DENSITY Grade 8 Science

Density, Volume and Mass Density is the relationship between an object’s volume and its mass. Describes the crowdedness of atoms. The more squished together atoms are, the more dense the substance will be. Unique for every substance!

Volume & Mass Volume is the amount of space the object occupies, Mass is the amount of matter in a substance, often measured with a balance scale (sort of like weight) Weight is not the same as mass! Weight is the force of gravity on an object

Density and Temperature As a substance is heated, it’s particles spread out therefore lowering its density. Place each state in order from LEAST dense to MOST dense: Solid Gas Liquid LEAST DENSE Have more space between atoms; Are LESS dense than liquid - The attractive forces between atoms is not strong enough to stop solids from pushing them apart. - LESS dense than solids, but MORE dense than liquids MOST DENSE Do not have a lot of space between atoms; The most dense of all the sates

The equation for density Density is the mass of a substance divided by its volume: Solids = grams/cubic centimeters  Liquids = grams/milliliters Formula to determine the volume of a rectangular solid: Length x Width x Height

Volume and Density Question: What is the density of an object with a mass of 10 g and volume of 2 cm3? Answer:

Complete the Density Worksheet  Try It! Complete the Density Worksheet 

DENSITY POP QUIZ Calculate the density of a block of wood measuring 5cm x 10cm x 12 cm. The mass of this block is 45g. (/6) Knowing that the density of water is 1.0g/cm3, would this block of wood sink or float in water? (/1) (note* points are given for the equationS used to Calculate BOTH volume & density, PLUS answers given with correct units!!) /7

Buoyancy Buoyancy is the tendency for materials to sink or float in a liquid The upward force exerted on objects in a fluid is called buoyant force.

Floating occurs when an object does not fall or sink Buoyancy Continued… Floating occurs when an object does not fall or sink The atoms of the fluid exert a force in the opposite direction of gravity

Buoyancy Continued The shape of an object can create an average density that is less than the fluid it is submerged in EXAMPLE: A steel boat can float on water even though steel is more dense than water. What is AVERAGE DENSITY? The total mass of an object divided by its total volume

Buoyancy in Fish? The air bladder in fish contains a mixture of air and water The fish’s depth in the water depends on how much air is inside the sac. The more water in the sac the lower the fish sinks. The more air in the sac the higher the fish rises. This is how a submarine works underwater!

Archimedes http://ed.ted.com/lessons/mark-salata-how-taking-a-bath-led-to-archimedes-principle

Archimedes Archimedes used water displacement to determine the volume of the kings crown, then he weighed it to find the mass. The volume of water displaced would be equal to the volume of the crown.

Calculating the Density of Irregularly Shaped Objects If an object floats in water, we can immediately conclude that it is less dense than the water. If we measure the volume of water displaced by the object when it is placed into the container of water, we can calculate the weight of the object, because its weight will be equal to the weight of the water it displaces.

Example Density = ? Mass = 25.5 g Volume = 18 – 5 = 13 mL Density = m / V Density = ?

YOUR CHALLENGE: Using Archimedes Principle: Calculate the density of a marble Calculate the density of your pen or pencil

Neutral Buoyancy He also found that if the mass of an object is lighter than the volume of water it displaces then it will float. When gravity = buoyancy, it is known as neutral buoyancy. Force of Gravity = Buoyant Force

In your notes, answer the following I CAN statements I CAN write the formula for VOLUME (rectangular object):_________ I CAN write the formula for DENSITY:__________ I CAN give the units of measurement for density in a LIQUID:_____ I CAN give the units of measurement for density in a SOLID:_____ I CAN identify this force - the upward force exerted on objects submerged in a fluid:________________ I CAN identify the following definition: this occurs when an object does not fall in or sink in water, but remains suspended in the fluid:________________ I CAN explain how objects that would otherwise sink (ex. Large Ships), are able to float (1 sentence please) I CAN rank Solids, Liquids and Gases in order of density from the LEAST dense to the MOST dense: ________, ________, ________