The watt-second is a unit of energy that represents the amount of work done when a power of one watt is sustained for one second. This unit is a direct way to visualize energy transfer in everyday activities. Interestingly, while it may sound abstract, this unit can be directly applied to understand how quick appliances like LED lights or small electronic devices consume energy. For example, a modern LED bulb that consumes 10 watts of power will use 10 watt-seconds of energy every second it is on.
While commonly overshadowed by the more familiar joule, the watt-second is essentially equivalent to one joule. Its simplicity in denoting power over time makes it a cornerstone concept in physics and engineering, where it is applied to calculate specific energy transfers and efficiency in varied systems. Exploring this unit helps bridge the gap between theoretical energy calculations and practical everyday energy use.
The kilojoule, abbreviated as kJ, is a unit of energy in the International System of Units. While it may not be as commonly recognized as calories in everyday conversation, the kilojoule is actually the standard metric unit for quantifying energy. Fascinatingly, 1 kilojoule is equivalent to 0.239 calories, making it a handy unit for converting nutritional information, especially in countries that primarily use the metric system.
Interestingly, the term “joule” is named after the English physicist James Prescott Joule, who studied the nature of heat and discovered its relationship to mechanical work. This unit has applications far beyond nutrition, including physics, chemistry, and engineering, where it measures various types of energy transformations, from kinetic to thermal. Understanding kilojoules can deepen our appreciation of energy, highlighting the intricate balances that power our world and our bodies.
| Watt-seconds | Kilojoules |
|---|---|
0
Ws
|
0
kJ
|
100
Ws
|
0.1
kJ
|
200
Ws
|
0.2
kJ
|
300
Ws
|
0.3
kJ
|
400
Ws
|
0.4
kJ
|
500
Ws
|
0.5
kJ
|
600
Ws
|
0.6
kJ
|
700
Ws
|
0.7
kJ
|
800
Ws
|
0.8
kJ
|
900
Ws
|
0.9
kJ
|
1000
Ws
|
1
kJ
|
1100
Ws
|
1.1
kJ
|
1200
Ws
|
1.2
kJ
|
1300
Ws
|
1.3
kJ
|
1400
Ws
|
1.4
kJ
|
1500
Ws
|
1.5
kJ
|
1600
Ws
|
1.6
kJ
|
1700
Ws
|
1.7
kJ
|
1800
Ws
|
1.8
kJ
|
1900
Ws
|
1.9
kJ
|
2000
Ws
|
2
kJ
|
2100
Ws
|
2.1
kJ
|
2200
Ws
|
2.2
kJ
|
2300
Ws
|
2.3
kJ
|
2400
Ws
|
2.4
kJ
|
2500
Ws
|
2.5
kJ
|
2600
Ws
|
2.6
kJ
|
2700
Ws
|
2.7
kJ
|
2800
Ws
|
2.8
kJ
|
2900
Ws
|
2.9
kJ
|
3000
Ws
|
3
kJ
|
3100
Ws
|
3.1
kJ
|
3200
Ws
|
3.2
kJ
|
3300
Ws
|
3.3
kJ
|
3400
Ws
|
3.4
kJ
|
3500
Ws
|
3.5
kJ
|
3600
Ws
|
3.6
kJ
|
3700
Ws
|
3.7
kJ
|
3800
Ws
|
3.8
kJ
|
3900
Ws
|
3.9
kJ
|
4000
Ws
|
4
kJ
|
4100
Ws
|
4.1
kJ
|
4200
Ws
|
4.2
kJ
|
4300
Ws
|
4.3
kJ
|
4400
Ws
|
4.4
kJ
|
4500
Ws
|
4.5
kJ
|
4600
Ws
|
4.6
kJ
|
4700
Ws
|
4.7
kJ
|
4800
Ws
|
4.8
kJ
|
4900
Ws
|
4.9
kJ
|
5000
Ws
|
5
kJ
|
5100
Ws
|
5.1
kJ
|
5200
Ws
|
5.2
kJ
|
5300
Ws
|
5.3
kJ
|
5400
Ws
|
5.4
kJ
|
5500
Ws
|
5.5
kJ
|
5600
Ws
|
5.6
kJ
|
5700
Ws
|
5.7
kJ
|
5800
Ws
|
5.8
kJ
|
5900
Ws
|
5.9
kJ
|
6000
Ws
|
6
kJ
|
6100
Ws
|
6.1
kJ
|
6200
Ws
|
6.2
kJ
|
6300
Ws
|
6.3
kJ
|
6400
Ws
|
6.4
kJ
|
6500
Ws
|
6.5
kJ
|
6600
Ws
|
6.6
kJ
|
6700
Ws
|
6.7
kJ
|
6800
Ws
|
6.8
kJ
|
6900
Ws
|
6.9
kJ
|
7000
Ws
|
7
kJ
|
7100
Ws
|
7.1
kJ
|
7200
Ws
|
7.2
kJ
|
7300
Ws
|
7.3
kJ
|
7400
Ws
|
7.4
kJ
|
7500
Ws
|
7.5
kJ
|
7600
Ws
|
7.6
kJ
|
7700
Ws
|
7.7
kJ
|
7800
Ws
|
7.8
kJ
|
7900
Ws
|
7.9
kJ
|
8000
Ws
|
8
kJ
|
8100
Ws
|
8.1
kJ
|
8200
Ws
|
8.2
kJ
|
8300
Ws
|
8.3
kJ
|
8400
Ws
|
8.4
kJ
|
8500
Ws
|
8.5
kJ
|
8600
Ws
|
8.6
kJ
|
8700
Ws
|
8.7
kJ
|
8800
Ws
|
8.8
kJ
|
8900
Ws
|
8.9
kJ
|
9000
Ws
|
9
kJ
|
9100
Ws
|
9.1
kJ
|
9200
Ws
|
9.2
kJ
|
9300
Ws
|
9.3
kJ
|
9400
Ws
|
9.4
kJ
|
9500
Ws
|
9.5
kJ
|
9600
Ws
|
9.6
kJ
|
9700
Ws
|
9.7
kJ
|
9800
Ws
|
9.8
kJ
|
9900
Ws
|
9.9
kJ
|
10000
Ws
|
10
kJ
|
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