A boat floating can be greatly appreciated, especially if you are in the boat at the time. But what keeps a boat from sinking? Physics can explain these concepts. There are many forces that act on a sailing ship to put it in motion, but the buoyant force is what is required to keep the boat from sinking. A buoyant force is the normal force that pushes up on the boat supporting its weight in a fluid. The buoyant force "equals the weight of the fluid displaced by the object."(pg.427, Serway and Jewett) This concept is Archimede's Principle.
The pressure on an object in a fluid varies with the depth of that part of the object in the fluid.
B=(P b – P t)A = (ρ fluidgh)A = ρ fluidgV
B=Buoyant force
P b=pressure at bottom
P t=pressure at top
A=area of bottom face
ρ fluid=fluid density
g=gravity
h= height
V=volume of fluid displaced by object
(formula from pg. 428, Serway and Jewett)
"The fraction of the volume of a floating object that is below the fluid surface is equal to the ratio of the density of the object to that of the fluid."(p.429, Serway and Jewett)
V fluid/Vobj = ρ obj/ρ fluid
Vobj=volume of the object
ρ obj=density of the object
Buoyancy of the craft is created by the shape of the hull, but also with buoyant materials in specific places. Air tanks, buoyancy bags, and polystyrene blocks are all used to add buoyancy to a boat.
The figure below shows how the buoyant material should be distributed and the effects if it is not.
figure from The Handbook of Sailing
The distrubution of buoyancy is key to having the boat float properly.
Bernoulli's principle is that the air moving past a foil, an object that has one curved side and one flat side, will take longer to move past the curved side than the flat side of the foil. This will cause the flat side to have higher air pressure and to exert a force on the object. The force cause a planes wing to lift and a sail to push a boat. "With the wind pushing on one side of the sails and the water pushing on the other side of the centerboard, the boat moves forward." (p. 35, Dellenbaugh)
The angle at which sailing is important. A 45 degree angle to the wind is the most effective angle.
Wind is what propels a sailing ship so weather has a large impact on the craft. Certain weather conditions are not suitable for sailing or specific crafts.
Sink or Float Introduction: I am doing this experiment to find the density of aluminum foil to see if it floats or sinks when placed in water. I hope to find out how the density of aluminum foil changes when weight is added to the foil. I hypothesize that the boat will hold 20 pennies before sinking. You will need to get: Aluminum foil Pennies Water And a big container or tub for your boat to float in. Procedure: 1.
As the propeller rotates (fig 3-1) it forces water down and back as this is happening water must move into the void created by the spiraling blades. This creates a pressure differential across the blade- Low pressure on the back side and high pressure on the front side. This causes water to be sucked into the propeller and accelerated out the back (fig 3-3) much like a house-hold fan (fig 3-2). This action creates the thrust that drives a boat.
How much is your boat able to hold? A boat can only hold so much weight before it starts to sink. Too much weight on a boat can cause the boat to sway back and forth or roll over. It is very important to make sure that the load of your cargo is balanced or the chance of capsizing a boat is greatly increased.
Before running the test, the depth of the overlaying water inside each core was adjusted to 12.7 cm (5 in). The grid was also adjusted such that the lower surface was 5.08 cm (2 in) above the sediment surface (the grid oscillated between 5.08 and 7.62 cm above the interface).
Bernoulli’s principle is the concept that as the speed of a moving fluid (liquid or gas) increases, the pressure within that fluid decreases. This principle was originally formulated in 1738 by the Swiss mathematician and physicist Daniel Bernoulli, it states that the total energy in a steadily flowing ...
Drag is a major contributor to how an object travels through fluid/air. Drag is caused by the disrupted air immediately behind an object moving through fluid/air. It acts perpendicular to and in the opposite direction of travel of the object and impedes the motion of the object. It would make sense that if the drag is minimized the object will travel farther.
Flight is one of the most important achievements of mankind. We owe this achievement to the invention of the airfoil and understanding the physics that allow it to lift enormous weights into the sky.
waves. The waves at the front of the boat are compressed and are shorter than the longer, spread out waves at the back of the boat.
http://search.ebscohost.com/login.aspx?direct=true&db=mih&AN=5537767&site=ehost-live>. Judd, Alan, and Martin Hovland. 11.5 Gas-induced Buoyancy Loss." Seabed Fluid Flow: The Impact of Geology, Biology and the Marine Environment. Cambridge:
No known methods for calculating factors such as stability, stiffness, and sailing characteristics of ships Methods of calculating the center of gravity, the heeling characteristics, and stability factors for sailing ships were unknown. As a consequence, ships’ captains had to learn the operational characteristics of their ships by trial-and-error testing. Vasa was the most spectacular, but certainly not the only, ship to sink by heeling over during the 17th and 18th centuries. Measurements taken and calculations performed since 1961 indicate that the Vasa was so unstable it would have heeled over at a list of 10 degrees; it could not have withstood the wind gust of 8 knots that caused the ship to capsize (8 knots -- about 9 mph -- being the estimated speed of the gust that caused the Vasa to sink) [2].
Ocean currents are horizontal or vertical movement of both surface and deep water throughout the world’s oceans (Briney, n.d.). The primary generating forces are wind and differences in water density caused by variations in temperature and salinity. Currents generated by these forces are modified by factors such as the depth of the water, ocean floor topography and deflection by the rotation of the Earth. Horizontal currents are wind driven, fast moving and carries small amount of water; while, vertical currents are slow moving, density driven and carries large bodies of water. In this paper I will describe horizontal and vertical currents, their importance and some of the tools used to measure ocean currents.
The trials and tribulations of flight have had their ups and downs over the course of history. From the many who failed to the few that conquered; the thought of flight has always astonished us all. The Wright brothers were the first to sustain flight and therefore are credited with the invention of the airplane. John Allen who wrote Aerodynamics: The Science of Air in Motion says, “The Wright Brothers were the supreme example of their time of men gifted with practical skill, theoretical knowledge and insight” (6). As we all know, the airplane has had thousands of designs since then, but for the most part the physics of flight has remained the same. As you can see, the failures that occurred while trying to fly only prove that flight is truly remarkable.
On a more scientific note I am interested in mechanics of fluids. This interest was enforced last year when I had the opportunity to attend a lecture on fluid mechanics at P&G. At the conference I greatly expanded my knowledge regarding the physical aspect of fluids and their properties. In last year's AS course we have met a topic in this field. I will be applying ideas and knowledge gathered from last year for this investigation.
Surface Tension: The contractive tendency of a liquid that allows it to resist an external force. This is measured in Newton.