FORCES AND ENERGY
Density
__________________
By Leonard Nungu
0788201361
leonard@wellspringacademy.org
9/23/2024 11:13 AM
Checkpoint science
1
MASS AND VOLUME
Iron nails
are heavy
Same volume of polystyrene food containers
are very light
2
EXPLANATION
▪ A large block of polystyrene has large mass than a
▪
small piece of metal
Food containers made of polystyrene are very light
because they are hollow (have spaces filled with air
inside)
▪ Also, these containers have very large volume and
small mass
▪ Contrary, iron nails are heavy due to their high mass
and small volume
3
DEFINITION OF DENSITY
●
4
CALCULATING DENSITY
●
5
FORMULA
TRIANGLE
6
VOLUME OF A REGULAR OBJECT
● Regular object has volume that can be calculated
using a simple equation, e.g., a cuboid, square,
cylinder etc.
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VOLUME OF A REGULAR OBJECT
● Volume = l x width x h
8
CALCULATING DENSITY
Workout the density for each substance giving the correct units.
9
SOLUTION
10
VOLUME OF AN IRREGULAR OBJECT
● Volume for such object is found by
displacement method.
11
VOLUME
OF AN
IRREGULAR
OBJECT
12
STEPS TO FIND VOLUME OF
AN IRREGULAR OBJECT
13
COMPARING DENSITIES OF MATERIALS
Material
Helium
0.00018
Air
0.0012
Wood
0.35-0.95
Water
1.0
Concrete
2.4
Aluminium
2.7
Osmium
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14
COMPARING DENSITIES OF MATERIALS
15
NEUTRONIUM
• an extremely dense phase of matter
composed primarily of neutrons.
• It is made up of neutrons only
• Found in collapsed stars
• Forces in collapsed star are too large that
atoms are compressed into very small
spaces
• A teaspoon of neutronium can weigh 500
million tonnes
16
FLOATING AND SINKING
1. If an object is denser than
water, it will sink in water.
2. However, if an object is less
dense than water, it will float
in water.
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OBJECTS USED IN SWIMMING POOLS
Have low density than water because they are
made of polystyrene and are hollow with only
air inside.
An example is a float.
18
OBJECTS USED IN SWIMMING POOLS
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OBJECTS USED IN SWIMMING POOLS
20
OBJECTS USED IN
SWIMMING POOLS
21
WHY DO SHIPS NOT SINK IN WATER?
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9/23/2024 11:13 AM
Checkpoint science
23
WHY DO SHIPS NOT SINK IN WATER?
• Because the average density of the
whole ship is less than the density of
water.
• A ship has large spaces filled only
with air in the lower deck making it
hollow hence easy to float.
• Density of ship changes when its
mass changes
24
LIQUIDS OF DIFFERENT DENSITY
25
LIQUIDS OF DIFFERENT DENSITY
•
•
•
•
When liquids of different densities are
mixed together carefully, the less dense
liquid floats on top.
If the liquids are immiscible, separate
layers are formed.
For example, when crude oils from oil
wells or ships spills out, it floats on the
water.
This causes water, air and land pollution
especially on the shores.
26
CRUDE OIL FLOATS ON WATER
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GASES AND LIQUIDS
•
•
•
•
Gases are less dense than liquids because
their particles are far apart than in a liquid.
This why the rain falls downward because
it is denser than air.
Fizzy drinks contain dissolved carbon
dioxide (0.002g/cm3) that escapes upwards
because its less dense than the drink which
is mostly water with density of 1.0g/cm3.
Bubbles rise to the top since they are
lighter than the liquid.
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GAS
BUBBLES
RISING
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GASES OF DIFFERENT DENSITIES
•
•
•
Helium is one of the least dense gases used
to fill balloons.
A balloon filled with helium will float in air
because the balloon and gas is less dense
than air.
Although, hydrogen is less dense than
helium it is not used to fill balloons as it
forms an explosive mixture with air.
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GASES OF DIFFERENT DENSITIES …
•
•
•
Gases are easily compressed allowing
more gas to occupy a small volume hence
increasing the density of the gas.
Density of gases decreases with increase in
temperature as particles expand increasing
volume at the same mass.
That is why hot air balloons can float in air
because the hot air inside the balloon is
less dense than the cold air outside.
31
WHY HOT AIR BALLOON FLY EARLY
MORNING/LATE EVENING?
•
•
There is a greater temperature difference
between hot air inside the balloon and the
outside providing more lift.
The air is more stable, providing a safer
flying experience
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