Modes of oscillation of tractor aerials

 

The tractor pulling this trailer had two very flexible long radio aerials that showed two modes of oscillation. The first was the waving backwards and forwards from the base, like a tree in the wind. I'd have said the time period was roughly 1 second. The second mode seemed to be the third harmonic - so that there were two discernible nodes dividing the length by three. This would make the frequency 3Hz and thus the time period to be 1/3 of a second. I tried to count oscillations in 10 seconds but it was too quick, suggesting that the estimate for time period is probably correct.