Little physics question: potential energy / free fall

Tips, advice and tips to lower your consumption, processes or inventions as unconventional engines: the Stirling engine, for example. Patents improving combustion: water injection plasma treatment, ionization of the fuel or oxidizer.
User avatar
Remundo
Moderator
Moderator
posts: 15995
Registration: 15/10/07, 16:05
Location: Clermont Ferrand
x 5189




by Remundo » 07/04/10, 16:39

Hi buddies...

Elephant talks about bringing the mass down ... by raising another of the lower mass.

I have the impression that you forget that the latter takes the potential energy of gravity during its ascent. :P

The kinetic energy acquired by the heaviest mass is therefore much lower than that which would be acquired by free fall ...

Let 1 be the index for mass 1,
Let 2 be the index for mass 2

We assume the altitude h for the descending mass, and 0 for the rising. At the end of the movement, the altitudes are swapped.

The system evolves to constant mechanical energy. The mechanical energy balance gives:


m1 gh = 1/2 (m1 v1² + m2 v2²) + m2 gh

As v1 = v2 by inextensibility of the cable ...

(m1 + m2) v² = 2gh x (m1-m2)

From where v² = 2gh (m1-m2) / (m1 + m2)

When m2 = 0, we find the famous expression "v² = 2gh" of free fall.
0 x
Image
User avatar
zorglub
I posted 500 messages!
I posted 500 messages!
posts: 501
Registration: 24/11/09, 10:12




by zorglub » 07/04/10, 17:01

except that in the case cited in reference, we slow down the descent of the main weight by another mass which obviously says to be taken into account, which should change the result

damn, I had not read the previous message! which must be the obvious mathematical solution
0 x
every morning you look naked in a large ice after 3 minutes you will see that your home and your worst picture ......
User avatar
zorglub
I posted 500 messages!
I posted 500 messages!
posts: 501
Registration: 24/11/09, 10:12




by zorglub » 07/04/10, 17:07

in summary the energy of the mass which "goes down" is the result of the energy of the mass which falls minus the energy of that which goes up
ignoring friction
0 x
every morning you look naked in a large ice after 3 minutes you will see that your home and your worst picture ......
User avatar
elephant
Econologue expert
Econologue expert
posts: 6646
Registration: 28/07/06, 21:25
Location: Charleroi, center of the world ....
x 7




by elephant » 07/04/10, 19:16

Aaah Remundo to the rescue!

Elephant talks about bringing the mass down ... by raising another of the lower mass.


Not quite !

In both cases, it is about harnessing energy, of course. But in the second case, the mass is indeed free to fall with an acceleration g, we want to recover its kinetic energy, plus its weight when it hits the ground heavily (ouch :D )
0 x
elephant Supreme Honorary éconologue PCQ ..... I'm too cautious, not rich enough and too lazy to really save the CO2! http://www.caroloo.be
User avatar
Remundo
Moderator
Moderator
posts: 15995
Registration: 15/10/07, 16:05
Location: Clermont Ferrand
x 5189




by Remundo » 08/04/10, 18:11

Hi Elephant,

I do not understand well because a weight is not an energy ... :?

En the absence of any dissipation and in free fall, you can only recover mgh on impact. 8)
0 x
Image
Christophe
Moderator
Moderator
posts: 79126
Registration: 10/02/03, 14:06
Location: Greenhouse planet
x 10974




by Christophe » 08/04/10, 18:13

Remundo wrote:I do not understand well because a weight is not an energy ... :?


A weight is a force.

It depends on the point of view ... it can be a potential energy ... in both senses of the word!

A mass at X m height = energy potentially released if the mass "falls".
0 x
User avatar
elephant
Econologue expert
Econologue expert
posts: 6646
Registration: 28/07/06, 21:25
Location: Charleroi, center of the world ....
x 7




by elephant » 08/04/10, 20:56

Remundo:

you're right, but going down (quickly or slowly), it can produce a job: going up an elevator or smashing a floor (or squeaking a piiiiiiiiiied! : Cry: )
0 x
elephant Supreme Honorary éconologue PCQ ..... I'm too cautious, not rich enough and too lazy to really save the CO2! http://www.caroloo.be
Aumicron
Éconologue good!
Éconologue good!
posts: 387
Registration: 16/09/09, 16:43
Location: Bordeaux




by Aumicron » 14/04/10, 09:56

For formula pros, a quick question on this subject:

https://www.econologie.com/forums/petite-que ... t9597.html

Goods.
0 x
To argue.

Back to "Special motors, patents, fuel consumption reduction"

Who is online ?

Users browsing this forum : No registered users and 236 guests