Chapter 3 Section 3 Floating and Sinking
Bell Ringer • How is it possible that a huge ship can float easily in water under certain conditions? Yet in a few hours the ship could be a sunken wreck. • What makes objects float?
Buoyancy • An object feels lighter under water because of an upward force called Buoyancy. • The buoyant force acts in an upward direction against the forces of gravity, so it makes an object feel lighter. • Since the pressure in a fluid increases with depth, the upward pressure on the bottom of the object is greater than the downward pressure on the top. (See figure 13 pg. 91)
Buoyancy (cont.) • What type of force is acting upward on the submerged object. Net Force • A submerged object displaces, or takes the place of, a volume of fluid equal to it’s own volume.
Time for a Video!!!! • Brain Pop | Buoyancy
Archimedes’ Principle • Relates the amount of fluid a submerged object displaces to the buoyant force of an object. • This relationship is named after its discoverer Archimedes. • Archimedes’ Principle states that the buoyant force on an object is equal to the weight of the fluid displaced by the object.
Buoyancy Demonstration • Which one of the film containers has neutral buoyancy? Neither • Which one of the film containers has negative buoyancy? #3 • Which one of the film containers has positive buoyancy? #2
Calculating Volume • How can I find the volume of container #3? Measure the amount of water that spilled into the other container.
Floating and Sinking • Remember that there is always a downward force on a submerged object. What is causing this Force? The object’s own weight. • Objects that have a weight greater than the buoyant force will sink.
Density • What is Density? • The density of a substance is its mass per unit volume. • To calculate the density of a substance, what two properties of the substance do you need to know? Mass and Volume • The equation for Density is Density= _Mass_ Volume
Density • An object that is more dense than the fluid in which it is immersed sinks. • An object that is less dense than the fluid in which it is immersed floats to the surface. • If the density of an object is equal to the density of the fluid which it is immersed, the object neither rises nor sinks in the fluid. Instead it floats at a constant level
Densities in Substances • Objects as well as other liquids can float on one another. • Changing the density of an object can make it float or sink in a given fluid.
Buoyancy and Density • Another way of changing density is to change the volume. • A ship floats because it is not a solid block of steel and the hull of the ship contains a large volume of air. • The bigger the object the larger the buoyant force is because more fluid is displaced. • The shape of a ship causes it to displace a greater volume of water than a solid piece of steel causing it to float.