Fish Bouyancy (Natalie Realegeno)

• Title: How do fish float, sink, or hoover in water?

Principle(s) Investigated: Mass, density, Buoyancy, and buoyant force.

Water has a buoyant force, which means it has a natural force that pushes up towards the surface.

When an object is submersed in water, the pressure exerted on it increases with depth.

The objects density and the buoyancy force determine whether objects will rise, sink, or stay neutrally buoyant.

Archimedes' Principle- the two forces that will determine if an object will sink or float are gravity (force pushing it down) and Buoyancy (the force that pushes the object up).

Standards: MS-PS2-2A Plan an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object.

Disciplinary Core Ideas PS2.A The motion of an object is determined by the sum of the forces acting on it; if the total force on an object is not zero, its motion will change. For any given object, a larger force causes a larger change in motion.

Materials:

For Cartesian Diver:

• a plastic bottle (between 0.5-1 liter)
• a graduated pipette
• a hex hut (that securely fits around the barrel)
• electrical tape to secure the hex nut if needed
• scissors
• enough water to fill the plastic bottle to the brim

For Swim Bladders:

• a small glass bottle
• balloon that fit inside the bottle
• plastic tubing (at least a 12 inches long)
• a big tub that is large enough for the glass bottle to float freely (ideally transparent)
• waterproof tape
• water
• towels (for clean-up)

Procedure:

For the Cartesian diver:

1. Snip off the bottom of the pipette (leaving at least 2 centimeters.
2. slide the hex nut over the remaining portion of the pipette. You may use electrical tape to secure it if needed.
3. Fill your plastic bottle to the very top with water
4. Using another small cup of water, fill the pipette with some water. Play around with the amount of water and test it's buoyancy in the cup. The pipette needs to barely float (meaning its slightly above surface level, but 90% underwater).
5. Keep it in the water till a bubble of air forms at the top.
6. Move it from the small cup and drop it into your large bottle.
7. Secure the bottle with its cap
8. Note: the Cartesian diver should float, if not you may have to take it our and adjust the water levels
9. Squeeze the bottle and watch the diver move down and back up to the top of the bottle.

For Fish Bladders

Assembly:

1. Push one end of the tube through the opening of the balloon.
2. When the tub is about 3/4 of the way in, use waterproof tape to tape them together. Make sure you are creating a tight seal.
3. Stick the balloon into the glass bottle
4. Tape the tube to the opening of the bottle.
5. Blow air into the other side of the tube to inflate the balloon.
6. Procedure:
7. fill your tub with water
8. Place the glass bottle inside the tub of water
9. using the other end of the tube, inflate the balloon to the desired amount (start slowly to allow the students to make observations and observe change.
10. inflate and deflate the balloon to explore the concept

Student prior knowledge: What prior concepts do students need to understand this activity?

Explanation:

First, the students will observe the Cartesian Diver to explore concepts of density and buoyancy. The Cartesian diver works because when the bottle is squeezed, the pressure exerted on the liquid inside the bottle increases.Remember the pipette had an air bubble before it was sealed in the bottle.

ince the pipette is in the water, the pressure on the pipette increases as well. This pressure is being exerted especially on the air bubble, confining it to a smaller space. The decrease in volume increases the density. Knowing that water is denser than air, when the pipette fills up with water, it becomes denser than the surrounding, causing it to sink. When you stop squeezing the sides of the bottle, the pressure on the pipette is also released, causing the air inside to push out the water. This allows more room for the air bubble to expand back to its original size.The Cartesian diver will now rise.

Next, students will oberve the fish bladder experiment and make observations. Fish have a thin-walled gas filled sac called a swim bladder.This demonstration represents the mechanics of a fish's swim bladder to help them stay buoyant.

The glass bottle represents the fish and the balloon represent its swim bladder. When the bottle is submerged in the bucket of water, it fills up with water and sinks to the bottom. When you inflate the balloon, it expands, pushing the water out of the bottle. This decreases the volume, and makes it float. This is due because their is a weaker downward push than the buoyancy force which is pushing it up.

Acording to the buoyancy force, their is an uowards force that pushes on an object that is immersed in water. The strength of this upward force is determined by the water displaced by it, or in other words, the object's volume. Thus the force of gravity and the upward force will determine if the object will sink or float.

Questions & Answers:

1.How is the Cartesian diver experiment releated to the swim bladder demonstration. What principle do they both show?

In order for fish to be buoyant, they must displace an equal or greater amount of water than its own body mass. The swim bladder expands and contracts depending on the amount of gas inside. Like the ballon expanding in the glass bottle, when the swim bladder expands, it increases its volume inside the fish's body and displaces more water. This causes the fish to float upwards because they are filled with more air, making them lighter. If the fish releases air, the swim bladder expands contracts, thus making the fish sink. When the fish fills up with air, the swim bladder expands and the fish rises.

When fish come up to the surface to "breathe", they are actually filling thier swim bladdders. Also, air is always being replenished through thier gills.

2. Salt water (ocean) fish have a swim bladder around 5% of thier body's volume while fresh water fish have swim bladders around 7% of thier body's volume. Consider what you know of the mechanics of swim bladders as well as the denisty of saltwater vs freshwater. What attributes to the differnce in size?

Salt water is denser than fresh water. Thus, when a fish displaces water in a salt-water environement, the weight of the displaced water is greater than if the fresh water fish we to do the same. Since there is already more force acting on the swim bladder from the water, the bladder doesn't have to work as hard as a fresh water fish which has not added force from the water.

3. Using these demonstrations, how is a SCUBA diver's equipment made?

Air regulators not only deliver oxygen to the divers, they also act as buoyancy control devices (BCD) which allow the SCUBA diver to sink, float or stay neutrally buoyant. Howrever, other factors also contribute to the diver's buoyancy such as the diver's denisty, the equipment's density, and the density of the sea water. The divers use a a BCD and an enflatable jacket. When the diver adds air, more water is displaced. From the demonstration of the glass bottle, we know that when the balloon inflates and displaces more water, the bottle floats. Same concept with the diver. When the diver adds more air they will also float up. When the divers use the BCD to remove air, the jacket compresses, thus allowing more water to enter. This will allow the diver to dive to a further depth.

Applications to Everyday Life:

1. Diving down to the bottom of a pool

In order to dive down to the bottom of a pool, we must release air by blowing out bubbles. This will release out the air to compress our lungs. This allows us to sink.

2. Scuba Diving

Scuba Divers must use a buoyancy control device which degulates the amount of air they release and breath in. They use this to control wheter they want to go to a lower or higher depth in the water.

3. Trying to submerge an inflatable beach ball to the bottom of a pool

If you have every tried to submerge an inflatable ball in water, you know it is a difficult task! Since air is less dense than water, the ball will remain buoyant unless air is released.

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