Book+1+3.3

Book 1 3.3

3.3

III. Floating and Sinking A. Buoyant Force 1.Water exerts a force that acts on a submerged object 2. Buoyant force in the upward direction, against the force of gravity, so it makes an object feel lighter. 3.Pressure on a fluid increases with depth, the upward pressure on the bottom of the object is greater than the downward pressure on the top. The result is a net force acting upward on the submerged object. 4. Submerged object displaces a volume of a fluid equal to its own volume. i. it displaces a volume of fluid equal to the portion of the object that is submerged. ii. Archimedes' Principle - relates to the amount of fluid a submerged object displaces to the buoyant force on the object. a.) Greek mathematician b.) The buoyant force on an object is equal to the weight of the fluid displaced by the object. B. 1. There is always a downward force on a submerged object. i. The force is the weight of the object. ii. Object will SINK if the weight of the object is greater than buoyant force. iii. Object will BEGIN TO SINK if the weight of the object is less than the buoyant force. It will only sink deep enough to displace volume of the fluid with weight equal to its own - stops sinking then iv. If weight of an object is exactly equal to the buoyant force, the two forces are balanced. C. Density - of a substance is its mass per unit volume 1. Density = mass/volume 2. An object that is more dense than the fluid in which it is immersed sinks 3. An object that is less dense than the fluid in which it is immersed floats to the surface 4. If an object's density of the fluid it is immersed in, the object neither rises nor sinks in the fluid. it floats at a constant level. 5. Air is a fluid (gases are fluids) i. Objects float in air if their density is less than the density of the air. 6. Can change density is to change its volume. i. A large object displaces more fluid than a small one ii. Object with grater volume has a greater buoyant force acting on it - even its weights are equal. iii. Greater volume displaces = greater buoyant force
 * For an object to float in water it must displace its own weight in the water.
 * Objects float higher in salt water because each drop of salt water weighs more - you have to move less of it to = the objects weight

Quiz 3.3

1. The buoyant force of water pushes up against gravity and makes the object feel lighter. 2. According to Archimedes' Principle, the weight of water displace by the object is = to the weight of the object. Water weighs 1g/ cm3, so the object must weigh 10 grams. 3. greater 4. less 5. equal to 6. The buoyant force of an object is = to the weight of the fluid displaced by the object 7. Density is the mass of an object per unit volume. 8. A force acting on an object in a fluid is in the opposite direction to gravity

Study Guide 7. Acts in an upward direction 8. it causes a net force 10. density 11. sink 18. false - Archimedes' 24. buoyant force 25. greater 26. corn oil 30. Archimedes' principle states that the buoyant force on an object equals the weight of the fluid displaces by the object. The block in A is only partially submerged, block b is submerged. Block B displaces more fluid than A. Since fluids are the same the buoyant force in A is less than the buoyant force in B.