Presentation on theme: "Chapter 11 – Forces in Fluids"— Presentation transcript:
1 Chapter 11 – Forces in Fluids Section 2 – Floating and SinkingStandards8.c – Students know that buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced8.d – Students know how to predict whether an object will float or sink
2 Density Density – mass per unit volume Density = mass / volume (g/ml or g/cm3)The density of water is 1.0 g/ml or 1.0 g/cm3
3 DensityAn object that is more dense than the fluid in which it is immersed sinksAn object that is less dense than the fluid in which it is immersed floats
4 Density PracticeA sample of liquid has a mass of 24 g and a volume of 16 mL. What is its density? Does the liquid sink or float?Density = mass / volumeDenisty = 24 g / 16 mLDensity = 1.5 g/mLDenisty is greater than 1.0 g/mL so it sinks
5 Calculating DensityPractice ProblemA piece of metal has a mass of 43.5 g and a volume of 15 cm3. What is its density?Density = mass / volume Density = 43.5 g / 15 cm3Denisity = 2.9 g/ cm3
6 Densities of Substances By comparing densities, you can predict whether an object will sink in a fluid0.70 g/cm3 = wood0.92 g/cm3 = corn oil0.93 g/cm3 = plastic1.00 g/cm3 = water1.02 g/cm3 = tar1.26 g/cm3 = glycerin1.34 g/cm3 = rubber1.38 g/cm3 = corn syrup8.80 g/cm3 = copper13.6 g/cm3 = mercury
7 DensityChanges in density cause a submarine to dive, rise, or float.
8 DensityChanges in density cause a submarine to dive, rise, or float.
9 DensityChanges in density cause a submarine to dive, rise, or float.
10 BuoyancyThe buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighterBuoyant Force – upward force exerted by a fluid on a submerged object
11 BuoyancyThe greater pressure at greater depths means the net force is greatest pushing upward on a submerged object
12 BuoyancyArchimedes’ principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces
13 Floating and SinkingIf the weight of the object is greater than the buoyant force – then the net force will be downward and the object will sinkIf the weight of the object is less than the buoyant force then the net force will be upward and the object will float
14 Buoyancy and DensityAn object with greater volume has a greater buoyant force acting on it – even if the object is more dense than the fluid it is immersed inDensity of iron lead is 11.3 g/ml and cork is 0.25 g/ml – lead sinks, cork floats