Wikipedia. And it's exactly the same equation for drag in every textbook on aerodynamics.Chris Jeggo wrote: ↑13 Nov 2022, 10:30pm Jonathan, please quote the source of your two screenshot equations.
Jonathan
Wikipedia. And it's exactly the same equation for drag in every textbook on aerodynamics.Chris Jeggo wrote: ↑13 Nov 2022, 10:30pm Jonathan, please quote the source of your two screenshot equations.
Save me some time please. Wikipedia URL?Jdsk wrote: ↑13 Nov 2022, 10:32pmWikipedia. And it's exactly the same equation for drag in every textbook on aerodynamics.Chris Jeggo wrote: ↑13 Nov 2022, 10:30pm Jonathan, please quote the source of your two screenshot equations.
Jonathan
The power to push the the air past an anchored object comes from the wind. (You can gather it with a turbine and generate electricity.)Chris Jeggo wrote: ↑13 Nov 2022, 10:35pm Suppose a tricyclist is just sitting, relaxing, on a trike which is nailed to the road in a headwind. Where does your power come from?
Drag (physics)Chris Jeggo wrote: ↑13 Nov 2022, 10:38pmSave me some time please. Wikipedia URL?Jdsk wrote: ↑13 Nov 2022, 10:32pmWikipedia. And it's exactly the same equation for drag in every textbook on aerodynamics.Chris Jeggo wrote: ↑13 Nov 2022, 10:30pm Jonathan, please quote the source of your two screenshot equations.
I don’t think so.Case (2): Stationary trike in headwind - cyclist stops trike rolling backwards by pressing down on forward pedal. Cyclist does no work because pedal is not moving downwards - no work, no power.
Yes, sure, we can lash ourselves to the mast, or nail our trike to the road. We agree.Nearholmer wrote: ↑13 Nov 2022, 11:01pmI don’t think so.Case (2): Stationary trike in headwind - cyclist stops trike rolling backwards by pressing down on forward pedal. Cyclist does no work because pedal is not moving downwards - no work, no power.
We all know that it takes effort, consumes energy, to remain stationary in a decently strong wind, but we aren’t moving, so no work, right?
Wrong. We are making multiple tiny movements, bracing ourselves against the buffeting, constantly slightly over compensating and moving forward, relaxing slightly and moving backward, and repeating that cycle.
The better braced we are, the less each little power-blip will be, but unless we lash ourselves to the mast and relax, I’m sure we’ll output power, use energy, and get tired.
That can be the case. But consider the case where a stake anchors the trike to the ground. Just like a building. No power source in either. Then the power to push the air past the object comes from the wind.Nearholmer wrote: ↑13 Nov 2022, 11:01pmI don’t think so.Case (2): Stationary trike in headwind - cyclist stops trike rolling backwards by pressing down on forward pedal. Cyclist does no work because pedal is not moving downwards - no work, no power.
We all know that it takes effort, consumes energy, to remain stationary in a decently strong wind, but we aren’t moving, so no work, right?
Wrong. We are making multiple tiny movements, bracing ourselves against the buffeting, constantly slightly over compensating and moving forward, relaxing slightly and moving backward, and repeating that cycle.
The better braced we are, the less each little power-blip will be, but unless we lash ourselves to the mast and relax, I’m sure we’ll output power, use energy, and get tired.
Just remaining seated on the trike, even if it’s nailed to the road, we will be going through the same micro-cycles of force and distance holding our bodies upright against the wind. To do no work, not to go through those bracing cycles, we have to relax, in which case we will instantly get blown off the trike.Yes, sure, we can lash ourselves to the mast, or nail our trike to the road. We agree.
If it's a recumbent trike you could fall asleep on it.Nearholmer wrote: ↑13 Nov 2022, 11:16pmJust remaining seated on the trike, even if it’s nailed to the road, we will be going through the same micro-cycles of force and distance holding our bodies upright against the wind. To do no work, not to go through those bracing cycles, we have to relax, in which case we will instantly get blown off the trike.Yes, sure, we can lash ourselves to the mast, or nail our trike to the road. We agree.
If it’s windy where you are, go outside and try standing stock still. It’s tiring, more tiring than standing still when there is no wind, and it’s tiring because you are doing extra work, not by making gross movement like walking, but through millions of tiny movements.
I missed this bit. With or without the elastic cycle the energy to push the air past the object eventually comes from the wind, as you say. It doesn't require a power source in the trike or tree or building.Nearholmer wrote: ↑13 Nov 2022, 11:01pm ...
Trees and flag poles don’t I think expend energy standing up in a gale, they receive it from the wind, store it by bending elastically, and when the wind abates for a moment give up most of it by pinging back to their normal position, displacing air in so doing. They presumably warm-up a bit in the process. If their elastic limit is exceeded they snap.
Yes, another type of anchored object in a moving fluid.Nearholmer wrote: ↑13 Nov 2022, 11:22pmYes, on a recumbent you could relax and have a Kip in a gale, in which case (assuming the brakes are good), you and the bike become like the tree or the flag pole.