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Density
Remember that density is the mass of onecubic centimetre (or cubic metre) of a
substance.
So for example, gold has a density of19.3
g/cm3
. This means one cubic centimetre(cm3) of gold has a mass of 19.3 grams (orone cubic metre of gold has a mass of19300 kg)
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Density (g/cm3) = mass(g)
volume(cm3)
Or using the formula triangle:
m
D x V
kg/m3
kg
m3
Can you
copy this
please!
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Density of regular shapes
volume = length x width x height
density = mass/volume
mass using a scale
length
width
height
http://www.youtube.com/watch?gl=IE&feature=related&hl=en-
GB&v=14nahP_FVnM
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Precision and Accuracy
PreciseHigh number of significent
figures. Repeated measurements are similar
AccurateNear to the real value
Can you copythis please?
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Density of liquids
Mass of liquid and
cylinder
Mass of cylinder
Mass of liquid
Density = mass/volume
Volume
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Density of irregular shapes (1)
Difference in
level gives the
volume of the
shape mass
Density = mass/volume
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Density of irregular shapes (2)
Displacement can
volume of object
mass
Density = mass/volume
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Pressure
Pressure = Force
AreaN/m2 or Pa
N
m2
F
AP x
Can youcopy this
please?
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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
cm
2
. 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
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The pressure acts in all directions
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Pressure and depth
Pressure increases with
depth (P = gh)
The pressure acts in all
directions
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Pressure difference between
top and bottom
= gh
= 1000 kg/m3x9.8x0.2
= 1960 N/m
2
0.2
m
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Draw these sentences!1. The particles in a solid are close packed.
2. The particles in a solid are in regular positions
vibrating around a fixed point.
3. The particles in a liquid are also close packed.
4. The particles in a liquid also vibrate and move
around randomly.
5. The particles in a gas are far apart.
6. The particles in a gas are moving very quickly.
7. For the same substance (e.g. water), the particles are the same size
in the solid, liquid or gaseous forms.
8. Mr Porter is the worlds best science teacher.
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Solids
Fixed shape
Cannot flow
Difficult to compress
Generally dense
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Liquids
Shape can change
Can flow
Not easy to compress
Generally dense
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Gases
Shape can change
Can flow
Easy to compress
Low density
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Changes of state
.
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Brownian motionFat droplets in milk
.
Einstein's Explanation ofBrownian Motion http://www.practicalph
Brownian
Motion
http://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/brownian/brownian.htmlhttp://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/brownian/brownian.htmlhttp://www.practicalphysics.org/fileLibrary/wmv/brownian_motion.wmvhttp://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=24http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=24http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=24http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=24http://www.practicalphysics.org/fileLibrary/wmv/brownian_motion.wmvhttp://www.practicalphysics.org/fileLibrary/wmv/brownian_motion.wmvhttp://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/brownian/brownian.htmlhttp://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/brownian/brownian.html8/3/2019 Unit-5 Solids, Liquids and Gases (PowerPoint)
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.
Brownian motion is the seemingly random
movement of particles suspended in a fluid
(i.e. a liquid or gas). It is due to theinstantaneous imbalance in the combined
forces exerted by collisions of the particle
with the much smaller liquid moleculessurrounding it.
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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 secondmacroscopically is measured as the pressure
of the gas
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PHET!
http://phet.colorado.edu/en/simulation/gas-
properties
http://phet.colorado.edu/sims/ideal-gas/gas-properties_en.jnlphttp://phet.colorado.edu/sims/ideal-gas/gas-properties_en.jnlphttp://phet.colorado.edu/sims/ideal-gas/gas-properties_en.jnlphttp://phet.colorado.edu/sims/ideal-gas/gas-properties_en.jnlphttp://phet.colorado.edu/sims/ideal-gas/gas-properties_en.jnlp8/3/2019 Unit-5 Solids, Liquids and Gases (PowerPoint)
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Pressure versus temperature (at
constant volume)
.
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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.
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At -273C, P = 0!!
.
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.
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Absolute/Kelvin temperature and
Celsius
T (in Kelvin) = T (in degrees Celcius) + 273
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Kelvin Temperature
The kelvin Temperature is proportional to
the average kinetic energy of the particles in
a substance.
Note that they are
not all travellingat the same
speed.
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Temperature
The hotter the temperature, the faster the
average speed of the particles
Note that they are
not all travellingat the same
speed.
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pV = constant
p1V1 = p2V2 (at constant temp)
This is only true for a
constant mass of gas
at constant
temperature.
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