- #1
44HP
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Hi Newbie here so please go easy on me..!
To keep this within my ability to understand can we please live in the perfect world of the junior physics class i.e. uniform density, no friction g=10 etc - thanks
I understand that 'weight' is mass x g
So the weight of something is how hard the Earth is 'sucking'
that's why things weight differently on Earth and the Moon
But the objects mass remains the same...
Now I'm arguing with somebody (he's an engineer and I'm a pen pusher so I'm guessing he'd be right) on another forum about things like energy and momentum so we are slinging p1v1=p2v2 and e=(mv^2)/2 at each other.
The other chap is telling me the weight of something needs to be converted from pounds weight to pounds force before we apply the equations...
I don't get this, I thought for example 1 litre of water weighed 1kg and also has 1kg of mass.
This came about because I challenged his use of the gravitational constant in an equation to calculate the energy and momentum of an object. When I asked why it was there I got the answer above.
I'm perfectly prepared to admit I'm wrong but can some body shed some light?
And as an aside - does the term weight really get used in physics? Or is it a term used to allow regular
folk get a grip on something you guys would call potential energy or something LOL
Thanks in advance...
To keep this within my ability to understand can we please live in the perfect world of the junior physics class i.e. uniform density, no friction g=10 etc - thanks
I understand that 'weight' is mass x g
So the weight of something is how hard the Earth is 'sucking'
But the objects mass remains the same...
Now I'm arguing with somebody (he's an engineer and I'm a pen pusher so I'm guessing he'd be right) on another forum about things like energy and momentum so we are slinging p1v1=p2v2 and e=(mv^2)/2 at each other.
The other chap is telling me the weight of something needs to be converted from pounds weight to pounds force before we apply the equations...
the energy and momentum equations both list Mass as a factor. The gravitational constant is necessary to convert the weight of the object (pounds force) to Mass (pounds-mass). When you weigh an object on a scale that is a reading in pounds-force, but for our energy and momentum equations we need pounds-mass.
I don't get this, I thought for example 1 litre of water weighed 1kg and also has 1kg of mass.
This came about because I challenged his use of the gravitational constant in an equation to calculate the energy and momentum of an object. When I asked why it was there I got the answer above.
I'm perfectly prepared to admit I'm wrong but can some body shed some light?
And as an aside - does the term weight really get used in physics? Or is it a term used to allow regular
Thanks in advance...