Fluids Part 2 A look at mass, volume, weight, buoyancy and density Mr. Williams Grade 8 Science

Weight, Mass and Volume Would you be able to weight the same on the moon as you would on Earth? Would you weigh more or less…why? The force of gravity is not as strong on the moon as it is on Earth Weight- is the measure of how strongly gravity pulls on you. Therefore your weight is dependent on where you are being measured.

Weight, Mass and Volume Cont’d Mass – Is a measure of the amount of matter that is within a substance or object. So if you were to take a trip to the moon… Would your mass change? Would your mass and weight change? Would your weight only change? Would neither change?

Weight, Mass and Volume Cont’d So, here is a question. What has a greater mass? A kilogram of gold or a kilogram of polystyrene foam? Since mass measures the amount of matter in a substance, their mass is the same. However, you need a lot more foam than gold to make a kilogram, therefore the volume of the foam will be larger. Volume – Is a measure of how much space an object occupies. You can find the volume of a solid by multiplying its three dimensions together: Volume = length x width x height - The units of measurement for volume are always in cubic units (m3, cm3 and so on)

Volume and Equal Relationships The basic unit of measuring volumes is the litre. Lets look at the example below: A container that is 10cm x 10cm x 10cm holds 1000cm3 or 1 litre (L) of water. Since a litre is also equal to 1000mL we find that 1cm3 is equal to 1mL

Volume and Displacement So, from the last slide we were able to figure out volume because the object was a regular shape, but what happens when the shape of the object is irregular. This can be done by measuring displacement Displace – to take the place of

Density Density is the term used for the mass-to-volume ratio in science and technology, so, basically… Density – a measure of the mass per unit volume of a substance. Think back to when we used the example of the gold and the polystyrene foam. The gold has a greater density because there are far more gold particles in a given volume than the polystyrene foam.

Density Cont’d The particle theory can be used to explain density. Density depends on two things: 1. The mass of the particles 2. How closely the particles are packed together Since the particles of solids are more tightly packed together than liquids and gases, solids are often denser than liquids and gases.

Density Cont’d Density is also affected by the type of particles a substance is made of. For example, oil and water are both liquids, but water is much denser. Density is considered to be a characteristic property of matter. A characteristic property is one that is specific to a particular substance and can be used to distinguish one material from another. Density can be determined using the following equation: Density = mass / volume The units of measurement for density of solids and liquids are g/mL or g/cm3, and for gasses kg/m3

Density and the Wonder of Water Water behaves differently than other fluids when the temperature changes. Warmer water will rise to the top of a lake or stream because it is less dense. However, as the temperature drops below 4°C, the water becomes less dense again. Hence why ice floats on top of water. Water is the most dense at 4°C and water freezes at 0°C If water behaved the same way as other liquids, our lakes would freeze solid in the winter from the bottom up, killing all the plants and animals in that habitat.

Molecular Structure of Water

Water Cont’d…