Mass and Density Have Fun !!! Before we start, please mark your attendance at the end of the lesson. Do spend about 2 hour on this lesson. Do note that I will not be covering this topic in class anymore. This topic will be tested in Term 2 test. Have Fun !!!

Mass What is mass? Mass - the amount of matter in a substance depends on the number and size of particles making up that substance the same wherever it is measured

What is the SI unit of mass? SI unit for mass – the kilogram (kg) Large masses (e.g. a car) - measured in tonnes 1 tonne = 1 000 kg Small masses (e.g. a watch) – measured in grams (g) 1 gram (g) = 0.001 kg

Instruments for Measuring Mass A beam balance - gives very accurate measurements An electronic balance - easier to use - gives more accurate measurements - gives digital readings

Weight What is weight? Weight - the gravitational force acting on a body The weight of a body is greater on Earth than on the moon. Why? The earth exerts a greater gravitational force on it than the moon.

An extension spring balance A compression spring balance Measuring weight An extension spring balance A compression spring balance

What is the SI unit of weight? SI unit for weight - the newton (N) A body of mass 1 kg has a weight of about 10 N. Hence an apple of mass 100 g will have a weight of about 1 N

In science, such statements are not accurate Why? We sometimes hear people saying that expanded polystyrene is lighter than wood or that water is heavier than oil or that aluminium is lighter than iron. In science, such statements are not accurate Why? There is no mention of the volume of the materials being compared.

We can correctly say iron is heavier than aluminium, expanded polystyrene is lighter than wood or that water is heavier than oil only when comparing equal volume of them.

In science, the term ‘density’ is used. Iron has a greater mass than an equal volume of aluminium and so we say ‘Iron is denser than aluminium.’ Expanded polystyrene has a smaller mass than an equal volume of wood and so we say ‘Expanded polystyrene is less dense than wood.’

Density 1 cm3 of aluminium has a mass of 2.7 g, so we say the density of aluminium is 2.7 g/cm3. 1 m3 of air has a mass of 1.29 kg, so we say the density of air is 1.29 kg/m3.

Definition of Density: The density of a substance is its mass per unit volume. Formula: Mass Volume Density = SI unit for density is the kilogram per cubic metre (kg/m3). Another common unit for density is the gram per cubic centimetre (g/cm3).

Finding the density of a substance Step 1: Measure the mass and the volume of the substance Step 2: Divide the mass of the substance by its volume. Mass Volume Density =

Finding the density of a liquid Step 1: Measure the mass and the volume of the substance Mass Volume Density = Step 2:

Finding the density of a regularly shaped object Step 1: Measure the mass and calculate from dimensions, the volume of the object l h b r Mass Volume Density = Step 2:

Finding the density of an irregularly shaped object

Finding the density of an irregularly shaped object

Finding the density of an irregularly shaped object Mass Volume Density =

Solid Substance Density in g/cm3 Platinum 21.5 Gold 19.3 Lead 11.3 Silver 10.5 Copper 8.9 Iron 7.9 Zinc 7.1 Aluminium 2.7 Glass 2.5 Ice 0.92 Pinewood 0.50 Cork 0.24 Solid

Liquid Gas Substance Density in g/cm3 Mercury 13.6 Glycerine 1.26 Sea water 1.03 Pure water 1.00 (at 4OC) Olive oil 0.92 Turpentine 0.87 Petrol 0.80 Alcohol 0.79 Air 0.001 29 Hydrogen 0.000 09 Liquid Gas

Substances, e.g. a piece of metal or a volume of gas become less dense when they are hotter. Why is this so? They expand when they become hotter. With a bigger volume, their densities decrease, since density is mass per unit volume.

Density of ice is 0.92 g/cm3. Density of sea water is 1.03 g/cm3. Hence ice is less dense than water and so it floats.

Some objects float and some others sink. Floating and sinking Some objects float and some others sink. Objects such as pebbles or ball bearings sink in water because they have a higher density/are denser than water. A piece of cork or wood will float on water because it has a lower density/is less dense than water.

cork 0.24 g/cm3 olive oil 0.92 g/cm3 wood 0.65 g/cm3 water 1.0 g/cm3 glycerine 1.3 g/cm3 aluminium 2.5 g/cm3

The solid will be freely suspended in the liquid. What will happen to a solid when immersed in a liquid of the same density? The solid will be freely suspended in the liquid.

Visit the following websites to learn about 1. How a submarine can either float or sink depending on changes in its density http://science.howstuffworks.com/submarine1.htm 2. How a hot air balloon works – has to do with density again http://science.howstuffworks.com/hot-air-balloon.htm

Watch the following video and complete worksheet 1:

Try this experiment from your home Please see file with the name “Egg Experiment”

Finally…. Complete worksheet 2 and hand in on the first day of your lesson when you come back from your E-learning lessons. Do remember to mark your attendance and click on “submit” after filling in your details.