Topic 3.3 – Density, Temperature and Buoyancy Mix and Flow of Matter
Rainbow Colors Why did the different substances sit on top of one another? Each liquid had a different density The greater densities sank to the bottom.
Review We learned that viscosity changes with temperature…. RIGHT? Does Density change with temperature too??? https://www.youtube.com/watch?v=yAgtFL_Vp5E LET’S FIND OUT TOGETHER!
Hydrometers A hydrometer is a device used for measuring the density of liquids
Imagine…. Close your eyes and imagine swimming in a lake on a HOT SUMMER DAY. Is the temperature of the water the same on the surface as it is when you stretch your legs straight down?
The warm water will float on top of the cold water Warm water has a lower density that cold water! COOOOL!
The Particle Model The particle model can explain this change in density! WOO! Particles in a substance move faster when they are heated up This makes the spaces between the particles larger
THIS AFFECTS THE DENSITY OF THE SUBSTANCE!!! When the spaces get larger between the particles, this increases the volume BUT the number of particles stay the same SOOOO…. Warmer liquids will have a lower density!
Solids Liquids, Liquids, LIQUIDS… that’s all we EVER talk about! What about solids? Does the same rules apply to solids?
We saw today that solids (coke can and diet coke can) either sink or float. Do other solids float? https://www.youtube.com/watch?v=4wyPPljNdK8 We know others sink… like when you were using displacement to find the density of metal pieces….
Buoyant Force Why do some objects float while others sink? When an object is in a liquid, the force of gravity will pull it down. BUT The liquid has an opposite force called The Buoyant Force
Floaters… Objects will float when: 1. The density of the object is LESS THAN the density of the liquid 2. The buoyant force of the liquid on the object is GREATER than the force of gravity pulling it down.
Sinkers… Objects will sink when: 1. The density of the object is GREATER than the density of the liquid 2. The force of the gravity acting on the object is GREATER than the buoyant force of the liquid
BUOYANCY Buoyancy is the tendency of an object to float when placed in a fluid. Buoyant force is the force in fluids that act against gravity.
Divers A diver is able to move down not only because of the gravity force but because of his kicking Kicking is greater than the buoyancy force
A diver is able to move upward because of the buoyant force Along with the force of kicking This is greater than the gravitational force of gravity
A diver can float suspended in the water Because the force of gravity and the buoyant force are equal
Plimsoll Lines We know that densities of salt water and fresh water are VERY different… Can this cause a problem for ships that transport heavy items to a from different places?
Ships… As a ship sails from the Atlantic Ocean (salt water) to the St. Lawrence River (fresh water) it SINKS VERY LOW! WHY? It sinks because fresh water is less dense than salt water
On the sides of ships are Plimsoll Lines It shows how heavily a ship can be loaded in different water conditions.
WNA = winter north Atlantic W = winter salt water S = summer salt water T = tropical salt water F = Fresh water TP = Tropical fresh water https://www.youtube.com/watch?v=xniW3_afO-0