Students learn about Pascal's law, an important concept behind the engineering of dam and lock systems, such as the one that Thirsty County wants Splash Engineering to design for the Birdseye River an ongoing hypothetical engineering scenario. Students observe the behavior of water in plastic wate Raise your hand if you've heard of the Panama Canal. What about the Mississippi River? Did you know that both of these major water transportation routes—and many others! It's called a dam and lock system.
Boats and ships get through a waterway by going into a lock, which is a big chamber in the water with moveable gates at each end, then waiting as a valve is opened and the water from that lock flows into the next lock or next body of water if just one lock , raising or lowering the boat automatically. The boats continue into the next lock, and so on, until they reach the end of the dam and lock system. A series of locks enable river vessels to "step" up or down a river or canal from one water level to another.
The multipurpose Lower Monumental Dam and Lock on the Snake River in Washington includes a concrete gravity-type dam with short earthfill abutment embankments, an eight-bay spillway, a single-lift type lock far right structure and two fish ladders. Let's look at this graphic. Then the drain valve and upstream and downstream gates are closed so the chamber water level rises to the upstream level.
Then the upstream gate opens and the boat moves in. To lower the boat, the gates are closed behind it, the filling valve is closed, and the drain valve is opened. The higher water in the lock chamber drains to the downstream level in a few minutes. Then, the downstream gate is opened and the boat moves out on the lower water level. The process is reversed for a boat going upstream. You can think of locks as a step-by-step way to move water vessels through bodies of water that are at different water heights.
Figure 2. Diagram of a lock and dam system shows the steps of "locking through" to move a ship downstream to a lower-water level. Why would engineers go to all this trouble? Why wouldn't they just let boats travel waterways on their own? In what situations would boats need locks?
Let's brainstorm ideas and write them on the board. Write student suggestions on the board. One of the main reasons engineers design and build dam and lock systems is to help big and heavy boats get through shallow or steep river areas. Using dams and locks, massive ships can navigate through shallow or steep sections of river, traveling up and down rivers much further than natural terrain would allow, which helps to increase trade and commerce on waterways.
We also know that putting a dam in a river causes a change in the water level on each side of the dam the reservoir is higher than the river below the dam , so how do boats get through once a dam is in place? Locks create ways for boats to get past large dams as well as other naturally-occurring obstacles such as waterfalls, rapids or sandbars. In the case of the Panama Canal, people dug canals across a continent to create a shorter water transportation route between oceans, and they incorporated locks to adjust for the terrain variations.
Locks help to improve river and waterway navigation. A system of locks and dams on the Upper Mississippi River makes it possible for large barges to travel as far north as St. Paul, Minnesota. Show the Mississippi River on a map of the central US states. Along the Upper Mississippi River between St.
Louis, Missouri, and St. Paul, Minnesota are 29 locks and dams that divide the river into 29 flat pools designed to hold water back to maintain a nine-foot deep shipping channel. That's a lot of locks! Imagine how difficult it would be trying to transport something by boat without the locks. Some boats need the water to be nine-feet deep, and if it got shallower in the summer, they would not be able to pass.
Imagine that you were waiting for delivery of something by boat along this river. If that boat ran into shallow waters it might just be stuck, unable to travel any further, without a lock and dam system. An important consideration when engineers design and create dam and lock systems is that the structures must be designed to withstand the forces of water pushing on them.
Pascal's law describes how water at a given depth exerts the same equal pressure in all directions. Something else we know about water pressure — the deeper the water, the greater the water pressure. For example, at a depth of five meters from the surface, the water pressure is half as great as it is at a depth of 10 meters from the surface. Refer to the associated activity Under Pressure to illustruate Pascal's law and water pressure with a fun and hands-on experiment!
Side view of a lock. Notice the moveable gates and different water levels. Locks enable water vessels to move from one section or body of water at one level to another section of water at another level through river and canal waterways. How does it work? A lock might be described as a huge enclosure set in a water channel with watertight and moveable doors gates on the front and back.
At the point where bodies of water at different levels meet, a dam and lock system bridges the gap by creating a contained area that can individually raise or lower its own water level to step a boat up or down the waterway. See Figure 1 animation , Figure 2 three-part diagram or the attached Dam and Lock Visual Aid for a description of the basic steps to move a ship through a lock.
The principle behind locks is straightforward: The river is an inclined plane whose water moves in and out of locks by gravity. Think of locks as a flight of "water stairs" going up and down a hill. Water is drained from the first lock using gravity until the water level is even with the second one. The downstream gate is opened so the vessel can move into the lower lock, and the process may be repeated numerous times. The lifting and lowering of vessels, some weighing up to 60 tons, is done without a great use of energy.
The deeper you go beneath the water's surface, the more water pressure you'll find. Have you ever dived deep into a pool and thought about the pressure you feel in your ears?
The deeper you go, the more pressure you feel. A lot of people do not realize how strong water can be! Imagine how much water pressure is at the bottom of the ocean. Water pressure is something that scuba divers think about — and engineers. Imagine how strong a structure must be to hold back the force of all the water in a reservoir a dam , or to keep water from going where you do not want it a lock! Who can explain to me how a dam and lock system works?
Let a few students explain. How do locks help improve river navigation? How are gravity and water pressure involved in how locks work? See additional discussion questions and answers in the post-lesson Assessment section. For example, the Earth's mass pulls you down so you stay on the ground instead of flying away. Pascal's law : A hydrostatics principle that says that for all points at the same absolute height in a body of a fluid, the pressure is the same, even if additional pressure is applied on the fluid at some place.
Expressed as force per unit area. Think-Pair-Share: Ask students to think about the following questions and then share their responses with a neighbor. Review as a class.
Points to make: What you are feeling at the bottom of the swimming pool is the water's pressure. The deeper we dive, the more pressure we feel from the weight of more water being above us. Sometimes our ears hurt because of the pressure on our eardrums.
Toss-a-Ball: Ask the following questions to the class and have each student catch and toss a ball while answering. Class Discussion: Ask students the following questions. Listen to their answers. Discuss as a class:. Engineering Drawings: Once students understand how lock and dam systems work, ask them to create preliminary drawings as if they were engineers from Splash Engineering designing a system for their municipality client Thirsty County.
Require that the drawings illustrate where along a river Birdseye River the dam and lock structure will be built, the dimensions of the structure how long, wide and deep , and the number of locks in the structure. For an added challenge of constraining the students' designs, tell them that the river is 50m wide and 8m deep, and the largest vessel permitted to pass through is 10m long. Children can help with locks, but please make sure they are physically able and always supervised. Part of the fun of the canals is the locks, so please stay safe, but involve all your group.
If you are not sure what to do, there are usually other boaters or canal users around who are friendly and will lend a hand. If necessary, moor up and watch other people working the lock until you feel confident to give it a go. Canal locks are the way in which canals can go up and over hills by altering the level of water of the canal. Simply put, you go into the lock when it is nearly empty, fill it up and then cruise out the other end. This lifts the boat up to a higher canal level, or if going the other way lowers the boat down to a lower level if you are letting water out of the lock.
A lock consists of a lock chamber which is brick, stone or metal and holds the water. To allow boats to get in and out, and to keep the water in, there are gates at each end of the lock. Sometimes there is one single lock gate, other times there are two double gates, and these are pushed open by balance beams on the gates. It is only possible to open a gate when the water levels on both sides are the same.
So, the top lock will only open when the lock is full of water, and the bottom gate only opens when the lock is empty or nearly empty. There are paddles on locks which are raised and lowered to control the water flow and alter the level.
The cill is a large raised ledge at the top end of the lock which the top gate shuts against. So, how does a lock work on a canal? There are no pumps or electric motors except on some of the larger commercial traffic or guillotine locks. Narrow locks are wide enough for one boat, but wide locks generally hold two boats side by side.
They are predominantly found in the South or on wide or barge canals. Windlass - You will require a windlass for winding the canal lock paddle mechanism up and down - this is an L shaped handle which is fitted to the spindle on the paddle. Always wind paddles slowly, checking to see what effect the water is having on your boat. Anti-vandal key - You may also require a Waterways Authority key or anti-vandal key to unlock the canal lock paddle mechanism — ask your marina about this when you collect the boat.
Sluices — These are channels in the lock which enable water to pass from one area to another. Paddle gear — This can either be hydraulic or rack and pinion. On the rack and pinion type there is a safety catch or pawl which stops the gears from slipping down and keeps the paddle raised when the windlass is removed. When you have finished winding paddles check the pawl is in position and then take off the windlass. Lock landing — This is a section of the towpath either above or below the lock for boats to moor and either wait to enter the lock or let crew off the boat.
They can also be pontoons reached by a ladder. If this needs adjusting, put the safety catch pawl in place and then start again. Should the safety catch pawl disconnect and the paddle drop your windlass handle could spin round and you may either lose it in the canal or it could hit someone.
To release the safety catch pawl , wind the paddle up a little, take the strain with the windlass, then remove the safety catch pawl and wind down the paddle. When you arrive at a lock, moor up and send at least one of your crew to check whether it's full of water or empty, or if another boat is already using the lock. If the lock is in use, moor up far enough away to avoid the currents while it is being emptied. If the lock is empty of water, open the gates by pushing against the balance beams.
Take the boat in steadily then close the gates. Try to keep the boat in the middle of the lock to avoid anything catching as the water rises. If the lock is full of water, moor up below the lock whilst your crew empty the lock by slowly raising the paddles. When the lock is empty, go in. When the gates are closed, your crew can then move to the far end of the lock and slowly open the top, 'ground' paddles.
These are situated either side of the lock, winding up the ground paddles, followed by any centre lock paddles, if fitted, to fill the lock. Always wind slowly to avoid making a tidal wave in the lock which will throw the boat backwards against the bottom gates.
Leave the pawl or safety catch in place whilst raising the paddles. Once the paddles are up and you are happy with the flow and its effect on the boat, remove the windlass from the mechanism. If you find you need to control the movement of the boat, do it with gentle bursts of throttle - forward if the boat is moving backwards, reverse if the boat is moving forwards.
Your crew must understand the importance of opening the paddles slowly, to prevent the boat moving about too much in the lock.
0コメント