[–] kurfu 0 points 3 points (+3|-0) ago 

Step 3 - pushing the float back to the bottom of the silo would require outside energy.


[–] NiklausTheNaked [S] 0 points 1 points (+1|-0) ago  (edited ago)

I understand that loading the float into the silo would require some energy, as would pushing it off the side of the silo, but can't that be overcome by just making the silo taller, therefore generating more energy when dropping it? It will take the same amount of energy to load the float into a 30ft silo as it would a 3000ft silo. Or am I missing something?


[–] kurfu 0 points 2 points (+2|-0) ago 

Actually, it would take more energy to push the float down into a longer silo.

The thing is, when you first push the float to the bottom of the water, you are using outside energy to do so, and storing kinetic energy in the float. However, all that kinetic energy is used up once the float rises back to the top of the water. You then need more outside energy to push the float over the side, where you will use gravitational energy on its way down, and that is all gone once it hits the ground. And now you're right back at the beginning - you need to somehow get the float back under water at the bottom of the silo, but you've exhausted all your potential energy at this point... so, you are back to needing outside energy yet again.

It's basically like rolling a ball down a hill - once you reach the bottom, you have to spend energy to get it back to the top. In your case, its the opposite, once the float gets to the top of the water, you have to spend energy to get it back down to the bottom.


[–] ghotioninabarrel 0 points 1 points (+1|-0) ago 

put the object back in the bottom of the silo; repeat.

Buoyancy happens because the object is displacing water. Putting aside practical (how do you do that?) concerns, getting the object to the bottom of the silo requires pushing a lot of water upwards. Which is more massive than the object, so takes more energy than you'd get from the object falling.


[–] Veridic 0 points 1 points (+1|-0) ago 

Because loading the buoyant object would take more energy than loading a neutral object. This is because the pressure at the base of the silo. An example of a neutral object would be water, which reduces the system to a pump and fountain.


[–] stolencatkarma 1 points -1 points (+0|-1) ago  (edited ago)

Let's modify this a little bit. A pully system attached to a underwater ballon.

The balloon will be filled with air so it rises and creates force. One it reaches the top we release the air so it falls back to the bottom.

Saves energy from moving it off to the side and getting it back underwater.

We riff about stuff like this in /v/talkscience