mass & density
DESCRIPTION
Mass & Density. Objectives. To explain what mass is To state the SI unit of mass as the kilogram To identify g and mg as smaller units for mass To measure the mass of an object using an electronic balance - PowerPoint PPT PresentationTRANSCRIPT
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Objectives• To explain what mass is• To state the SI unit of mass as the kilogram• To identify g and mg as smaller units for mass• To measure the mass of an object using an
electronic balance• To define density of a substance as its mass
per unit volume and state the SI unit for it• To investigate and describe how the density
of objects (floating and sinking) can be determined
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Objectives• To demonstrate the ability to calculate
density based on the formula(density = mass/volume) and use the approximate units (kg/m3 or g/cm3)
• To convert one form of units to another (g/cm3 to kg/m3)
• To solve problems using the density formula
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Mass
The mass of a substance is themeasure of the amount of matter in it.
It depends on the number and size of particles that make up that substance.
The mass of a body is the samewhenever it is measured.
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The SI unit for mass is the kilogram (kg).
Large masses are measured in tonnes while small masses are measured in grams (g) or milligrams (mg).
1 tonne = 1000 kg1 g = 1 10-3 kg = 1/1000 kg1 mg = 1 10-6 kg = 1/1000000 kg
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Measuring mass
A beam balance is used to givevery accurate measurements.
However, the electronicbalance is easy to handle.It gives highly accuratemeasurements and allows easy digital reading.
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Weight
Weight is the gravitational force acting on a body.
The weight of a body is greater on Earth than on the moon becausethe earth exerts a greatergravitational force on itthan the moon.
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Measuring weight
A compression balance and a spring balance can be used to give very accurate measurements.
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Density
A piece of iron has a greater mass than a piece of wood of the same volume. We say that iron has a higher density than wood.
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Definition of Density:The density of a substance is its mass per unit volume.
Mass
VolumeDensity =
SI unit for density is kg/m3.Another common unit for density is g/cm3
Formula:
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Example 1
Sharifah found a ring.
The ring has a mass of 38.6 g and a volume of 2 cm3. Calculate the density of the ring.
Is the ring made of pure gold?
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Example 2
Osmium, the densest metal found, has a density of 22.6 g/cm3. The mass of a block of osmium was found to be 113 g. Find its volume.
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Mass
VolumeDensity =
Finding the density of a substance
Step 1: Measure the mass and the volume ofthe substance
Step 2: Divide the mass of the substance by its volume.
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Finding the density of a liquid
Step 1: Measure the mass and thevolume of the substance
Mass
VolumeDensity =
Step 2:
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Finding the density of a regularly shaped object
Step 1: Measure the mass and calculate fromdimensions, the volume of the object
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Mass
VolumeDensity =
Step 2:
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Finding the density of an irregularly shaped object
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Finding the density of an irregularly shaped object
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Finding the density of an irregularly shaped object
Mass
VolumeDensity =
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Substance Density in g/cm3
Platinum 21.5Gold 19.3Lead 11.3Silver 10.5Copper 8.9Iron 7.9Zinc 7.1Aluminium 2.7Glass 2.5Ice 21.5Pinewood 19.3Cork 0.24
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Substance Density in g/cm3
Mercury 13.6Glycerine 1.3Sea water 1.03Pure water 1.00(at 4OC)Olive oil 0.92Turpentine 0.87Petrol 0.80Alcohol 0.79
Air 0.00129Hydrogen 0.00009
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(a) Which state of matter has the lowest density?Gas
(b) Which liquid has the highest density?Mercury
(c) Which on of the following states normallyhas the highest density - solid, liquid or gas?Solid
(d) Which solid with a mass of 1 kg has thesmallest volume?Platinum
(e) Which liquid with a volume of 1 cm3 has thelargest mass?Mercury
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Normally, substances become less dense when they are hotter. Hence, hot air is less dense than cold air. Do you know why?
For equal masses of air, the hot air has a bigger volume than cold air.
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Think!!!Think!!!
Think!!!Think!!!
Think!!!Think!!!
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Think!!!Think!!!
Think!!!Think!!!
Think!!!Think!!!
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Substances such as pebbles or ball bearings sink in water because they have a higher density than water.
Floating and sinking
Some substances float and some others sink.
A piece of cork or wood which is less dense than water will float.
In general, substances with lower densities will float in fluids (liquids and gases) of higher
densities.
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corn oil0.9 g cm-3
water1.0 g cm-3
glycerine1.3 g cm-3
cork0.24 g cm-3
ice0.92 g cm-3
glass2.5 g cm-3
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What happens to a solid placed in a liquid if the densities of the solid and the liquid are the same?
The solid will float in the liquid.
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References
Tho Lai Hong, Ho Peck Leng, Goh Ngoh Khang, (2001), Interactive Science 1, Pan Pacific Publications.
Chan Kim Fatt, Eric Y K Lam, Lam Peng Kwan, Loo Poh Lim, (2000), Science Adventure, Federal Publications.
Chuen Wee Hong, Lee Khee Boon, Hilda Tan, Ruth Chellappah, Koh Thiam Seng, Yap Kueh Chin, (2000), EPB.