Amp-hours calculation

JohnD is clearly ill equipped to contribute

*/snip/*

He just doesn't get it.

I think you may have meant GarethH there, but your point still stands.

Energy always has a time component, irrespective of whether the units you are using and manipulating are masking it or not.

Dimensionally, energy is always expressed as M L^2 T^-2 *, whatever units are used. Just because some units may not appear to be related to time doesn't mean that time is not implicit to those units.

So...

Energy is not related to time.

No. It most indeedly is.


* M = mass; L = length; T = time.
 
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Energy has no time.
A Joule is one Neutron at a height of one meter.

Power however does have time.
So a Joule per second is a Watt.

I do think it is easy to get Energy and Power mixed up. This is not helped when units like kWh are used for Energy you see the h for hour and think there is some time component.

At 63 I used both Imperial and Metric in my time and it would seem we did not simply swap units but also methods to measure at the same time.

With Imperial we had the Poundal which would give a pound an acceleration of one foot/second and the pound would give a slug an acceleration of one foot/second. However except for science lessons I never saw the slug being used. I pumped up my tires to 32 lbs/in² not 1 slug/in² but when we went metric instead of giving tire pressure in kg/m² we went to Newtons/m² the Newton be Metric equivalent to the Slug.

It seems the pound or gram are dependent on gravity where the slug or Newton is not, but I and I am sure most other people are not going to become space travellers so what does it matter?

If some one asks what is a Watt I would answer volts x amps x power factor correction, but of course the correct answer should be a Joule per second. But I am an electrician not a scientist. Ask me how bright it is today I would say 16 EV I would not have a clue how many lumen per meter that is. As a photographer I measure light in stops or EV.

And that is what we need for the light bulb. I really don't want to know how many lumen it is what I want to know in a 20 x 10 foot room 8 foot high what settings will I need for my camera. If at ISO 100 and f5.6 I can take a picture at 1/30 second that's good enough. If not I need more light and I have yet to find a lumen and distance to EV (Exposure Value) converter which is not surprising as the lumen is a rubbish unit with many conflicting ways to measure it.
 
Energy has no time. A Joule is one Neutron at a height of one meter. Power however does have time.
So a Joule per second is a Watt. I do think it is easy to get Energy and Power mixed up. This is not helped when units like kWh are used for Energy you see the h for hour and think there is some time component.
As Grizzly has said, in terms of dimensions, I'm afraid that's all wrong. The dimensions of energy include time^-2, hence the dimensions of power include time^-3.

When it comes to units, you can, of course, choose ones which 'hide' some or all of the dimensions, but that doesn't alter the fact that they are there. For example, if you express a speed as mph or km/h, the time dimension is there 'for all to see'. However, if you express it as knots, then you can no longer 'see' the time dimension in the unit, although it is obviously still there. Even 'Watt' does not 'display' any time dimensions, although even you acknowledge that they are there.

Conversely, of course, one could use a unit which makes it appear that a time dimension is present, even when it isn’t. Taking the above example, a “knot.hour” would actually be a measure of distance, and includes no dimensions of time - but the unit makes it look as if it does.

Kind Regards, John
 
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Energy has no time. A Joule is one Neutron at a height of one meter. Power however does have time.
So a Joule per second is a Watt. I do think it is easy to get Energy and Power mixed up. This is not helped when units like kWh are used for Energy you see the h for hour and think there is some time component.
As Grizzly has said, in terms of dimensions, I'm afraid that's all wrong. The dimensions of energy include time^-2, hence the dimensions of power include time^-3.

When it comes to units, you can, of course, choose ones which 'hide' some or all of the dimensions, but that doesn't alter the fact that they are there. For example, if you express a speed as mph or km/h, the time dimension is there 'for all to see'. However, if you express it as knots, then you can no longer 'see' the time dimension in the unit, although it is obviously still there. Even 'Watt' does not 'display' any time dimensions, although even you acknowledge that they are there.

Conversely, of course, one could use a unit which makes it appear that a time dimension is present, even when it isn’t. Taking the above example, a “knot.hour” would actually be a measure of distance, and includes no dimensions of time - but the unit makes it look as if it does.

Kind Regards, John

Sorry energy has no time if we take the electric mountain as an example when they pump the water into the top lake this uses power which includes some time but once the water is in the top lake the water has energy it does not have any time factor if it stays there for one hour or 6 months it does not matter it is just energy. However when it is used that energy is converted into power which again has a time component.

So a lump of coal is energy as is a tank of petrol but once we convert it into power to run a power station or propel a car it becomes power and so has time as a component.
 
Energy has no time.
What do you actually mean by that?


A Joule is one Neutron at a height of one meter.
So energy has length?


So a Joule per second is a Watt.
And a Watt second is a Joule.


I do think it is easy to get Energy and Power mixed up. This is not helped when units like kWh are used for Energy you see the h for hour and think there is some time component.
There is, that's what the h is.

There has to be a time component if you want to use Watts as a component in the way you express how much energy has been used/converted/transferred.

So if you're stating how much energy an oven will use to carry out a given task, and you don't want to say "3.06MJ" but would rather involve Watts then you have to say "0.85 kWh". The time component has to be there.

Just like if you want to use velocity as a component of distance there has to be a time element. You could say that the Earth is 150 Mkm from the Sun, or you could say it's 8.3 light minutes.


With Imperial we had the Poundal which would give a pound an acceleration of one foot/second and the pound would give a slug an acceleration of one foot/second.
Be careful - in the first use of the word "pound" you are talking about mass, and in the second you are talking about force.

screenshot_124.jpg


(Ooh - time components again..... ;) )


I pumped up my tires to 32 lbs/in² not 1 slug/in²
You could not possibly do the latter, as a slug is a unit of mass. The problem here is that "32 lb/in²" is a sloppy term - it should be "32 lbf/in²" - 32 pound-force per square inch.


but when we went metric instead of giving tire pressure in kg/m² we went to Newtons/m²
Yes, because kg is a unit of mass, and what we want is a unit of force. Pressure is force per unit of area.

32psi is about 221kN/m². Or 221 kilo Pascals. Or 2.2 bar.


It seems the pound or gram are dependent on gravity
Not as units of mass. A bag of flour which we say weighs 1 kg here will weigh more or less that that in other places in the universe, but wherever you take it it will always have a mass of 1 kg.


where the slug or Newton is not, but I and I am sure most other people are not going to become space travellers so what does it matter?
It just does.
 
Sorry energy has no time if we take the electric mountain as an example when they pump the water into the top lake this uses power which includes some time but once the water is in the top lake the water has energy
It takes a certain amount energy to pump a given amount of water up a mountain of a given height, and that energy (whether from electricity or whatever) then gets converted into potential energy of the water. How much power it takes to pump the water up the mountain will vary, depending entirely on how quickly one pumps it (i.e. how much time it takes to supply the required amount of energy to pump the water up the mountain).

Kind Regards, John
 
Sorry energy has no time if we take the electric mountain as an example when they pump the water into the top lake this uses power which includes some time but once the water is in the top lake the water has energy
It takes a certain amount energy to pump a given amount of water up a mountain of a given height, and that energy (whether from electricity or whatever) then gets converted into potential energy of the water. How much power it takes to pump the water up the mountain will vary, depending entirely on how quickly one pumps it (i.e. how much time it takes to supply the required amount of energy to pump the water up the mountain).

Kind Regards, John
Yes you have got it energy does not have time component. Power depend on how quickly you pump it so has a time component. Spot on.
 
I do think it is easy to get Energy and Power mixed up. This is not helped when units like kWh are used for Energy you see the h for hour and think there is some time component.
There is, that's what the h is.
Losing the k keeping to just watts to make is simple so replace the watts with a Joule we have a (J/s)/360s removing brackets that's J/s x 360s the s cancels out so W/h = 360 Joules with no time involved it has been cancelled out.

Come on it is rather simple maths for an Electrician.
 
Yes you have got it energy does not have time component. Power depend on how quickly you pump it so has a time component. Spot on.
With respect, you don't seem to understand what we are all saying. Dimensionally (i.e. in terms of physics), both power and energy very much have 'time components - time^-3 and time^-2 (or 1/time² and 1/time³ if you prefer) - even if you choose to use units which fail to 'highlight' that.

If you were a purist physicist and chose (perfectly legitimately) to use only SI base units, you would measure power in units of kg.m²/s³ and you would measure energy in units of kg.m²/s². The 'time component' of both would then be obviously apparent. You're just choosing to think in terms of units which make that less immediately obvious.

Power=Energy/time .... and .... Energy=power*time
Even looked at like that, both have 'time components'.

Kind Regards, John
 
Definition: Energy is the capacity of a physical system to perform work. Energy exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, electrical, or other forms.

According to the law of conservation of energy, the total energy of a system remains constant, though energy may transform into another form. Two billiard balls colliding, for example, may come to rest, with the resulting energy becoming sound and perhaps a bit of heat at the point of collision.

The SI unit of energy is the joule (J) or newton-meter (N * m). The joule is also the SI unit of work.

Where in the above is there any reference to time. Be it a lump of coal or a tank full of petrol or even a bottle of Lucozade they all have energy non have any time involved in any way.
 
The SI unit of energy is the joule (J) or newton-meter (N * m). The joule is also the SI unit of work.
... and, as I said, in SI base units, it is kg.m²/s²
Where in the above is there any reference to time. Be it a lump of coal or a tank full of petrol or even a bottle of Lucozade they all have energy non have any time involved in any way.
There might not be any references to time in any of the definitions you have chosen to to quote, but if you accept that kg.m²/s² is a perfectly correct unit for energy (whether electrical, potential, chemical or whatever), the presence of a 'time element' is quite clear and obvious. If you do not accept that energy can be measured in units of kg.m²/s², then we have a problem!

Kind Regards, John
 

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