Sainsbury's nicking petrol off customers?

motorguy

hundredk wrote: »

Stealing your momentum is stealing your fuel - explained here

Only if you werent going to brake to stop at the pumps.

almillar

Think of it this way - these are effectively very flat speed humps that move up and down as you go over them. They increase friction and, if they were on a motorway, would require you to have your foot down a bit harder to maintain the same speed on a level surface.
However, approaching a pump in a petrol station, you are slowing down anyway, so, if they are positioned correctly, they will just replace some of the braking energy you would have had to apply, with friction, helping the car to slow.
The energy you think Sainsburys would steal, was already spent just before you took your foot off the accelerator.

MRab2

Let's be absolutely clear; this devices is absolutely, 100% taking energy from your car. It's not coming from gravity any more than it's coming from the tooth fairy. The question is; is it energy you care about?

In other words, is it energy you'd flare off as heat during braking or will you have to offset the energy taken by generating more from your own petrol tank?

Yes, the energy taken is tiny, but the effects on an individual motorist is irrevelent, only the large scale effect need be discussed. And that's where it gets complicated. In ideal conditions you'd be decelerating to pull up to a pump, but I seriously doubt I'm the only person here who's ever queued to get to a pump, thus in certain circumstances you might actually be accelerating over the plate - in those circumstances the device really is sucking energy straight out your fuel tank.
You might even find yourself parked on it while you wait for a pump to become free etc etc.
Only when all possible circumstances are examined and the norm established can its efficiency be established.
I seriously doubt there's enough information yet for Sainsburys to make any realistic claims about its impact on carbon footprint.

The bottom line is this; when it comes to energy there's no such thing as a free lunch.

molerat

The easy solution is to only install them on natural downhill gradients. Logical installation places would be the downhill slopes of multi storey car parks where you are usually braking all the way down. It would be free energy then.

Money_Grabber13579

molerat wrote: »

The easy solution is to only install them on natural downhill gradients. Logical installation places would be the downhill slopes of multi storey car parks where you are usually braking all the way down. It would be free energy then.

No but some of the people on here apparently want to accelerate down them as well, so they would be stealing their energy too.

Get a life, people!:D

Lemonade_Pockets

MRab2 wrote: »

Let's be absolutely clear; this devices is absolutely, 100% taking energy from your car. It's not coming from gravity any more than it's coming from the tooth fairy.

The bottom line is this; when it comes to energy there's no such thing as a free lunch.

Why don't you and all the other self proclaimed physicists try googling Gravational potential energy.

Dave101t

its not taking extra fuel from your tank than would otherwise be used to roll up to a stop in the 1st place.
unless its a rolling road and expecting you to use your drive to turn the mechanism (which it isnt) then its not costing you a penny.

is standing outside a bakery to keep warm 'costing the bakery more in heating'? dont think so, its already spent energy.

MRab2

Lemonade_Pockets wrote: »

Why don't you and all the other self proclaimed physicists try googling Gravational potential energy.

I don't need to - My Masters degree in Mechanical Engineering taught me quite a bit about potential energy. Like for example; you can't actually extract energy from a potential energy system. Why? Well, you have to expend energy getting it up there in the first place - and thanks to the 2nd law of thermodynamics you expend MORE energy getting it up there than you can ever extract from it on the way down.

If you can work out how to get useable energy from a potential energy system (which would be quite a feat as it doesn't exist as a physical property) then please, let us all know.

AHAR

They've been testing people-powered electricity generation in Japan for a while

Pew_Pew_Pew_Lasers!

!!!!ing hell, there are some tightar3es on here.