Power/weight question...

[Panter]

Fabulous, thanks all

 

[02GF74]

You are lifting YOU and a BIKE against gravity. The energy is the same, or very damned close. It FEELS easier because when you walk up a hill, less fatigued muscle bundles are being used.

No, there is more to it than that. When you walk or run, you lift your CofG up and down at every step and that is a considerable amount of effort.

When you are cycling, sat on yer saddle, your CofG does not go trough the up/down motions so you have more energy to spin the pedals.

I reckon you could keep up with youerself walking or running up a hill on a bike even though you are also carrying the extra weight of a bike with you.

 

[jimboalee]

No, there is more to it than that. When you walk or run, you lift your CofG up and down at every step and that is a considerable amount of effort.

When you are cycling, sat on yer saddle, your CofG does not go trough the up/down motions so you have more energy to spin the pedals.

I reckon you could keep up with youerself walking or running up a hill on a bike even though you are also carrying the extra weight of a bike with you.

Yes, when a person walks, they raise their CoG by about 30mm with every step. That is understood. For me, it accounts for approx 2.6 kCals/min, about half the total calorie spend at 3.12 mph.
Riding my bike at 3.12 mph is not much more than basal metabolic rate of 1.2 kCals/min. ie, sat there doing next to sod all.

Cycling is advantageous in either of two ways. You can either get there at the same speed using a fraction of the energy, or get there sooner using the same or more energy.

It beats me how it took until 1807 AD for man to realise this.

 

[ColinJ]

It beats me how it took until 1807 AD for man to realise this.

Probably because they didn't have bikes (or proper roads) before that!

 

[Yellow Fang]

By my reckoning, the fat guy would be using almost twice as much energy as the thin guy. I could show you my calculations, but I can't be arsed at the moment.

 

[Yellow Fang]

Looking at it, a 30 degree slope is ridiculously steep. It's almost 1 in 2.

 

[darth vadar]

Use PowerCalc on the CTC website.

There are two differences to be considered. 1/ Cross section area, and 2/ Coefficient of Drag.

The cross section area of the big guy wouldn't be double the small guy because a human body consists of a collection of ellyptical solids.
The Cd of the big guy might be LESS than the small guy because his Xsection is NOT double, but his mass IS.

The Cd of the 24 stone vehicle is anybody's guess. We would have to recruit a 22 1/2 stone chap to do some Rolldown tests.

If the two climbed the same hill side by side on the same day, their Joules excertion can be calculated. Mass x gravity x metres rise. This is divided by the time it took them, which is J/s, which is Watts.
Watts for forward motion would be negligable, as the 24 stone vehicle might be doing 2 mph.

I've just done some painting in my living room if you'd like to come and watch it dry ?

 

[screenman]

First both guys are using power going forward, so this needs to be calculated. So using the diopoptheses of ninytopicals solutional bigramiphyc systemilastings I would suggest the bigger man is using only 18.678973% more energy to raise his extra weight.

 

[jimboalee]

Probably because they didn't have bikes (or proper roads) before that!

They didn't have bikes because there were horses to do the pulling, The Lords of the manor would punish any serf who wandered too far.
BUT there were some very fine roads in Britain in 200 AD. I'm amazed the Romans didn't have bicycle Centuries. They had to walk every mile of it.

 

[jimboalee]

I've just done some painting in my living room if you'd like to come and watch it dry ?

This IS the "Technical Section", and as Admin suggested to me in a private mail, 'keep it out of 'Beginners', but go as technical as you like in 'Technical'....That's why its there.'

And as I replied to him "Will do, but there are still some buffoons who read 'technical' threads."

 

[Fiona N]

No, there is more to it than that. When you walk or run, you lift your CofG up and down at every step and that is a considerable amount of effort.

Walking is a fabulous example of continuous exchange of potential and kinetic energy since the potential energy acrued by lifting your body CoG so that it sits atop a straight leg is exchanged for kinetic energy as you lean forwards and your CoG swoops down through the low point - minimum potential energy point - and then you do work to raise it back up onto the straight leg. If you see continuous monitoring of kinetic, potential energy and CoG position they form three braided sin waves - absolutely lovely. Everyone ought to study human movement It has to be said riding a bike may be efficient but it's not nearly so lovely