Energy and work

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Fast hits hard. Kinetic energy is E = ½ · m · v² (unit: joule) – and speed is squared. Twice as fast: four times the energy. Twice as heavy: only twice the energy. Staying loose pays off.

Work is force times distance, W = F · s. A long run-up, lots of energy. But: at close range there is no long run-up. There, what counts is what builds up over a few centimetres.

Worked example

  • 2 kg at 8 m/s: E = ½ · 2 kg · (8 m/s)² = 64 J
  • 2 kg at 10 m/s: E = ½ · 2 kg · (10 m/s)² = 100 J
  • 4 kg at 8 m/s: E = ½ · 4 kg · (8 m/s)² = 128 J

Where the energy goes

On impact, kinetic energy is converted: into movement of the target (displacement), into deformation and heat in the tissue and – unwanted – into one’s own joints giving way. A strike with a short contact time converts a large part of the energy in the target; a push converts it rather into movement of the whole body (see Momentum and impulse).

Connection to training

  • Speed is the biggest lever for energy; it comes from relaxed movement, not from tense strength.
  • Mass contributes through body commitment: hips, trunk and stance transmit it.
  • Short techniques (e.g. in Sanchin or in Kake-Te) make up for the short acceleration path through body structure and whole-body movement.

All calculated values: simplified examples, not measurements. The body is not a rigid block – real values depend heavily on technique, target and measuring method.

Sources

  • Paul A. Tipler: Physik. Spektrum Akademischer Verlag, Heidelberg/Berlin 1994, ISBN 3-86025-122-8.
  • Wolfgang Nolting: Grundkurs Theoretische Physik 1: Klassische Mechanik. 8. Aufl., Springer, Berlin 2008, ISBN 978-3-540-34832-0.

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