# I have a few questions about the joule/newton

by mpatryluk
Tags: joule or newton
 P: 36 Im not quite sure what it is about this simple concept that i cant get, but im having a very tough time understanding how the concept of a joule makes sense. How can it be the energy expended in applying a newton through a distance of 1 meter? Isnt a newton just a measure of force? So it could represent accelerating a 1kg object by 1 metre per second, but couldnt it also represent accelerating a 5kg object by .2 metres per second? If that's the case, then what does it mean to apply a newton through a distance of 1 meter? Is that only relevant in cases where the weight is 1kg? Because applying a newton to a 5kg object over 1m would be alot more work than that required to do s with a 1kg object
P: 740
 Quote by mpatryluk Because applying a newton to a 5kg object over 1m would be alot more work than that required to do s with a 1kg object
No it wouldn't. The force is the same, and so is the distance, so work must the same also.

To get a feel for it, think in terms of kinetic energy gained(ΔEk=W).
In the first case, you end up with a heavier object moving slower than the lighter object in the latter case.
The kinetic energy of the 5kg body accelerated by 1 Newton (with 0.2m/s^2 acceleration according to F=ma) over 1m will be the same as the kinetic energy of the 1kg body accelerated by 1N(a=1m/s^) over the same distance.
P: 852
 Quote by mpatryluk ...what does it mean to apply a newton through a distance of 1 meter?
It literally means you keep pushing with the force 1 N for however long as it takes to travel a meter. It isn't the same as accelerating the object by a certain amount per time over a meter.

 Because applying a newton to a 5kg object over 1m would be alot more work than that required to do s with a 1kg object
As Bandersnatch shows, applying 1 N to a 5 kg object over 1 m would accelerate it a lot less than 1 N applied to a 1 kg object over the same 1 m.

Imagine expending the same effort throwing a light ball and heavy one. Or imagine taking an engine from a car and putting it in a big truck.

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