Key relationship
Outside: g=GM/r². Inside uniform sphere: g=g₀r/RE; r=RE+h.
Physics · Class 11
Probe gravity inside and above Earth
Above Earth, gravity falls by the inverse-square law. Inside a uniform sphere only the mass enclosed by the probe radius contributes, so gravity decreases linearly to zero at the centre.
Open the interactive experiment →Probe gravity inside and above Earth
புவிக்கு வெளியே ஈர்ப்பு முடுக்கம் 1/r² என குறையும். சீரான அடர்த்தி புவியின் உள்ளே மையத்தில் அது பூஜ்யமாகும்.
Key notes, relationships and model limits
Remember
Above Earth, gravity falls by the inverse-square law. Inside a uniform sphere only the mass enclosed by the probe radius contributes, so gravity decreases linearly to zero at the centre.
Common trap
The exterior inverse-square law cannot be extended unchanged down to the centre.
Model limits
Spherical nonrotating Earth of uniform density inside, inverse-square field outside. Actual Earth is layered and rotating; depth relation is an idealization.
What you will learn
Compare altitude and depth laws and their assumptions.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
At depth RE/2, r=RE/2 and g=g₀/2. At altitude RE, r=2RE and g=g₀/4.
Why this matters
The model connects probe gravity inside and above earth with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
In a uniform Earth, what is gravity at the centre?
- The same as surface gravity
- Zero
- Infinite
Read the explanation
At r=0 the inward contributions cancel and g=g₀r/RE=0.
Course connection: Class XI Chapter 7. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.