Numford

Properties of matterClass 11, Mechanical Properties of Fluids

Dimensional formula of Surface energy

[M T-2]

SI unitjoule per square metre (J/m²)

Energy per unit area of a liquid surface. Numerically it equals surface tension, and the dimensions match too.

Derivation

How to get the dimensional formula of surface energy

  1. Start from the definition: surface energy = energy / area.
  2. velocity = length / time, so velocity is [L] / [T] = [L T-1].
  3. energy = mass × velocity2, so energy is [M] × [L T-1]2 = [M L2 T-2].
  4. area = length × length, so area is [L] × [L] = [L2].
  5. Put in the dimension of each part: [M L2 T-2] / [L2].
  6. Add the powers of each base quantity: [M T-2].
Same dimensions

Quantities with the dimensions [M T⁻²]

Equal dimensions do not make them the same quantity. Compare surface energy with the others in the full grid.

Practice

Three questions on surface energy

1Which of these has the same dimensions as surface energy?

2What is the SI unit of surface energy?

3Which one has different dimensions from the others?

Questions

Surface energy: quick answers

What is the dimensional formula of surface energy?

The dimensional formula of surface energy is [M T⁻²]. It comes from surface energy = energy / area.

What is the SI unit of surface energy?

The SI unit of surface energy is the joule per square metre (J/m²).

Which quantities have the same dimensions as surface energy?

Surface energy shares [M T⁻²] with spring constant, surface tension. Equal dimensions do not make them the same quantity.

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