Buoyancy and Density 14-2

Buoyant Force Buoyant force = upward force that keeps an object immersed in or floating on a liquid It ’ s the force that pushes an ice cube up to the surface of water Buoyant force = upward force that keeps an object immersed in or floating on a liquid It ’ s the force that pushes an ice cube up to the surface of water

Buoyant Force and Fluid Pressure Water exerts pressure all around an object Horizontally the pressures are equal and cancel each other out. Vertically, the deeper the object, the more pressure exerted The force pushing upward is the buoyant force Water exerts pressure all around an object Horizontally the pressures are equal and cancel each other out. Vertically, the deeper the object, the more pressure exerted The force pushing upward is the buoyant force

Determining Buoyant Force Archimedes was a mathematician who lived in 3rd century BCE and discovered a way to determine buoyant force. Archimedes's Principle = buoyant force is equal to the weight of the volume of fluid the object displaces Archimedes was a mathematician who lived in 3rd century BCE and discovered a way to determine buoyant force. Archimedes's Principle = buoyant force is equal to the weight of the volume of fluid the object displaces

Cont …. So … –1st determine amount of liquid displaced –2nd determine how much that liquid weighs –3rd weight = buoyant force So … –1st determine amount of liquid displaced –2nd determine how much that liquid weighs –3rd weight = buoyant force

Weight vs Buoyant Force Object will sink if its weight is greater than the buoyant force acting on it Object will float if weight is equal to buoyant force Buoying Up = object under water is pushed up until the part under is equal to the amount it displaces Object will sink if its weight is greater than the buoyant force acting on it Object will float if weight is equal to buoyant force Buoying Up = object under water is pushed up until the part under is equal to the amount it displaces

Density and Floating Object is more dense than its surroundings = sink Object is less dense than surroundings = float Object is more dense than its surroundings = sink Object is less dense than surroundings = float

Math Focus! Page 415 Complete 1, 2,3 on your paper 1.D = 25g ÷ 20cm 3 1.D = 1.25 g/cm 3 2.D = 546g ÷ 420cm 3 1.D = 1.3 g/cm 3 3.D = 163g ÷ 50cm 3 1.D = 3.26 g/cm 3 Complete 1, 2,3 on your paper 1.D = 25g ÷ 20cm 3 1.D = 1.25 g/cm 3 2.D = 546g ÷ 420cm 3 1.D = 1.3 g/cm 3 3.D = 163g ÷ 50cm 3 1.D = 3.26 g/cm 3

Determining Density Need mass and volume! Volume of a regular solid = L*W*H –(length*width*height) Volume of irregular solid = use displacement. –Measure volume of liquid, add object, measure new volume, subtract to get volume of object. Need mass and volume! Volume of a regular solid = L*W*H –(length*width*height) Volume of irregular solid = use displacement. –Measure volume of liquid, add object, measure new volume, subtract to get volume of object.

Changing Overall Density 1.Changing shape can change density- see page Changing mass (ex.submarine) 3.Changing volume (ex. Swim bladder) 1.Changing shape can change density- see page Changing mass (ex.submarine) 3.Changing volume (ex. Swim bladder)