Conversion between Watt and Joule

  • Thread starter jamiebean
  • Start date
  • Tags
    Joule Watt
In summary: All you'd need is a tiny piece of one of those apples, provided you had a comparable amount of anti-apple. :woot:Specific power isn't totaly obscure, it's used for engines or batteries where weight matters, such as aircraft.I think we need the OP to provide more context to his...question.
  • #1
55
3
example)
E = 2734.2 joules per gram
P = 2.73 x 109 watt/gram

q: How can this conversion work?

E = 21000 joules per gram
P = ?
 
Physics news on Phys.org
  • #2
jamiebean said:
example)
E = 2734.2 joules per gram
P = 2.73 x 109 watt/gram

q: How can this conversion work?

E = 21000 joules per gram
P = ?
what do you want to convert? Joule is unit of energy, Watt is unit of Power. Those are different physical quantities.
 
  • #3
1 watt = 1 joule per second
 
  • Like
Likes berkeman
  • #4
lomidrevo said:
what do you want to convert? Joule is unit of energy, Watt is unit of Power. Those are different physical quantities.

E=energy
P=power

s the conversion above possible??
 
  • #5
As I said, those are different quantities, so I miss any meaningful reason for such conversion. Maybe, what you want to rather know, is the relationship between them. At the most basic level, we can define Power as the rate of doing work (using energy), or amount of work done per time interval and the relationship between the units is ##W = \frac{J}{s}##
 
  • #6
jamiebean said:
s the conversion above possible??
If you know the time.
 
  • #7
A.T. said:
If you know the time.

I don't think that conversion is the correct word here. We could also ask (as analogy to Energy and Power): What is the conversion between Distance and Speed? It doesn't have any physical meaning. But we can say there is close relationship between them, when describing motion of an object.
 
  • Like
Likes Asymptotic and russ_watters
  • #8
jamiebean said:
example)
E = 2734.2 joules per gram
P = 2.73 x 109 watt/gram

q: How can this conversion work?

E = 21000 joules per gram
P = ?

If the two systems are similar I would try using ratios (scaling)

P2/E2 = P1/E1
So..
P2 = (P1/E1) * E1P2 = (2.73 * 10^9 / 2734.2) * 21000

Without more information it's not possible to say if this is the correct approach. Not everything scales linearly like this.
 
  • #9
jamiebean said:
example)
E = 2734.2 joules per gram
P = 2.73 x 109 watt/gram

q: How can this conversion work?

##\frac{2734.2 \ \mathrm{J/g}}{2.73 \times 10^9 \ \mathrm{W/g}}\approx 1.00\times10^{-6} \ \mathrm{s}##

This calculation tells us that if you delivered energy at a rate of 2.73 x 109 J/s for 1.0 x 10-6 seconds you'd deliver a total of about 2734.2 J of energy. There are no conversions involved here.

It's like saying your position changes by 60 miles every hour when you move at a speed of 60 mi/h. If you do this for, say 2 hours, you'll travel a distance of 120 miles. Note that I'm not converting 60 mi/h to 120 mi. Again, there are no conversions here.

Conversions are present when two quantities are measuring the same thing but in different units. When you measure a speed of 60 mi/h you're measuring a speed, not a distance. And when you measure a distance of 120 mi you're measuring a distance, not a speed. Speed is the rate at which distance changes.

The watt is a unit of power, not energy. The joule is a unit of energy, not power. Power is the rate at which energy is transferred.
 
  • Like
Likes russ_watters and OmCheeto
  • #10
jamiebean said:
example)
E = 2734.2 joules per gram
P = 2.73 x 109 watt/gram

q: How can this conversion work?

E = 21000 joules per gram
P = ?
Can't see that anyone has done it so far, but I'd like to point out that the equations are incorrect.
Joules/gram is "specific energy", not just energy.
Likewise, watts/gram is "specific power". Which happens to be such an obscure thing, that wiki doesn't even have an entry for it.
They do list two examples though, in their "power density" page:
Stars/hydrogen: 1.84 watts/gram
Plutonium: 1940 watts/gram​

This might seem trivial, and it appears that everyone has simply worked around it, as "grams" simply cancels out, but it confused me at first.

In my confusion, I decided to find out the specific energy of something, and randomly picked apples.
Serendipitously, they have a surprisingly similar specific energy to your number: 2200 joules/gram
From that, I determined that I'd have to eat 6,700 apples per second, at the given "specific power".
Which is when I think I went back to your original post, as that seemed like a lot of apples to consume, per second.
 
  • Like
Likes russ_watters
  • #11
OmCheeto said:
Serendipitously, they have a surprisingly similar specific energy to your number: 2200 joules/gram
From that, I determined that I'd have to eat 6,700 apples per second, at the given "specific power".
Which is when I think I went back to your original post, as that seemed like a lot of apples to consume, per second.
Yes, but that's just the chemical energy released in digesting apples. You'll need a lot less if you fuse them.
 
  • Like
Likes lomidrevo
  • #12
russ_watters said:
Yes, but that's just the chemical energy released in digesting apples. You'll need a lot less if you fuse them.

All you'd need is a tiny piece of one of those apples, provided you had a comparable amount of anti-apple. :woot:
 
  • Like
Likes lomidrevo and russ_watters
  • #13
Specific power isn't totaly obscure, it's used for engines or batteries where weight matters, such as aircraft.
 
  • #14
I think we need the OP to provide more context to his question.
 
  • #15
CWatters said:
Specific power isn't totaly obscure, it's used for engines or batteries where weight matters, such as aircraft.
Yes. I remember the "power to weight" ratios listed for cars, back when I was a youngster.
Interesting how "specific power" is mostly only a concern of rocket scientists, 16 year olds, and electric car manufacturers.
hmmmm...
Yes.
Where is that OP?
 
  • #16
a watt-second is a joule.
 
  • Like
Likes OmCheeto

1. What is the relationship between Watt and Joule?

Watt and Joule are both units of measurement for energy. Watt measures the rate of energy transfer, while Joule measures the amount of energy transferred. Therefore, Watt and Joule are related by the equation: 1 Joule = 1 Watt x 1 second.

2. How do you convert Watts to Joules?

To convert Watts to Joules, you can use the formula: Joules = Watts x time (in seconds). For example, if you have 100 Watts of power being used for 10 seconds, the conversion would be: 100 Watts x 10 seconds = 1000 Joules.

3. Can you convert Joules to Watts?

No, Joules and Watts are not interchangeable units. Joules measure energy, while Watts measure power. However, you can convert between the two by dividing Joules by the amount of time in seconds, as shown in the previous example.

4. How is the conversion between Watt and Joule useful in everyday life?

The conversion between Watt and Joule is useful in understanding the amount of energy used or transferred in various activities or devices. For example, knowing the Wattage of a lightbulb and the length of time it is used can help you calculate the amount of Joules of energy used.

5. Are there any other units related to Watt and Joule?

Yes, there are other units related to Watt and Joule, such as kilowatt (kW) and kilojoule (kJ). These are larger units, with 1 kW equaling 1000 Watts, and 1 kJ equaling 1000 Joules.

Back
Top