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### Units of Energy

Posted: Tue Oct 16, 2018 3:41 pm
How is 1 Joule expressed in terms of SI base units? When would we convert J into SI base units in order to solve an equation?

### Re: Units of Energy

Posted: Tue Oct 16, 2018 3:51 pm
1 Joule = 1 kg * m^2 * s^-2, which can also be written as kg*m^2/s^2

You can convert Joules to SI units when you're using dimensional analysis to help you solve a problem. This could come in handy whenever you're solving for energy, as energy is often measured in Joules.

### Re: Units of Energy

Posted: Tue Oct 16, 2018 8:30 pm
Also, putting Joules in terms of SI units can be especially handy when seeing if units make sense and cancel correctly. For example, in calculating wavelength for light, the kg, seconds, and one m cancel leaving your answer in m (meters).

### Re: Units of Energy

Posted: Wed Oct 17, 2018 1:01 pm
It is best to break down the units of a joule when you are also trying to calculate energy. Often times problems will try to trick you by giving velocity in miles/hour or they will give you mass in grams. When you approach a problem like this, it is important to know that you need values in kg and m/s in order to solve for energy in joules.

### Re: Units of Energy

Posted: Wed Oct 17, 2018 5:07 pm
I personally always like to write out the SI units for Joules in order to make sure the units match with everything else and I am not using the wrong variable. However in terms of when you actually NEED to write out the SI units, I would say whenever the question asks you to, otherwise there is no need.

### Re: Units of Energy

Posted: Thu Oct 18, 2018 7:53 pm
The way that I remember the SI units for a Joule is by writing out the equations from physics

E = F*d
also F=ma
so,
J=(kg*m*(s^-2))*m
J=kg*m^2*s^-2