Register to reply

I have a few questions about the joule/newton

by mpatryluk
Tags: joule or newton
Share this thread:
mpatryluk
#1
Jul31-14, 09:46 AM
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
Phys.Org News Partner Physics news on Phys.org
UCI team is first to capture motion of single molecule in real time
And so they beat on, flagella against the cantilever
Tandem microwave destroys hazmat, disinfects
Bandersnatch
#2
Jul31-14, 10:00 AM
P: 740
Quote Quote by mpatryluk View Post
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.
olivermsun
#3
Jul31-14, 10:51 AM
P: 852
Quote Quote by mpatryluk View Post
...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.


Register to reply

Related Discussions
Newton to Joule ? General Physics 3
Newton's Third Law Questions Introductory Physics Homework 4
How to integrate Joule's First Law (Joule Heating)? Advanced Physics Homework 2
Two questions about Newton's law Introductory Physics Homework 6
Some Newton's Law Questions. Introductory Physics Homework 9