Bobbers+&+Archimedes'+Principle

__ Bobbers, Buoyant Force and Archimedes’ Principle __

In this activity you will investigate what makes objects float or sink, such as ships and submarines. You will learn about buoyancy.

Objects float if they are less dense than the fluid they are submerged in. Objects sink if they are denser than the fluid they are in. Objects with the same density as the fluid they are in are neutral in buoyancy. Determining whether an object will float or sink is done by comparing densities.

In fluids, pressure increase with depth due to gravity. This results in a difference between the pressure at the top and bottom of a submerged object. Due to the increasing pressure with depth, the force on the lower half of the object is greater than the force on the upper half of the object. Thus, the net force due to increasing pressure is in the upward direction, creating the buoyant force. The buoyant force acts in the direction opposite to the force of gravity.

Archimedes’ Principle tells how strong the buoyant force is on an object. The buoyant force on a submerged object will equal the mass of the fluid displaced by the object (Archimedes' Principle). This means that the mass of a floating object will equal the mass of fluid it displaces. In other words, the mass of a floating object will equal the buoyant force acting on it.

Archimedes’ Principle can be tested using a floating container. This is because the mass of a floating object will equal the mass of the displaced fluid. This means for a floating object, Mass = (Density of the fluid) x Volume. This can be rearrange to Density = Mass /Volume. With this equation we can test, Archimedes’ Principle. The mass of a floating object divided by the submerged volume should always equal the density of the fluid. (For floating object, only the submerged volume matters.)

Data Table . Procedure: 1. Measure the mass of the cylindrical container. 2. Measure the mass of the container with the smaller mass inside it. 3. Measure the diameter of the container 4. Determine the radius of the cylindrical container 5. Measure the submerged length of the floating, cylindrical container 6. Calculate the submerged volume of the cylindrical container. 7. Calculate the density of the container using its mass and its submerged volume. 8. Repeat steps 1 through 6 with the larger mass inside of the container. Analysis: 1. When will an object float in a fluid? 2. How can whether an object will float or sink be determined? 3. Explain how the net forces on a submerged object results in a buoyant force? 4. What is Archimedes’ Principle? 5. How does the mass of a floating object compare to the buoyant force acting on it? 6. Calculate the volume of the whole cylindrical container. Now calculate if the cylindrical container would float if its mass were doubled. (With mass 1 inside it) 7. Calculate the maximum mass the container will float?
 * ** Archimedes’ Principle ** || ** Container **
 * & Mass 1 ** || ** Container **
 * & Mass 2 ** ||
 * ** Mass of Container & Weight ** ||  ||   ||
 * ** Diameter of Container ** ||  ||   ||
 * ** Radius of Container ** ||  ||   ||
 * ** Submerged **** Length ** ||  ||   ||
 * ** Submerged Volume ** ||  ||   ||
 * ** Density of the Floating Container ** ||  ||   ||

. http://ed.ted.com/lessons/the-real-story-behind-archimedes-eureka-armand-d-angour

Demonstration: A change in pressure causes the amount of displaced fluid to change. This change in volume causes a change in density. Changes in density causes floating and sinking. Mass doesn't change. http://physicalsciencecottrell.wikispaces.com/Cartesian+Diver+Submarine



__ Hot Air Balloons __ Video: http://pbskids.org/dragonflytv/show/balloon.html (Project: Hair dryer and Mylar bag)

Hot air balloons are based on a very basic scientific principle: warmer air rises in cooler air. Essentially, hot air is less dense than cool air, because it has less mass per unit of volume. A cubic foot of air weighs roughly 28 grams (about an ounce). If you heat that air by 100 degrees F, it weighs about 7 grams less. Therefore, each cubic foot of air contained in a hot air balloon can lift about 7 grams. That's not much, and this is why hot air balloons are so huge -- to lift 1,000 pounds, you need about 65,000 cubic feet of hot air.

Air density of the atmosphere.

Air density inside and outside the balloon.

Explanation: http://www.schooltube.com/video/e22fc6e8af893c849306/Buoyancy-of-A-Hot-Air-Balloon http://www.knowmia.com/watch/lesson/32865