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Mass, Weight and Density

Mass, Weight and Density. By: Mrs Rachel Chan – Lim. MASS AND DENSITY. Question. Have you ever wondered why a test-tube containing a certain volume of mercury feels much heavier than a test-tube containing an equal volume of water?. Density.

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Mass, Weight and Density

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  1. Mass, Weight and Density By: Mrs Rachel Chan – Lim

  2. MASS AND DENSITY Density

  3. Question • Have you ever wondered why a test-tube containing a certain volume of mercury feels much heavier than a test-tube containing an equal volume of water? Density

  4. Density • When we compare masses of equal volumes of different substances, we are actually comparing densities Density

  5. Mass • What is Mass? • It’s the measure of the amount of matter in a body. • SI Unit: kilogram (kg) • Instruments to measure mass: Beam balance Density Electronic balance

  6. Volume • What is Volume? • It’s the measure of the amount of space a matter takes up. • SI Unit: cubic metre (m3) Density

  7. Which items will float on water ??? Density

  8. Density • It actually means how much stuff (mass) we can fit into a space (volume). • Example: • The more students (mass) we pack into a class (volume), the denser it would be. • The less students (mass) we pack into a class (volume), the less dense it would be. • Density can be calculated from a ratio of mass over volume • Equation is : Density = Mass/Volume • SI unit: kg/m3 Density

  9. Density of various materials Mercury : 13570 kg/m3 Iron : 7874 kg/m3 Glass : 2600 kg/m3 Rubber : 1100 kg/m3 Water : 997 kg/m3 1000 kg/m3 Ice : 900 kg/m3 Air : 1.225 kg/m3 Source : http://www.allmeasures.com/Formulae/static/materials/ More likely to float Density

  10. Density – Basic Calculation • Let’s say a ball is 2 m3 in size. This would describe the volume. • After weighing it on an electronic scale, it appeared that its mass is 100 kg. • The density will then be : mass/volume • = 100 kg / 2 m3 = 50 kg/m3 • Through conversion, {(50 x 1000) g / (100)3 cm3}; it can also be described as 0.050 g/cm3 Density

  11. Work Example • Example 1: A block of concrete 0.4 m long, 0.3 m wide and 0.1 m high has a density of 2500 kg/m3. Calculate its mass. Density

  12. Solution Solution to example 1: Given length, breadth and height of concrete block. Volume of concrete block = l x b x h = (0.4 m)(0.3 m)(0.1 m) = 0.012 m3 From D = M / V , M = D x V = 2500 kg/m3 x 0.012 m3 = 30 kg Density

  13. Try Yourself! Example 2: A 50 cm3 glass flask is filled with oxygen and weighed. The mass is found to be 50.72 g. By means of a vacuum pump, the gas is then removed and the glass flask reweighed. The new mass is found to be 50.00 g. Calculate the density of oxygen in (a) g/cm3 (b) kg/m3. Density

  14. Solution Solution to example 2: Mass of empty glass flash and oxygen, m1 = 50.72 g Mass of empty flask, m2 = 50.00 g Volume of glass flask, V = 500 cm3 Mass of oxygen, m = m1 – m2 = 0.72 g From D = M / V , density of oxygen = (0.72) g / 500 cm3 = 1.44 x 10-3 g/cm3 Density

  15. Solution Solution to example 2: (b) Density of oxygen in kg/m3 = [(1.44 x 10-3) x 10 -3 ]kg / [1 x 10-6] m3 = 1.44 kg/m3 Density

  16. Facts about Milk http://hypertextbook.com/facts/2002/AliciaNoelleJones.shtml Density

  17. Ice = Water?? If ice is frozen water, then why does it float on water? How is ice different from water? Let’s use Using Density = Mass/Vol When water is frozen into ice in a fridge, Qn: Did the density change and why? Qn: Did the mass change and why? Qn: Did the volume change ? Qn: In what way has the volume changed and how did it come about? Density

  18. MASS AND WEIGHT Density

  19. What happens if I were to drop a book now? • Why does it act like that?

  20. Weight

  21. Weight • Conversion from mass to weight: • 1 kg = 10 N • So what is your weight? • What is Weight? • It’s the measure of the amount of gravitational pull acting on a body. • SI Unit: Newton (N) • Instruments to measure weight: Compression spring balance Extension spring balance

  22. Compression spring balance Electronic balance • Differences between Mass & Weight On Earth

  23. Differences between Mass & Weight On Moon

  24. Differences between Mass & Weight • Mass – is the same as long as the amount • of matter inside is the same • Weight – it will change depending on the • pull of gravity acting on it. • e.g. (gravity)earth > (gravity)moon • (object mass)earth = (object mass)moon • (object weight)earth > (object weight)moon

  25. The End

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