Buoyancy and Pressure Science 8 Ms. Deanne

Particle Model All matter is made of tiny particles The particles are always moving Some particles are attracted or bonded to other particles All particles have space between them Solids have little space Liquids have more space Gases have lots of space

Get up and Move! Demonstrating the Particle Model

Particle Model and Density As temperature INCREASES, density DECREASES. This is because the particles gain energy, start to move faster and spread out more= less particles in a given area. This is why a hot air balloon rises when the flame heats the air inside. The air inside becomes less dense than the heavier cooler air outside and so the balloon is held up by this cooler air.

Particle Model  In general matter becomes more dense as it changes state from a gas liquid solid. The particle spaces decrease. This is not the case for water which actually decreases its density as it turns to ice- the particles arrange themselves in an irregular spread out pattern making ice less dense than water.

Sink or Float? Complete the Sink or Float Activity Sheet

Buoyancy BUOYANCY: the tendency of an object to float when placed in a fluid (cork, wood) BUOYANT FORCE: the upward force exerted on objects (n) (glycerol, mercury) BUOYANCY and DENSITY are related. The more dense an object is the greater its buoyant force will be. More particles = greater ability to hold up objects.

Cartesian Divers Need: Water Bottle Straw Piece (2-3cm) (Top of Bendy Straw, We’ll use the rest for a different experiment) Clay Follow steps in Video - https://www.youtube.com/watch?v=Gqmc_OFBy_g Why does the “diver” move up and down?

How things Work http://www.edumedia-sciences.com/en/media/630-submarine How does a Submarine work?

Buoyancy and Density Shape is important in determining if something will float or sink-if the objects weight is spread over a large enough area it will float, even if the object has a higher density than the liquid it is in. Boats float because their shape displaces a lot of water and they have large amounts of air spaces. This makes their AVERAGE DENSITY less than water.

Think about It Which doughnut will float the best? A Timbit or an Apple Fritter?

Buoyancy in Fish  Fish have swim bladders to regulate their average density, allowing them to float or sink by filling the bladder with air or expelling it.

Archimedes Principle A scientist was faced with the problem of determining if the Kings crown was made of pure gold as the jeweller stated, or if it was mixed with other metals https://www.youtube.com/watch?v=0v86Yk14rf8 Weigh the crown. Get an equal weight of pure gold bar Submerge crown in water and collect overflow-measure volume Do the same for the pure gold bar If the crown was pure gold its density should be the same and it should displace the exact same amount of water as the gold bar---it didn’t and the jeweller was beheaded for his dishonesty..

Archimedes Principle The buoyant force on an object has to be equal to the amount of water it displaces. https://www.youtube.com/watch?v=0v86Yk14rf8

COMPRESSION IN FLUIDS Compressibility: ability to decrease in volume. Gases are compressible because there are spaces between the particles. Solids and liquids are incompressible as the spaces between the particles are already close- creates a lot of pressure when force is applied .

Compression in Fluids Compression is useful in tires and air bags when we want absorption Incompressibility is useful in hydraulic and pneumatic presses.

Compressing Fluids Compression of Fluids Activity Use a Pipette to move the following substances 10mL air 10mL Water 10mL Body Wash What do you Observe? Which one is easiest to move?

Pressure in Fluids – Pascal’s Law Pressure: amount of force applied to a given area-acts in all directions Pressure is affected by FORCE and AREA. The greater the force, the greater the pressure. The smaller the area, the greater the pressure.

P F A Pressure = Force * Area F= force (N) P= pressure (N*m2 or N*cm2 ) Or Pa (Pascals) A= area (m2 or cm2 ) P F A

Practice Questions A forestry worker accidentally strikes a pipe with the end of a pickaxe while trying to dig a hole. If the pickaxe strikes with a force of 2000 N and the end of the pickaxe measures 0.02 m by 0.01 m, how much pressure is exerted on the pipe by the pickaxe?

Practice Questions A swordfish jumps out of the water and the tip of its pointy upper jaw strikes a wooden wall of a fishing boat with 7500 N of force. If the tip of the pointy jaw has an area of 0.0004 m2 , what pressure is placed on the part of the wooden wall that is struck by the jaw?

Pressure Calculations Complete Pressure Calculations Practice Complete Pressure Calculations Assignment

Atmospheric Pressure Scuba Divers: The greater the depth the greater the pressure. There is a lot of pressure at the bottom of the ocean floor. There are more particles pushing down from above. Atmospheric pressure: as you go higher into the atmosphere the pressure deceases-less particles pushing down on top of you. We do not feel the air pressure down here at sea level because there is an equal and opposite force inside the body. Measured by a Barometer. More pressure inside then outside (airplane) =ears will pop More pressure outside than inside (deep dive) = ears will cave

Pascal’s Law Pascal’s Law: an enclosed fluid transmits pressure equally in all directions led to discovery of : Hydraulic devices: use a liquid in an enclosed system to transmit pressure from one area to another. http://www.edumedia-sciences.com/en/media/442-hydraulic-lift Pneumatic devices: uses air-safer than most liquids

Bernouli’s Principle Bernoulli’s Principle: Objects move from an area of HIGH to LOW pressure- always!! Fast moving particles create LOW pressure. Slow moving particles create HIGH pressure…

Hydraulic Pressure Uses two pistons of different sizes to create pressure in the system and exert a force on the object. Read pages 78-82 in your Textbook and answer the questions on page 84, #1-4

Unit Project Fluids in the News Project