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Mass & Density

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

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Mass & Density

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  1. Mass & Density

  2. 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 massper unit volume and state the SI unit for it • To investigate and describe how the densityof objects (floating and sinking) can be determined

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. Measuring weight A compression balance and a spring balance can be used to give very accurate measurements.

  9. 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.

  10. Mass Volume Density = Definition of Density:The density of a substance is its mass per unit volume. Formula: SI unit for density is kg/m3.Another common unit for density is g/cm3

  11. 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?

  12. 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.

  13. Mass Volume Density = 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.

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

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

  16. Finding the density of an irregularly shaped object

  17. Finding the density of an irregularly shaped object

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

  19. 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 21.5 Pinewood 19.3 Cork 0.24 Solid

  20. Substance Density in g/cm3 Mercury 13.6 Glycerine 1.3 Sea water 1.03 Pure water 1.00(at 4OC) Olive oil 0.92 Turpentine 0.87 Petrol 0.80 Alcohol 0.79 Air 0.00129 Hydrogen 0.00009 Liquid Gas

  21. (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 normally has the highest density - solid, liquid or gas? Solid (d) Which solid with a mass of 1 kg has the smallest volume? Platinum (e) Which liquid with a volume of 1 cm3 has the largest mass? Mercury

  22. 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.

  23. Think!!! Think!!! Think!!!

  24. Think!!! Think!!! Think!!!

  25. Floating and sinking Some substances float and some others sink. Substances such as pebbles or ball bearings sink in water because they have a higher density than water. 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.

  26. cork0.24 g cm-3 ice0.92 g cm-3 corn oil0.9 g cm-3 water1.0 g cm-3 glass2.5 g cm-3 glycerine1.3 g cm-3

  27. 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.

  28. 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.

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