Study Guides/Physics/Dimension of G (Gravitational Constant)
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What is the Dimensional Formula of Gravitational Constant (G)?

In physics, the capital letter 'G' stands for the Universal Gravitational Constant. This is a massive, unchanging number that dictates the strength of gravity across the entire universe, pulling planets and stars together.

The dimensional formula of the Universal Gravitational Constant (G) is [M⁻¹ L³ T⁻²].

Question (Click to Flip)

What is the dimensional formula of the universal gravitational constant?

Answer

The dimensional formula for capital G is [M⁻¹ L³ T⁻²].

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Key Facts

Quantity: Universal Gravitational Constant (Capital 'G').

Formula Used: Newton's Law of Gravitation [F = G(m1m2)/r²].

Dimensional Formula: [M⁻¹ L³ T⁻²].

SI Unit: N·m²/kg².

Universal Value: The value of G is exactly 6.674 Ɨ 10⁻¹¹ NĀ·m²/kg² everywhere in the universe.

Step-by-Step Derivation

We cannot guess the dimension of G. We must derive it mathematically using Newton's Universal Law of Gravitation. The formula states the force (F) between two masses (m1 and m2) separated by a distance (r) is:

F = G (m1 Ɨ m2) / r²

Step 1: Rearrange the formula to isolate 'G' on one side: G = (F Ɨ r²) / (m1 Ɨ m2)

Substituting the Base Dimensions

Step 2: Substitute the known dimensions of Force, Distance, and Mass into the equation.

  • Dimension of Force (F) = [M¹ L¹ T⁻²]
  • Dimension of Distance squared (r²) = [L²]
  • Dimension of Mass Ɨ Mass (m1 Ɨ m2) = [M²]

Step 3: Put them into the rearranged formula: G = ( [M¹ L¹ T⁻²] Ɨ [L²] ) / [M²]

Step 4: Simplify the equation using basic algebra (laws of exponents):

  • For Mass (M): 1 - 2 = -1
  • For Length (L): 1 + 2 = 3
  • For Time (T): remains -2

Final Dimension of G = [M⁻¹ L³ T⁻²].

Deriving the SI Unit

Using the formula G = (F Ɨ r²) / (m1 Ɨ m2), we can also find the SI unit without memorizing it:

  • F is in Newtons (N)
  • r² is in meters squared (m²)
  • m1Ɨm2 is in kilograms squared (kg²) Therefore, the SI unit of G is NĀ·m²/kg².

Questions and Answers

What is the dimensional formula of the universal gravitational constant?+

The dimensional formula for capital G is [M⁻¹ L³ T⁻²].

How do you derive the dimension of G?+

You rearrange Newton's Law of Gravitation to G = (F Ɨ r²) / (m1 Ɨ m2). Then, you plug in the dimensions for force [MLT⁻²], distance [L²], and mass [M²] and simplify.

Is capital G the same as small g?+

No. Capital G is a universal constant with dimension [M⁻¹ L³ T⁻²]. Small g is acceleration due to gravity with dimension [M⁰ L¹ T⁻²].

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