# Surface Area

1. May 13, 2004

### Chrono

Taking martial arts they use a bit of physics to try to explain why we do certain things. Our instructor will tell us to manipulate our hands or feet so that we hit the target with less surface area. I understand the concept that the less surface area you hit with the more powerful it will be, since energy is concentrated. I was just wondering if my understanding is correct, and if it is, can anyone kind of expand on it?

2. May 13, 2004

### enigma

Staff Emeritus
Stress is what causes a material to fail, not force. Stress is force divided by area. The larger the area, the larger the force needed to cause it to fail. The smaller the area, the smaller the force needed.

That's why pyramids get bigger at the bottom. There is a larger force because it has the weight of all the bricks above it pushing through, but the larger area keeps it from crumbling.

3. May 15, 2004

### pallidin

Take a hammer and lightly strike a board. Note the minimal depression created.
Then, glue a BB to the center of the head of the hammer, and strike the board with the same force as before.
The attached BB will create a depression depth far greater than the depth created from a bare hammer. Of course, this is due to the fact that the reduced contact area of the BB transmits the entire force of the hammer and motion to a much smaller area of the board.
This can be important in martial arts, as "pressure points" located throughout the body are attacked. These points are not "wide", and so a blow to that area is to be ideally concentrated on that point for maximum effect on that nerve.

4. May 15, 2004

### Chrono

I see. Good analogy, it helped to understand better.