Fundamental Forces
-Electromagnetism
-Nuclear Strong
-Nuclear Weak

Newton's Law of Univ. Gravitation: F = G M₁M₂/r²
forces equal in magnitude but oppositely directed

Features:
forces act between mass particles
forces are independent of other bodies

Isostasy = gravitational balancing (Earth's crust responds to force of gravity, i.e., any thickness change in crust causes isostatic adjustment)
Gravimeter used for gravity surveying --- search for gravity anomalies
Earth's shape and rotation
Corrections
-topographic variations (free air corr)
-near surface mass (Bauguer corr)

1. How do gravity anomalies arise? Explain why there is a negative gravity anomaly over mountain chains. How would you expect that the negative gravity anomaly over the Appalachians compares to the negative anomaly over the Rocky Mountains.
2. Gravity readings taken on the Earth's surface must be corrected before a gravity anomaly can be detected. Identify and briefly describe two such corrections.
3. Draw a labeled cross-section through an elevated mountain chain and an adjacent continental margin and show how the area responds isostatically to weathering of the mountains.

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