22.2 Aeroscience

22.2.2 Units of measurement. State;

(a) the International System (SI) units for length, mass, time, temperature (K and °C);

Length

• SI Unit: metre (m)

Mass

• SI Unit: kilogram (kg)

Time

• SI Unit: second (s)

Temperature

• SI Unit: kelvin (K)
• Temperature commonly used in aviation: degrees Celsius (°C)

(b) the derivation of the SI units for force, pressure, power, and the non-SI units;

Force

The SI unit for force is the newton (N), derived from:

Force = mass × acceleration

F = ma

• Force is a push or pull that can change an object's motion.

• One newton is the force required to accelerate a mass of 1 kilogram at 1 metre per second squared.

Therefore:

1 N = 1 kg·m/s²

Non-SI unit

• 1 N ≈ 0.225 pounds-force (lbf)

Pressure

The SI unit for pressure is the pascal (Pa), derived from force per unit area.

Pressure = Force / Area

• One pascal is the pressure produced by a force of 1 newton acting over an area of 1 square metre.

Therefore:

1 Pa = 1 N/m²

• 1 hectopascal (hPa) = 100 Pa

• 1013 hPa = 101,300 Pa

• Standard atmospheric pressure is approximately 1013 hPa.

Non-SI units

• 1013 hPa ≈ 14.7 pounds per square inch (psi)

• 1013 hPa ≈ 1.013 bar

• 1013 hPa = 1013 millibars (mb)

Power