Measuring wave forces

The weather kept us on land today, which gave us a chance to catch up on some unexciting but necessary work.

We're very interested in the forces that waves exert when they hit the shore. Strong waves can tear large chunks out of the mussel bed. It's one example of ecological disturbance, where organisms are killed, injured, or removed from the ecosystem (in our case, they are ripped of the rocks). Forest fires are another type of ecological disturbance.

To measure the maximum wave force, we use some clever, simple devices call "dynamometers" or "drogues" (I usually call them dynos). Basically, we attach a whiffle ball to a spring that is, in turn, attached to a string. When waves pull on the ball, the spring lengthens, and a small rubber stopper moves down the string. By measuring how far the stopper moves and doing a little math, we can approximate the maximum drag force that the ball has experienced since the previous reading. In the field, we usually check the dynamometers once a day. The Denny Lab at Stanford has an excellent page on making and using dynamometers.

Before you can put the dynos in the field and start measuring waves, they need to be calibrated to find their spring constant. For this, we hang a range of weights from the dyno and measure how far the stopper moves.

Jenny demonstrates her stopper measurement technique

Multiplying the weight by the acceleration of gravity gives us the force exerted on the spring by the weight. Then we plot the force of a range of weights against the movement of the stopper and derive the spring constant. Now repeat eleven million times to calibrate all the dynos. It's THRILLING.

Gary wants to calibrate dynamometers all day, every day

OK, it's not the most exciting part of research. But it needs to be done, and working together helps it go quickly. Plus, you can always treat yourself for your hard work.

Nachos!

Hoping for calmer weather tomorrow.