Sainsbury's nicking petrol off customers?

MRab2

Lemonade_Pockets wrote: »

Don't disagree with any of that. Just to enlighten me what happens if your taking a walk at beachy head and by accident you walk to far. Your not expending any more energy then you would of been anyway but suddenly your gaining a whole lot more on the way down?? No???

Alternatively if you'd like to explain your theory in more detail i'm happy to learn.

Your problem is you keep looking at only half the system. You have to walk UP beachy head first. If you're a 100kg man, your potential energy at the top will be 162kj (PE = mgh). EXACTLY the same as your kinetic energy when you hit the bottom (KE = .5mv^2).
In energy terms you're neither gaining nor losing energy you're converting potential energy to kinetic energy.

However, none of this is relevent since having looked at the device more closely I don't think potential energy comes into it.

Let me ask you this; ignoring friction if you were to drive over the sainsbury's device; would interacting with it cause your vehicle to
A: Speed up
B: Slow down
C: Remain at a constant speed???

pault123

If time is money then the original poster has spent more money by posting this thread than it would cost to roll over this Eco speed bump! :money: :rotfl:

DrFluffy

bonzer wrote: »

Sainsbury's say this is "green" electricity. What's green about generating electricity from petrol?

So, by that arguement, offsetting isn't green?

freebie-fan-jen

surely if you waste petrol going up this monster ramp you can save energy by rolling off it again?? therefore it wouldnt make a difference at all!!

silly thread lol x

peachyprice

bonzer wrote: »

Sainsbury's are apparently installing a series of plates in the car park in their new Gloucester store that you drive over which powers a generator. This then supplies power to the store.

http://www.guardian.co.uk/environment/2009/jun/15/sainsburys-kinetic-plates-speed-bumps

The claim is this doesn't affect car efficiency. So where's the energy ultimately come from that powers this? So you drive over a raised plate which must very slightly slow your car down, then your engine has to work slightly harder to pick up speed again as a result (i.e. you must use slightly more petrol because it's putting a slight hill in your way).

So isn't this effectively nicking petrol out of your tank to power their store? Isn't this also a really inefficient method of generating electricity?

Levitate over the plates, that'll fool the theiving barstewards :rolleyes:

molerat

ailuro2 wrote: »

You could probably liken it to a dynamo on a bike - you ride the bike and the movement was lighting your bikelamp - but you still cycled along the road and didn't think it was stealing any energy from you.:p

The dynamo creates a load therefore it takes more energy to pedal. Thankyou case proven

mattymoo

On a scale of 1 to 10 how bothered are people that Sainsbury's are "nicking petrol off customers"?

Big fat zero here and I applaud them for their investment in this technology. Supermarkets and their associated distribution chains are huge energy consumers so anything they can do to reduce this has to be for the greater good.

adouglasmhor

Lemonade_Pockets wrote: »

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

As you obviously do not understand it I will attempt to explain. The potential energy of an object is energy that may have been put into it, possibly by raising it up or energy that exists in it naturaly, possibly by being raised up by natural forces. The pads take energy from your car which has been put in by fuel you have bought and paid for. This energy is changed from chemical to thermal (in the combustion chambers of the engine) to kinetic (movement energy) to potential (energy of the gravitational drop). To move off the plate at the same speed you have to burn more fuel (chemical to thermal to kinetic again). I suggest you Google a bit more and post less.

MRab2

mattymoo wrote: »

On a scale of 1 to 10 how bothered are people that Sainsbury's are "nicking petrol off customers"?

Big fat zero here and I applaud them for their investment in this technology. Supermarkets and their associated distribution chains are huge energy consumers so anything they can do to reduce this has to be for the greater good.

You're missing the point. The effect on an individual motorist will be high on zero. Certainly not enough to be noticeable, but since Sainsburys is using this to bolster their green credentials you need to look at the overall effect.

It's hardly a green idea if in order to save themselves 1000kwh off their electricity bill they're *stealing* 2000kwh from motorists.

Lemonade_Pockets

adouglasmhor wrote: »

The pads take energy from your car which has been put in by fuel you have bought and paid for. This energy is changed from chemical to thermal (in the combustion chambers of the engine) to kinetic (movement energy)

Up to this point this is all energy you will have expended anyway in normal driving, pads or no pads.

to potential (energy of the gravitational drop).

This is my bit of the argument, as far as i can see it is this bit that is powering the pads.

To move off the plate at the same speed you have to burn more fuel (chemical to thermal to kinetic again).

If you'd read my previous posts you will have seen that i'm not disagreeing with this. However as previously said if the pads only move down a fraction the extra energy required is nominal maybe even zero if you were slowing down anyway. Where i live the roads are far from smooth so this probably happens 1000's of times on any given journey, one more won't hurt.

So in a effort to articulate my point better. The energy expended before and after the pad would of either been expended anyway or is very negligible. Therefore the only bit that is doing the work is the gravational element in the middle.