## General Question about Joules [ENDORSED]

$E=hv$

Arie Hakimi 1L
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### General Question about Joules

So, I understand that a Joule is a measure of energy. 1 Joule is also equal to 1 kg*m^2/s^2,
but what exactly does this mean?

Just from looking at it, I would assume that 1 Joule of energy is the equivalent force to accelerate 1 kg for 1 meter (?), but if anyone knows the true definition of a Joule and can clarify its conversion that would be great.

Andy_Yousif_1A
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### Re: General Question about Joules  [ENDORSED]

A joule is a derived unit of energy in the International System of Units. It is equal to the energy transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one meter.

Yashaswi Dis 1K
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Joined: Fri Sep 29, 2017 7:04 am

### Re: General Question about Joules

Hi,

A Joule is the definition as mentioned above. However, to help with your calculations and unit conversions, A Joules is also equal to kg((m/s)^2). Hope that helps!

David Zhou 1L
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Joined: Fri Sep 29, 2017 7:04 am

### Re: General Question about Joules

Also for the purpose of problem-solving in this unit, it's extremely helpful to keep the kg*(m^2/s^2) definition of the Joule in mind in order to make error checking much easier. If at the end of a problem you see that your units are wrong, you know somewhere along the line something went wrong.

For example, in work function problems, and really any problem relating kinetic energy to 1/2*mv^2, it's useful to see that the units in this are kg for mass and m/s for velocity. I often forget to square the velocity for whatever reason, so I always make sure to check if my kinetic energy units are kg*(m/s)^2 ==> kg*(m^2/s^2).

Also in de Broglie's relation problems, you have to divide Planck's constant, with units J*s, by momentum, with units kg*(m/s). This gives you the wavelength in meters.

Tatiana R Dis 3E
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### Re: General Question about Joules

A joule is defined as: the SI unit of work or energy, equal to the work done by a force of one newton when its point of application moves one meter in the direction of action of the force, equivalent to one 3600th (60^2) of a watt-hour.

Posts: 32
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### Re: General Question about Joules

Hi! The reason that Joules can also refer to kg(v.s) is because that is the work equation and that is the energy expended moving a mass of a given amount at a certain velocity.

Gabi Landes 1-H
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### Re: General Question about Joules

Why do we often use "joule seconds"? In stead of J.s^-1?

Chem_Mod
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### Re: General Question about Joules

Whenever we see Planck's constant, you are using J*s.

J/s in a unit of energy and 1 J/s is a 1 Watt. You may have heard of this unit before.