# Where does the energy come from in a canal lock?

• amalgamma
In summary: I'm not even going to apologize for wasting your time. I'm going to try and do something else.In summary, a lock works by either letting water flow in from a higher level and lose potential energy, or by using energy to pump water into the lock. When the lock is full, the water is back at its original level and in a hydro dam, the water's energy is harnessed through a turbine. In a lock, the water simply flows there whether or not there is a load present. The energy to fill the lock is ultimately derived from the sun through the water cycle.
amalgamma
You can lift a zillion-ton ore barge 30 feet like magic, and nothing seems to have done the work. Help me get it.

There's a difference in water level.

Either the water that filled the lock flowed from a higher level and lost some potential energy, or else the water was pumped into the lock and energy was used to drive the pump.

willem2 said:
There's a difference in water level.

And ...? The water would rise just the same if the barge weren't there.

AlephZero said:
Either the water that filled the lock flowed from a higher level and lost some potential energy, or else the water was pumped into the lock and energy was used to drive the pump.

When the lock is full again, the water is back where it was, and in, say, a hydro dam, the water is slowed going through the turbine. In a lock , it simply flows there whether there is a load or not. And what kind of canal lock pumps water, when all you have to do is let the higher water in? What am I not seeing?

amalgamma said:
And ...? The water would rise just the same if the barge weren't there.

If there's no barge in the lock, more water has to flow in, in order to reach the same level. In fact, the mass of the "extra" water equals the mass of the barge, because the barge displaces a mass of water equal to its own mass.

amalgamma said:
When the lock is full again, the water is back where it was, and in, say, a hydro dam, the water is slowed going through the turbine. In a lock , it simply flows there whether there is a load or not. And what kind of canal lock pumps water, when all you have to do is let the higher water in? What am I not seeing?
Water that would have flowed through the turbine flows through the lock instead.

jtbell said:
If there's no barge in the lock, more water has to flow in, in order to reach the same level. In fact, the mass of the "extra" water equals the mass of the barge, because the barge displaces a mass of water equal to its own mass.

I'm sure I'm being thick, but are you saying that the energy comes from the water that doesn't enter the lock? If you fill the lock with the same amount of water it would hold if the barge were there, its surface would be at a lower level, and more potential energy would have been lost than if it had lifted a barge. I'm hoping you can spot the idiotic misapprehension in what I'm thinking here.

russ_watters said:
Water that would have flowed through the turbine flows through the lock instead.

What? At what point does the flow give up energy in a lock?

amalgamma said:
What? At what point does the flow give up energy in a lock?
When you open the entrance gate and let the water in the lock spill into the lower level.

russ_watters said:
When you open the entrance gate and let the water in the lock spill into the lower level.

Right, which it would do anyway.

amalgamma said:
Right, which it would do anyway.
...but through a turbine. You lose energy by just dumping the water instead of running it through a turbine.

amalgamma said:
You can lift a zillion-ton ore barge 30 feet like magic, and nothing seems to have done the work. Help me get it.
Ultimately the answer is the sun. Let's deal with a purely mechanical lock and a ship going upstream: A boat enters the lock and the gate closes. The gate before them releases water from upstream which raises the boat. The gate them opens and the boat proceeds.

This water must be bought back up at some point and this is achieved by the hydrosphere cycle i.e. the downstream water eventually evaporates and rains again on land.

Is this the answer you are looking for?

jtbell said:
If there's no barge in the lock, more water has to flow in, in order to reach the same level. In fact, the mass of the "extra" water equals the mass of the barge, because the barge displaces a mass of water equal to its own mass.

amalgamma said:
I'm sure I'm being thick, but are you saying that the energy comes from the water that doesn't enter the lock?

The point I'm trying to make is that it takes the same amount of energy to fill the lock so that the water line ends up at a certain level, regardless of whether there is a boat in the lock or not. With the boat in the lock, you have to lift x kilograms of boat and y kilograms of water. Without the boat in the lock, you have to lift x+y kilograms of water.

If you fill the lock with the same amount of water it would hold if the barge were there, its surface would be at a lower level

The purpose of a lock is to get the water level up (or down) to a certain point, namely the level that matches the water level outside the lock at the exit end. So if the barge isn't there, you have to add more water if you're going upwards, or drain more water if you're going downwards.

Ryan_m_b said:
Ultimately the answer is the sun. Let's deal with a purely mechanical lock and a ship going upstream: A boat enters the lock and the gate closes. The gate before them releases water from upstream which raises the boat. The gate them opens and the boat proceeds.

This water must be bought back up at some point and this is achieved by the hydrosphere cycle i.e. the downstream water eventually evaporates and rains again on land.

Is this the answer you are looking for?

I think I grok the water cycle. I'd like to apologize for getting turned around back there---I got the entrance gate and the exit gate reversed in my head somehow. I also grok a lock.

Your answer does help if I imagine using the same water over again. I'm still a bit baffled by the seeming effortlessness of the process. Therer are many unintuitive phenomena in nature, and I guess I'll have to accept this as one more. I never could get my head around potential energy, anyway---it always seemed like giving a name to the inscrutable, treating energy as a substance like an alchemist or something.

Good point, jtbell, and let me expand to help clarify.

There are actually two different sources of loss being discussed:

1. In a real lock, water is just allowed to flow through when the gates are opened (or valves and pipes, more likely). This loss could theoretically be eliminated by putting turbines in. You'd have one turbine by the high side gate to recover energy from filling the lock and another turbine by the low side gate to recover energy from emptying the lock. This volume of water is the length and width of the lock times the lift height. At first glance, this appears to be all of the energy required, which would imply that the lift is free, but it isn't...

2. When a ship enters the lock at the bottom it pushes out a parcel of water equal to its own displacement. When it leaves at the top, it allows back in the same volume of water. That volume of water sneaks past the turbines by going through the open gates instead of through the pipes and turbines. That's the energy that is really expended and "lost" to lift the ship.

Couldn't we stick a dam on the Panama canal and generate a lot of energy that way?

Some energy could be gained from tides, if the canal would be flat (or had a connection at sea level). But the panama canal is long, the height difference is not very large and the canal is not at sea level at the moment. You could try to get some energy from the locks, as water from rivers flows down there. But I doubt that this would give you much power.

It might help if you imagine that at first that boat is anchored fast to the riverbed. When the water flows in from upstream it floods over the (watertight) boat. Now release the boat and see the weight of descending water supplying the energy to lift the rising boat.

amalgamma said:
I'm still a bit baffled by the seeming effortlessness of the process. Therer are many unintuitive phenomena in nature, and I guess I'll have to accept this as one more. I never could get my head around potential energy, anyway---it always seemed like giving a name to the inscrutable, treating energy as a substance like an alchemist or something.

There is loads of (solar) energy involved in evaporating a volume of water that is equivalent to the weight of the boat. OK, it's "free" energy but the Nuclear reactions in the Sun produce 1kW on every square metre of the Earth's surface (at the Equator). If you imagine that weight of water falling (as rain) into a large bucket on one side of a huge see-saw, then the boat would also be lifted up. That would be "effortless" too and you could raise the boat up to the height of the raincloud, too.

You are quite justified in feeling uneasy about Potential Energy as a commodity. Energy is not an easy concept, even though it's something very familiar that our lives revolve around. It was a smart move when Scientists made the connection between all the various forms of energy. Joule did very well to put the mockers on the old 'Caloric' theory of heat.

## 1. Where does the energy come from in a canal lock?

The energy in a canal lock comes from gravity. The lock gates are opened or closed to allow the water to flow in or out, and the force of gravity is what moves the water and raises or lowers the boats.

## 2. How is the energy harnessed in a canal lock?

The energy in a canal lock is harnessed by using a system of gates and valves. When the upper gates are closed and the lower gates are opened, the water from the upper level flows down into the lower level, pushing the boat along with it. When the lower gates are closed and the upper gates are opened, the water from the lower level flows up into the upper level, again moving the boat with it.

## 3. Is any other source of energy used in a canal lock?

In some cases, additional sources of energy may be used in a canal lock, such as hydraulic power or electric motors. These can help to supplement the force of gravity, but the basic principle of using water to move boats remains the same.

## 4. How does the energy in a canal lock affect the environment?

The energy in a canal lock has a minimal impact on the environment, as it is a relatively low-energy and low-impact method of transportation. However, it is important for lock operators to properly maintain and repair the locks to prevent any potential negative effects on the surrounding ecosystem.

## 5. Can the energy in a canal lock be used for other purposes?

In some cases, the energy in a canal lock may be used for other purposes, such as generating electricity. This is often done through the use of hydroelectric turbines, which harness the energy of the moving water to generate power. However, this is not a common practice and is typically only done in larger canal systems.

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