Density is a physical characteristic of every substanceDensity is a physical characteristic of every substance

Density is the mass of unit volumeDensity is the mass of unit volume

What Is Density?

What Is Density?

Density is a Density is a physical physical characteristic of characteristic of every substanceevery substance

Density is the Density is the Mass of Unit Mass of Unit VolumeVolume

What is Mass?

Mass is a measure of the quantity of matter

Mass is often confused with weight.

The mass of anything is constant but weight is effected by location. A person/object will weigh less on the moon or in space than on earth because of the difference in gravity.

Mass (the amount of matter) - blood, bones etc does not change. Weight changes because Weight = Mass x Gravity.

What is Volume?What is Volume?

Volume is the amount of space an object Volume is the amount of space an object occupiesoccupies

Volume is:Volume is:length length multiplied by multiplied by width width multiplied by multiplied by heightheight

or or l l X X w w X X hh

In each case, the distance is in cm and since it (cm) is multiplied In each case, the distance is in cm and since it (cm) is multiplied three times, this results get centimeters cubedthree times, this results get centimeters cubed

D equals Density D equals Density M equals Mass M equals Mass

V equals VolumeV equals Volume

• Density is mass divided by volume or

D= M/V

Density referred to as“mass per unit volume.”

• Mass is how much matter the object has

• Per simply means divided by

• Unit volume is a measure of how much space an object takes up

Calculating Density!

Take the mass and divide by its volume!

What Are the Units of Density?

• Mass units would include– Grams for very small objects or– Kilograms for larger objects

• Volume units would include– Centimeters cubed (cm)3 for small objects or– Meters cubed (m)3 for large objects– Millilitres for small amounts of liquids– Litres for larger amounts of liquid - Both units (mass and volume) are included in answer for measuring density - Grams/Centimeter cubed or g/cm3

An Example?

A block of woodL = 10 cmH = 4 cmW = 2 cmMass= 160 grams

Use the information provided to calculate the density of the object

Density = Mass/VolumeDensity = Mass/Volume

Mass = 160gMass = 160g Volume = 10cm x 4cm x 2cm = 80cm3Volume = 10cm x 4cm x 2cm = 80cm3

Density = Mass/VolumeDensity = Mass/Volume

Density = 160/80 = 2g/cm3Density = 160/80 = 2g/cm3

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Irregularly Shaped Objects

• To find the density of an irregularly shaped object -

• If the length, width, and height of the object, are not uniform e.g. a stone, you cannot use l X w X h to determine volume.

Irregularly Shaped Objects

• Start with a graduated cylinder of water filled about half full• Record the volume of water in the cylinder• Drop in the irregularly shaped object• Record the volume of water in the cylinder with the object in it• Subtract the original volume from the secondvolume to determine the volume of the object

• You are measuring the amount of water displaced by the object which is equal to the volume of that object

• This is called:volume by displacement•Handy!!

Liquids

• A liquid can be weighed to determine its mass.

• To do this, measure a cylinder in grams and record its empty mass• Add the liquid• Now weigh the cylinder again• Subtract the mass of just the cylinder and this gives the mass of the liquid

Liquids

• To determine the volume, simply look atwhere the liquid measures in the cylinder and record the amount

Some Specific Densities :

Substance Density (g/cm 3)

Gold 19. 3

Mercury 13. 5

Lead 11. 3

Aluminum 2. 7

Water (liquid) 1. 0

Water (ice) 0. 92

Air 0. 0013

WWHY DO SOME HY DO SOME THINGSTHINGS

FLOAT WHILE FLOAT WHILE OTHERS SINK?OTHERS SINK?

Ever Notice…

• When you put ice into water it floats tothe top

Why?• Ice is less dense than water by just a little bit. That is why your ice floats to the top of water.

Sink or Float?

• Solids can float or sink in a liquid.

List examples of solids which would sink in water?

• Any solid will sink in water if it has adensity greater than the density of water.

• Water has a density of 1g/ cm 3

Any solid with a density greater than 1g/ cm 3 will sink in water!Any solid with a density less then water will float in water !

Can you explain how?Can you explain how?

Large ships can float on water?Large ships can float on water? A submarine can submerge into the ocean A submarine can submerge into the ocean

depths?depths? A hot air balloon floats into the sky?A hot air balloon floats into the sky?

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Further food for thought on density Further food for thought on density visit:visit:

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