Library › 11. Physics in karate › Force and pressure
A finger in the ribs hurts. A flat hand with the same force – hardly at all. The difference is called pressure: force divided by area, p = F / A. The unit is the pascal (1 Pa = 1 N/m²); 100,000 Pa equals 1 bar.
Small area, high pressure
Half the area, double the pressure. That simple. That is why karate deliberately uses different striking surfaces (body parts as “weapons”): the punch with the two front knuckles (Seiken), fingertips (Nukite), edge of the hand (Shutō), elbow (Hiji) or palm heel (Teishō). Overview and graphic: Body parts.
| Striking surface | Contact area (example) | Pressure at 1000 N |
|---|---|---|
| Palm heel (Teishō) | approx. 25 cm² | approx. 0.4 MPa (4 bar) |
| Fist, two knuckles (Seiken) | approx. 5 cm² | approx. 2 MPa (20 bar) |
| Middle-finger knuckle (Nakadaka-Ken) | approx. 1 cm² | approx. 10 MPa (100 bar) |
Consequences for training
- Small areas act on a point and penetrate deeply, but demand a conditioned, stably aligned striking surface (Hojo Undō, Makiwara).
- Large areas such as the palm heel spread the force, spare one’s own hand and are suited to shoving away and to targets where a fist is easily injured (e.g. the head).
- Area matters in defence too: a block with the outside of the forearm spreads the force differently from a block with the edge of the hand.
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, Gene Mosca: Physik. Springer, Berlin/Heidelberg, ISBN 978-3-642-54165-0.
- Druck. In: Lexikon der Physik. Spektrum Akademischer Verlag, Heidelberg.