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Density

Density. Remember that density is the mass of one cubic centimetre (or cubic metre) of a substance. So for example, gold has a density of 19.3 g/cm 3 . This means one cubic centimetre (cm 3 ) of gold has a mass of 19.3 grams (or one cubic metre of gold has a mass of 19300 kg).

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Density

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  1. Density Remember that density is the mass of one cubic centimetre (or cubic metre) of a substance. So for example, gold has a density of 19.3 g/cm3. This means one cubic centimetre (cm3) of gold has a mass of 19.3 grams (or one cubic metre of gold has a mass of 19300 kg)

  2. Can you copy this please! kg/m3 kg Density (g/cm3) = mass(g) volume(cm3) Or using the formula triangle; m D x V m3

  3. Density of regular shapes volume = length x width x height density = mass/volume mass using a scale height width length http://www.youtube.com/watch?gl=IE&feature=related&hl=en-GB&v=14nahP_FVnM

  4. Precision and Accuracy • Precise – High number of significent figures. Repeated measurements are similar • Accurate – Near to the “real” value Can you copy this please?

  5. Density of liquids Volume Mass of liquid Mass of cylinder Mass of liquid and cylinder Density = mass/volume

  6. mass Density of irregular shapes (1) Difference in level gives the volume of the shape Density = mass/volume

  7. mass Density of irregular shapes (2) Displacement can volume of object Density = mass/volume

  8. Pressure F N P A Pressure = Force Area x Can you copy this please? N/m2 or Pa m2

  9. An example A woman of weight 600N has a total shoe area of 150 cm2 and a man of weight 750 N has a total shoe area of 360 cm2. What is the pressure beneath their feet? Angelina pressure = force/area = 600/150 = 4 N/cm2 Brad pressure = force/area = 750/360 = 2.1 N/cm2

  10. The pressure acts in all directions • Copy!

  11. Pressure and depth Pressure increases with depth (P = ρgh) The pressure acts in all directions

  12. Pressure difference between top and bottom = ρgh = 1000 kg/m3x9.8x0.2 = 1960 N/m2 0.2m

  13. Draw these sentences! • The particles in a solid are close packed. • The particles in a solid are in regular positions vibrating around a fixed point. • The particles in a liquid are also close packed. • The particles in a liquid also vibrate and move around randomly. • The particles in a gas are far apart. • The particles in a gas are moving very quickly. • For the same substance (e.g. water), the particles are the same size in the solid, liquid or gaseous forms. • Mr Porter is the world’s best science teacher.

  14. Solids • Fixed shape • Cannot flow • Difficult to compress • Generally dense

  15. Liquids • Shape can change • Can flow • Not easy to compress • Generally dense

  16. Gases • Shape can change • Can flow • Easy to compress • Low density

  17. Changes of state

  18. Brownian motion – Fat droplets in milk Brownian Motion Einstein's Explanation of Brownian Motion http://www.practicalphysics.org/fileLibrary/wmv/brownian_motion.wmv

  19. Brownian motion is the seemingly random movement of particles suspended in a fluid (i.e. a liquid or gas). It is due to the instantaneous imbalance in the combined forces exerted by collisions of the particle with the much smaller liquid molecules surrounding it.

  20. Pressure in a gas Collisions of the gas particles with the side of a container give rise to a force, which averaged of billions of collisions per second macroscopically is measured as the pressure of the gas

  21. PHET! • http://phet.colorado.edu/en/simulation/gas-properties

  22. Pressure versus temperature (at constant volume)

  23. P/T = constant • P1/T1 = P2/T2 The temperature MUST be in kelvin This is only true for a constant mass of gas at constant volume.

  24. At -273°C, P = 0!!

  25. Absolute/Kelvin temperature and Celsius T (in Kelvin) = T (in degrees Celcius) + 273

  26. Kelvin Temperature The kelvin Temperature is proportional to the average kinetic energy of the particles in a substance. Note that they are not all travelling at the same speed.

  27. Temperature The hotter the temperature, the faster the average speed of the particles Note that they are not all travelling at the same speed.

  28. pV = constant • p1V1 = p2V2 (at constant temp) This is only true for a constant mass of gas at constant temperature.

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