SI Unit for Mass

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Molly Posta 1H
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Joined: Wed Sep 30, 2020 10:05 pm

SI Unit for Mass

Postby Molly Posta 1H » Wed Oct 28, 2020 5:16 pm

Out of all the equations we've used so far in units 1 and 2, should mass always be in kg? I've been using g for mass for most of my work, but I noticed while reviewing the De Broglie equation that mass needs to be converted into kg for this example. Do some equations require mass in kg while some use g?

Wil Chai 3H
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Re: SI Unit for Mass

Postby Wil Chai 3H » Wed Oct 28, 2020 5:19 pm

The equations that involve joules as a unit require you to use kg, because 1 J = 1 kg m^2 s^-2 . It's important to note also that all equations with Planck's constant require kg, since h = 6.626x10^-34 J*s.
Last edited by Wil Chai 3H on Wed Oct 28, 2020 5:21 pm, edited 1 time in total.

kateraelDis2F
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Re: SI Unit for Mass

Postby kateraelDis2F » Wed Oct 28, 2020 5:20 pm

Whenever you use DeBroglie, you always want mass in kg. Whether that be the mass of an electron or something else.

Stuti Pradhan 1B
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Re: SI Unit for Mass

Postby Stuti Pradhan 1B » Wed Oct 28, 2020 5:20 pm

Most of the energy equations require kg because Joules = kg⋅m^2⋅s^−2, so you need to use kg to make sure the units cancel. In converting from mass to moles, you just use the molar mass in grams, but otherwise, kg it typically used as it is the SI unit for mass.

Hope this helps!

Nathan Lao 2B
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Re: SI Unit for Mass

Postby Nathan Lao 2B » Wed Oct 28, 2020 5:22 pm

It's probably easier to use kg instead of grams since Planck's constant is given as 6.626x10^/34 kg m^2 s^-1. Cancelling units is pretty easy from there.

Bai Rong Lin 3I
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Re: SI Unit for Mass

Postby Bai Rong Lin 3I » Sun Nov 01, 2020 10:47 pm

Molly Posta 1H wrote:Out of all the equations we've used so far in units 1 and 2, should mass always be in kg? I've been using g for mass for most of my work, but I noticed while reviewing the De Broglie equation that mass needs to be converted into kg for this example. Do some equations require mass in kg while some use g?

It is based on what type of constant you are using and its units I believe, but the majority of the time kg is being used in these constants!

ShinwooKim_3E
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Joined: Wed Sep 30, 2020 10:00 pm

Re: SI Unit for Mass

Postby ShinwooKim_3E » Wed Nov 04, 2020 12:45 am

Molly Posta 1H wrote:Out of all the equations we've used so far in units 1 and 2, should mass always be in kg? I've been using g for mass for most of my work, but I noticed while reviewing the De Broglie equation that mass needs to be converted into kg for this example. Do some equations require mass in kg while some use g?

We should always leave mass in kg when using the De Broglie equation (it's different when talking about stoichiometry or mass measurements of compounds, then we use g)

Kathy_Li_3J
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Re: SI Unit for Mass

Postby Kathy_Li_3J » Sat Nov 07, 2020 5:58 pm

Hi! The SI unit for Mass is kilograms, so I would just assume that the equation uses kilograms unless otherwise stated (e.g. the final units has g instead of kg).

Gicelle Rubin 1E
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Re: SI Unit for Mass

Postby Gicelle Rubin 1E » Sat Nov 07, 2020 6:04 pm

Hi! I am pretty sure mass has to be in kg. In examples where I'm given grams, I convert to kg before using any equation.


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