate precision barometers (±0.1 hPa, equivalent to approximately ±1 meter of altitude) to improve GPS positioning and other functions.