Sainsbury's nicking petrol off customers?

mikey72

DaisyClaire wrote: »

For petes sake you don't get kinetic energy from petrol! [slaps forehead]

Kinetic energy is down to the motion; ie: the extra energy generated from movement.

We possess kinetic energy simply by walking, running etc. Gravity is the force which keeps us 'stuck to the ground' kinetic energy is the energy created as we move, friction.

If sainsburys want your petrol that badly I would personally find a syphon more effective!

My car doesn't doesn't move much without petrol. But the brakes convert the kinetic energy from the petrol to heat, through friction though, to slow me down. The plate will convert my kinetic energy it to electricity, instead of braking, but it's still not green, as my petrol will then be used to restore my kinetic energy, to beat another customer into a parking space.

Lemonade_Pockets

Most of you have completely misread the situation.

It does not take the kinetic energy from the car. This would only be possible if the plate moved fore and aft (laterally). Think jumping onto a skate board mid run. The heat from brakes has nothing to do with it either.

You drive over the pad. The cars weight (gravity) causes the plate to be pushed down into the ground. This gives the plate kinetic energy as it moves down and then presumably rebounds off some sort of spring to return to its original position. It is this kinetic energy that is then used to generate the power.

pelirocco

Lemonade_Pockets wrote: »

Most of you have completely misread the situation.

It does not take the kinetic energy from the car. This would only be possible if the plate moved fore and aft (laterally). Think jumping onto a skate board mid run. The heat from brakes has nothing to do with it either.

You drive over the pad. The cars weight (gravity) causes the plate to be pushed down into the ground. This gives the plate kinetic energy as it moves down and then presumably rebounds off some sort of spring to return to its original position. It is this kinetic energy that is then used to generate the power.

Surely not ? that could never happen on here :rolleyes:

mikey72

Lemonade_Pockets wrote: »

Most of you have completely misread the situation.

It does not take the kinetic energy from the car. This would only be possible if the plate moved fore and aft (laterally). Think jumping onto a skate board mid run. The heat from brakes has nothing to do with it either.

You drive over the pad. The cars weight (gravity) causes the plate to be pushed down into the ground. This gives the plate kinetic energy as it moves down and then presumably rebounds off some sort of spring to return to its original position. It is this kinetic energy that is then used to generate the power.

Er no, but I love the idea of the big springs under the plates.
More to the point, as has already been quoted from the manufacturer's website

" the ramp at this point scavenges a degree of kinetic energy as the car passes over it, but this is far less than is lost through other mechanisms. "

hundredk

Bongedone wrote: »

Anyhow, if it is taking the power from the cars momentum you should really be slowing down at the point in the picture anyway.

Stealing your momentum is stealing your fuel - explained here

motorguy

bonzer wrote: »

Er no. All the energy is coming from your car petrol tank. When you come down a hill you're under gravity. What gets you up a hill in the first place? - petrol. When you go down into a dip (gravity). Come out of the dip (petrol).

There's no magical free energy. It's electricity generated from a petrol engine by a convoluted method.

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

I would suggest its using the energy that you would otherwise lose from braking at the pump where it would be lost as heat into the discs / pads

Unless of course you time your freewheeling from when you enter the filling station to stop you exactly right beside the pump each time, then under those circumstances it would probably stop you a metre short, but here in the real world i dont think its going to be an issue.

Lemonade_Pockets

mikey72 wrote: »

" the ramp at this point scavenges a degree of kinetic energy as the car passes over it, but this is far less than is lost through other mechanisms. "

Maybe you should try reading it in context.

mikey72

I must admit, I don't really care for the amount it will take from me personally, but I can't see how it's green to burn hydrocarbons to move a car, with all it’s losses, then run it over the equivalent of a wave machine, with further losses, to turn the momentum to electricity.
More economical just to burn it in a power station in the first place

Lemonade_Pockets

http://www.guardian.co.uk/environment/2009/feb/08/alternative-energy-speed-bumps

It doesn't help when journo's missuse words but the idea is explained here.

The kinetic energy in question as previously stated is purely the pad moving up and down in a horizontal plane. This up and down movement is a direct result of the cars weight pushing it down then it springing back up when the car moves off it.

Infact you would probably got more from the pad if you accelerated over the pad at 100mph as it would compress and unweight faster!!!

prowla

DaisyClaire wrote: »

For petes sake you don't get kinetic energy from petrol! [slaps forehead]

Kinetic energy is down to the motion; ie: the extra energy generated from movement.

We possess kinetic energy simply by walking, running etc. Gravity is the force which keeps us 'stuck to the ground' kinetic energy is the energy created as we move, friction.

If sainsburys want your petrol that badly I would personally find a syphon more effective!

The kinetic energy in a car is produced as a result of the car moving. The car moves because of the engine, which uses petrol.
You cannot seriously think that the motion of a car comes from nowhere?!?!?

Bongedone wrote: »

From the manufactures website it is meant to replace breaking. As another poster said above. It replaces heat that would be generated by using the breaks.

Dude - it's braking (not breaking).

Lemonade_Pockets wrote: »

Most of you have completely misread the situation.

It does not take the kinetic energy from the car. This would only be possible if the plate moved fore and aft (laterally). Think jumping onto a skate board mid run. The heat from brakes has nothing to do with it either.

You drive over the pad. The cars weight (gravity) causes the plate to be pushed down into the ground. This gives the plate kinetic energy as it moves down and then presumably rebounds off some sort of spring to return to its original position. It is this kinetic energy that is then used to generate the power.

If your car presses down on the pad, then either (a) the pad is raised above the road surface so the car has to climb on to it, or (b) it sinks into the road under the weight of the car so that the car has to climb out of the hole. It may be only a centimeter movement either way, but the energy comes from the car, and thus from the fuel burned.
The only way it could be free was if you were freewheeling to the point of energy capture and you did not need to accelerate again after it.