Edexcel iGCSE Physics - 8.1 Astrophysics Units- Study Notes- New Syllabus
Edexcel iGCSE Physics -8.1 Astrophysics Units- Study Notes- New syllabus
Edexcel iGCSE Physics -8.1 Astrophysics Units- Study Notes -Edexcel iGCSE Physics – per latest Syllabus.
Key Concepts:
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8.1 Astrophysics – Units
In astrophysics, physical quantities must be measured using correct SI units. Using the correct unit is essential in calculations, graphs, and exam answers.
Key Statement
Statement: Astrophysics calculations use the SI units kilogram (kg), metre (m), second (s), metre per second (m/s), metre per second squared (m/s²), newton (N), and newton per kilogram (N/kg).
Base Units Used in Astrophysics
| Quantity | Unit | Symbol |
|---|---|---|
| Mass | kilogram | kg |
| Distance / radius | metre | m |
| Time | second | s |
Derived Units Used in Astrophysics
| Quantity | Unit | Symbol |
|---|---|---|
| Speed / velocity | metre per second | m/s |
| Acceleration | metre per second squared | m/s² |
| Force | newton | N |
| Gravitational field strength | newton per kilogram | N/kg |
Meaning of Important Units
- m/s → how fast an object is moving.
- m/s² → how quickly velocity changes.
- N → force acting on an object.
- N/kg → force per unit mass (gravitational field strength).
Key idea: Gravitational field strength tells us how strong gravity is at a point.
Common Astrophysics Relationships and Units
- Force → measured in newtons (N).
- Mass → measured in kilograms (kg).
- Acceleration due to gravity → measured in m/s² or N/kg.
\( \mathrm{1\ N/kg = 1\ m/s^2} \)
Important: Gravitational field strength can be expressed in either unit.
Exam Tips
- Always include correct units in answers.
- Convert quantities into SI units before calculation.
- Check squared units carefully (m/s²).
Summary
- Astrophysics uses SI units.
- Mass is measured in kg and distance in m.
- Speed is measured in m/s and acceleration in m/s².
- Force is measured in N and gravitational field strength in N/kg.
Example
A spacecraft accelerates at 2.5 m/s². State the SI unit of acceleration and explain what this value means.
▶️ Answer / Explanation
- The SI unit of acceleration is m/s².
- The velocity increases by 2.5 m/s every second.
Example
The gravitational field strength on a planet is 12 N/kg. Explain what this value means.
▶️ Answer / Explanation
- Each kilogram of mass experiences a force of 12 N.
- This is the strength of the planet’s gravitational field.