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Buoyancy Pre Lab Reading

Last updated over 2 years ago
5 questions
Scuba diving is a mode of underwater diving where the diver carry their own source of breathing gas, usually compressed air, allowing them greater freedom of movement than surface-supplied divers, and longer underwater endurance than breath-hold divers. Expert divers have set records exploring ocean depths of approximately 1000 feet (305 meters), but most scuba divers swim closer to shore where the water is shallower. Scuba diving is an excellent way for underwater scientists to study the oceans and the organisms that live there.

Scuba diving requires training as well as specialized equipment, called SCUBA (Self-Contained Underwater Breathing Apparatus) gear, which includes one or two oxygen tanks strapped to the back of the diver and a regulator that fits into the mouth and controls the flow of air.  It is essential for divers to be able to breathe underwater, but they also need to be neutrally buoyant to prevent floating to the surface or sinking to the bottom. What makes divers sink or float depends on a combination of the density of their bodies, the density of the diving equipment they wear, and the density of sea water.
1

What is Scuba diving?

1

What are the two advantages of scuba diving?

1

What does SCUBA stand for?

Water has a natural force that pushes up towards the surface.  This is called the buoyant force. The buoyant force comes from the pressure exerted on the object by the water. Pressure increases as depth increases, so the pressure on the bottom of an object is always greater than the force on the top resulting in a net upward force.

The net upward buoyancy force is equal to the weight of water displaced by an object. This force enables an object to float or at least seem lighter. If the weight or density of an object is less than the weight or density of the displaced water when fully submerged, this results in the object tending to rise. This is called Positive Buoyancy. Some natural things that have positive buoyancy are ducks, people, Sargassum seaweed, and air bubbles all float on/to the surface. Some man-made this that float are boats, buoys, some types of plastic trash. If the object has exactly the same density as the water, then its buoyancy equals its weight and the object will remain submerged in the water, but will neither sink nor float; they are suspended or move in the water column. This is called Neutral Buoyancy. Things that have the ability to float suspended in the water column are plankton, both zoo plankton and phytoplankton and some man-made plastic and Styrofoam trash. Natural things that have the ability to move or swim in the water column are nekton such as fish, sharks, whales, seals, and squid. Man-made things that can move in the water column are scuba divers, submarines and some plastic trash like plastic bags. An object with a higher density than the water will sink. This is called Negative Buoyancy. Some living things that are benthic (found on the ocean floor) are sand dollars, crabs, clams, corals, sponges and sea urchins. Man-made things that sink are ship wrecks and some types of metal trash.

Other forces act on a floating body in the ocean, such as drag (friction due to the density of the fluid) which slows an object down, thrust (the force as the body pushes the water away) which speeds an object up, and weight (body’s affect due to gravity) which pushes the body down toward the ocean floor.

The net weight of a scuba diver can be altered by decreasing or increasing density using air or solid weights. Scuba divers can change their density by adding or releasing air from a buoyancy compensator, or BC, a vest that holds air.  Also, by adding or removing solid weights in their weight belts, scuba divers change their net weight and buoyancy.


The density of fresh water is 1 g/cm³.  The density of saltwater depends upon the amount of salt dissolved in the water. Cold water can dissolve more salt than warm water, making it more dense. Therefore, the physical releasing air from a buoyancy compensator, or BC, a vest that holds air.  Also, by adding or removing solid weights in their weight belts, scuba divers change their net weight and buoyancy.
3

The four forces exerted on a scuba diver are weight, thrust, drag and buoyant force. Drag the boxes that best describes the cause of these force and what it does to the object in the water (2 in each box)

  • Comes from the pressure exerted on the object by the fluid
  • Friction due to the density of the fluid
  • Slows an object down
  • Speeds an object up
  • Body’s affect due to gravity
  • Pushing up
  • The force as the body pushes the water away
  • Pushes the body down
  • Weight
  • Thrust
  • Drag
  • Buoyant Force
3

Drag the boxes that best describes negative, neutral and positive buoyancy.

  • Some plastic and styrofoam trash are man-made exeamples
  • Ducks, people, sargassum and seaweed are natural examples
  • Zoo plankton and phytoplankton are some natural examples.
  • Objects are suspended or move in the water column
  • Ship wrecks and some types of metal trash are some man-made examples.
  • Objects sink.
  • Boats, buoys, some types of plastic trash are some man made examples.
  • Sand dollars, crabs, clams, corals, sponges and sea urchins are some natural examples
  • Objects float.
  • Negative Buoyancy
  • Neutral Buoyancy
  • Positive Buoyancy