[thedoc (OP)]

To keep fit, I deliver weekend newspapers. So I've got a trolley for doing that. The trolley in question has got no suspension, but it does have fairly broad wheels to take a load.  Now, I've noticed that when the trolley is empty, if I'm putting it along the path, it's actually extremely noisy.  It rattles a lot.  But if I pull it along the verge adjacent to the path, which is not particularly smooth, but it is at least grassy, the noise drops by probably 20 to 30 decibels.  Any idea why, considering the surface really should be considered to be a bit rougher than the surface so that's supposedly smoother than the path itself?
Asked by Peter


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[chapter podcast=1000585 track=14.01.07/Naked_Scientists_Show_14.01.07_1001823.mp3]  ...or Listen to the Answer[/chapter] or [download as MP3]