Platform video: How to Use The Prowler

[convergentsum]

My guess is that the benefit of greater velocity / momentum is that it helps overcome macroscopic bumps and whatnot that would otherwise demand extra force or slow you down back into stiction territory.

[Joe Wilson]

My understanding of kinetic friction force is that it is solely a function of normal force and coefficient of kinetic friction neither of which are functions of speed. Given that, I always thought the idea that prowler work is easier when you push it faster is simply a perception thing. Obviously, when you stop, the force required to overcome the static friction will be higher than if you just keep pushing, but after movement is started, the force required to keep pushing should be the same.

Do you have an alternate explanation (other than perception) to explain why prowler work seems to be easier when you push faster?

I can't think of a physical reason for why a prowler would require discernibly less force to push at higher speeds. The kinetic friction coefficient does have some speed dependence at very low speeds, i.e. the transition from static friction to kinetic friction is smooth/continuous rather than an abrupt jump. However, I suspect the speed range over which this transition occurs is so small that one wouldn't actually be able to continuously operate the prowler within it and thus for practical purposes would be an abrupt jump.

If anything I would expect the required force to increase at higher speeds as drag force (air resistance) is proportional to the square of the relative fluid velocity, however, this effect is probably small enough that it again wouldn't actually be discernible to the person operating the prowler.

[Matthew_888]

I can't think of a physical reason for why a prowler would require discernibly less force to push at higher speeds. The kinetic friction coefficient does have some speed dependence at very low speeds, i.e. the transition from static friction to kinetic friction is smooth/continuous rather than an abrupt jump. However, I suspect the speed range over which this transition occurs is so small that one wouldn't actually be able to continuously operate the prowler within it and thus for practical purposes would be an abrupt jump.

If anything I would expect the required force to increase at higher speeds as drag force (air resistance) is proportional to the square of the relative fluid velocity, however, this effect is probably small enough that it again wouldn't actually be discernible to the person operating the prowler.

Please, use the Internet... test your expectations.

https://www.khanacademy.org/science/...iction-example

[Itchysoles]

Please, use the Internet... test your expectations.

Yep, and there is evidence in the article linked a couple times earlier in this thread of kinetic friction coefficient changing within speeds that a sled would be pushed at.

[Joe Wilson]

Thanks, I missed that link. I'll give it a read.

[convergentsum]

It occurs to me that measurement would be most welcome, not just to settle this issue re the science of friction, but also for programming the exercise, esp. if you end up using different prowlers on different surfaces. How hard would it be to fit some kind of meter to the handles?

[Mark Rippetoe]

It's just not necessary, guys. It's a conditioning tool. Just use it as has already been described.

[AndrewLewis]

I can't think of a physical reason for why a prowler would require discernibly less force to push at higher speeds. The kinetic friction coefficient does have some speed dependence at very low speeds, i.e. the transition from static friction to kinetic friction is smooth/continuous rather than an abrupt jump. However, I suspect the speed range over which this transition occurs is so small that one wouldn't actually be able to continuously operate the prowler within it and thus for practical purposes would be an abrupt jump.

If anything I would expect the required force to increase at higher speeds as drag force (air resistance) is proportional to the square of the relative fluid velocity, however, this effect is probably small enough that it again wouldn't actually be discernible to the person operating the prowler.

I very much doubt that air resistant variation at these speeds are going to be anything more than negligible. If you really want to get that deep, you'd have to start looking at the boundary layer where the fluid flow goes from laminar to turbulent, but as Rip says: who cares? Just push the damn thing.

I was just curious about the observation that the sled "hangs on" at slower speeds.

[AndrewLewis]

It occurs to me that measurement would be most welcome, not just to settle this issue re the science of friction, but also for programming the exercise, esp. if you end up using different prowlers on different surfaces. How hard would it be to fit some kind of meter to the handles?

Not very hard. You could outfit an Arduino and force meter to an intermediary between the upright poles and the person's hands. When I was an undergrad, I got into a quantitative analysis of cleans and snatches with video analysis and Matlab, but it turns out, you'd be better putting your time and money into something else like coaching and milk.

[Greg Ruhl]

Video

Prowler issue - YouTube

This is showing it unloaded so it's exacerbating the problem. I'm trying to push forward/down. You can see it moves when I drop my COM and stops when I raise it at the end.

I'll do 100ft pushes with 90# added on this driveway. For comparison I'll do 180# added on astroturf (with a different sled).