Density and Buoyancy Changes in Density We know

Density and Buoyancy

Changes in Density �We know as temperature increases, density decreases. �Why?

Changes in Density �We know as temperature decreases, density increases. �Why?

Example: Hot Air Balloon

Buoyancy �Buoyant Force: is the upward force on objects submerged in or floating on liquids

Floating �Gravity + Buoyant Force = no movement (rest) �Example: Boat

Sinking �Gravity + Buoyant Force = Downward Motion �Example: Rock

Rising �Gravity + Buoyant Force = Upward Motion �Example: Hot Air Balloon

Archimede’s Principle �The Buoyant Force is equal to the weight of the displaced water

Salt Water vs. Fresh Water �Salt Water D= 1. 03 g/m. L �Fresh Water D= 1. 00 g/m. L �Therefore, mass of 1 L salt water > mass of 1 L fresh water This means: �The larger the mass, the larger the buoyant force acting on an object submersed in the fluid �Salt water can support more weight per volume and it is easier to float

The Dead Sea – 31% salinity �The Dead Sea in Jordan is 9 times saltier than all oceans on the planet

Average Density �When items are made up of different substances it can be hard to know exact densities, so instead average densities can be used Average Density = total mass of all substances total volume Example: Pencil D = mwood+mrubber+mlead+maluminum volume �This is why objects that you think would normally sink are able to float

Ships �Hollow hulls

Life Jackets �Made with low density materials �Decreases a person’s average density therefore they float

Submarines �Use the flow of water to change the density of the submarine �When the weight = buoyant force floats �When the weight > buoyant force sinks

Key Ideas Object average density < fluid density FLOAT Object average density > fluid density SINK Object average density = fluid density BUOYANT * “fluid” can refer to a liquid or gas NEUTRALLY

Assignment: �Watch the “Density and Buoyancy” Video posted on the class Science page �Write a response to the 3 questions at the end of the video in your notebook