# Density is a physical characteristic of every substance Density is the mass of unit volume What Is Density?

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Density is a physical characteristic of every substance Density is the mass of unit volume What Is Density?

 Density is a physical characteristic of every substance  Density is the Mass of Unit Volume

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?  Volume is the amount of space an object occupies Volume is: length multiplied by width multiplied by height or or l X w X h In each case, the distance is in cm and since it (cm) is multiplied three times, this results get centimeters cubed

D equals Density M equals Mass V 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 wood L = 10 cm H = 4 cm W = 2 cm Mass= 160 grams Use the information provided to calculate the density of the object

Density = Mass/Volume  Mass = 160g  Volume = 10cm x 4cm x 2cm = 80cm3  Density = Mass/Volume  Density = 160/80 = 2g/cm3 Further activities on measuring density visit:  juniorscience.ie juniorscience.ie

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 second volume 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 at where the liquid measures in the cylinder and record the amount

Some Specific Densities : SubstanceDensity (g/cm 3) Gold19. 3 Mercury13. 5 Lead11. 3 Aluminum2. 7 Water (liquid)1. 0 Water (ice)0. 92 Air0. 0013

W HY DO SOME THINGS FLOAT WHILE OTHERS SINK?

Ever Notice… When you put ice into water it floats to the 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 a density 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?  Large ships can float on water?  A submarine can submerge into the ocean depths?  A hot air balloon floats into the sky?  For explanation visit: juniorscience.ie juniorscience.ie

Further food for thought on density visit: www.juniorscience.ie www.juniorscience.ie

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