9.1 Ideas of
DENSITY
Learning objectives:
- Define mass, pressure and
density
- Explain if an object will float or
sink depending on its density
- Explain why solids, liquids and
gasses have a different density
Why these object/substances can arrange
themselves in different layers?
What do you notice? What is the same
and what is different?
Which one is heavier?
What is MASS?
What do you notice? What is the same
and what is different?
Which one is heavier?
What is
VOLUME?
So, what are the
physical quantities
that could affect
density?
What is
DENSITY?
PRATICAL – Comparing materials
Put them in order of density from
the lightest to the heavier then
write your observations in the
book
Use the material and metal box kit
Can you match each substance with the
right density?
DENSITY
0.94
11.3
0.93
0.85
0.79
19.3
2.7
1.0
0.0013
What is denser? A solid a liquid or a
gas? Why
9.2 Measuring
DENSITY
Learning objectives:
- Use the formula of density in reallife situations
- Describe how to measure the
density of a regular object
- Describe how to measure the
density of a irregular object
What is their density?
Their mass is
10 Kg and 1 kg
Which one is heavier?
PRATICAL 1 – Measuring the
density of different materials
Each group use some of the
regular blocks in the metal and
material box kit to measure the
density of different materials
How can we measure the density of an
irregular objet?
PRATICAL 2 – Measuring the density
of different materials
Use a digital scale and a measuring
cylinder to calculate the density of
different objects. Then write the full
method and calculations
9.3 DENSITY
calculations
Learning objectives:
- Use the formula of density tp
solve mathematical problems
- Describe how to measure the
density of a gas
Complete the
following
working sheet
0.8 m
0.8 m
0.2 m
0.8 m
0.2 m
A wooden cube has a
mass of 307.2 g and a
density of 0.6 g/cm3.
Find the length of the
cube
A butter block weights
200 g and has a density of
0.83 g/cm^3. Calculate
the volume.
0.2 m
2400 x
0.768=
1843.2 kg
11.5 x (5x5x3) = 862.5
862.5 g = 0.8625 Kg
19 (3.14 x 3^2) = 536.94
0.384
0.256
0.128
A wooden cube has a mass of
307.2 g and a density of 0.6 g/cm3.
Find the length of the cube
25 / 2 = 50
11.5 x 40 = 460 g
307.2 /0.6 = 512
512 = 8 cm
A butter block weights
200 g and has a density of
0.83 g/cm^3. Calculate
the volume.
200 / 0.83 = 240.96
1000 / 200 = 5
8.5 / 588 = 4998 g = 5 Kg
DEMO – Activity 9.3
Measuring the
density of a gas (air)
9.4 Pressure
9.5 Pressure
calculations
Learning objectives:
- Explain what is pressure including
the the factors that affects it
- Solve problems about pressure
What happen when you walk on a sand
beach?
Why do you leave
footprints?
What is pressure?
A force that pushes on a
surface
DEMO:
Can you penetrate the wall with a
finger?
Can you penetrate the wall with a pin
instead?
Why a drawing pin is
designed with a sharp point
and a broad head?
What can we say about the factors
that affect pressure?
Surface area and force
What is the formula for pressure?
P = F /A
What is the SI unit for pressure?
P = N/m2 = Pascal (Pa)
Problem:
What is the pressure if
N = 8 and A = 4 cm2?
P = F (N)/A
P = 8 N/ 4
2
m
2
(m )
=2
2
N/m
Problem: which of these four stumps exert
the greatest pressure?
Stump A: F=20N, A=2cm2 ; p = 10 N/cm2
Stump B: F=30N, A=2.5cm2 ; p =12 N/cm2
Stump C: F=45N, A=3cm2 ; p = 15 N/cm2
Stump D: F=16N, A=1cm2 ; p = 16 N/cm2
D force is the smallest but exert the
greatest pressure because concentrated in
a smaller area
W/S: 9L1 Pressure
PRACTICAL:
Who exerts the greatest pressure in
the class by standing on one foot?
Write your prediction, and then test it.
What do you need to do?
1 Measure the area of your foot without
considering the broken squares
2 Measure the mass and find the F = m x g
3 Use the formula of pressure to calculate
your pressure
The surface area of a one of these snow shoes is
ten times the size of a foot. Why is it easier to
wear those to walk in snow? Use the
calculations from the previous activity to
explain your answer.
What F is produced if a pressure of
1000 N/m2 act on A of 200000 cm2
(20 m2 x 1000 N/m2 = 20000 N)
Find A if the a F of 700 N create a
pressure of 70 N/m2
(700 N / 70 N/m2 = 10 m2)
W/S: 9L1 Interpreting
results
W/S: 9La/3 Pressure
points
9.6 Pressure in
gases and
liquids
Learning objectives:
- Describe what creates pressure in
a liquid
- Describe how hydraulic machines
work
- Explain the difference in
compressing a liquid or a gas
- Describe what creates pressure in
fluids at the molecular level
DEMO 1:
Tank with three holes
DEMO 2:
Cork in water:
Why is the cork
floating?
Thanks to an upward force (from water)
called upthrust and because it’s density is
lower and water density
W/S: 9L2 Pressure all
around
Pressure at the surface = 1 ATM
What is the pressure at 50m considering
that it increases by 1 ATM after every 10m?
Pressure at -50 m = 6 ATM
DEMO 3:
Compress a bottle filled with water
Is water easily compressible?
What happen when pressure is applied
to the liquid?
The liquid will push back with the
same force, pushing on the
container
Is the pressure the same at every point
in the liquid? Yes
Demo 4: Hydraulic machines
(transmitting pressure via syringes)
– Write your observations
W/S: 9Lb/3 A
question of pressure
Which one has more pressure why?
DEMO 5: Compress a bottle filled with air
Is air more compressible than water? Why?
Because air molecules are much further apart
with lot of empty space in between that is
easier to be compressed
DEMO 6: Fill up a balloon
Why is the balloon increasing in size?
When pressure is applied to a gas, it pushes
back with equal and opposite pressure. The
pressure of the gas is created by the gas
molecules as they collide with and rebound
from the container
W/S: 9Lb/4
Atmospheric
pressure
W/S: 9Lb/2 Pressure
effects
9.7 The turning
effect of a
force
Learning objectives:
- State what is a laver
and describe its utilisation
referring to different examples
- Explain the difference between a
force-magnifier and a
distance-magnifier
- State how can you measure the
weight of an object with a balance
scale
Moments
– theimages
turningare
effect
of a force
What these
showing?
The external
force applied
allows
a rotation
During
these actions
an external
force
(effort) is
applied.
How does
it affect
the the
movement
about
a fulcrum
(pivot),
making
object to
produced?
turn in the direction
of the force applied
What is a lever?
Simple machine that
decreases the force needed
to do a job
Can you think of some
examples about levers?
What
A longer
can belever
donecan
to increase
be used to
theincrease
turning the
effect
usingturning
less force
effect,
in doing
usingthese
less force
actions?
Levers can be used as:
•
Force-magnifier: decrease the force
needed for a purpose, like lifting a load
• Distance-magnifier: a small
movement near the pivot becomes a
lager movement at the other hand,
away from the pivot (hand of a clock)
W/S: 9L3 Force at
work
What is this? How does it work?
Activity
9.7
Scale
maker
9.8 The
principles of
moments
9.9 Calculating
moments
Learning objectives:
- State what is a moment
- List the factors that can change it, and
name its two possible directions
- Solve problems using the formula for
moments
- Perform a practical invetigation in
studying the principle of moments
What is happening in this situations?
How do they differ?
What is a moment?
Turning effect of a force
What are the factors that can change
a moment?
Force and distance
What is the formula to
calculate a moment
Moment = F x d
What is the SI unit of moment?
Nm
Problem: A 25 kg boy is on a
seesaw, 250 cm away form the
pivot. What is its moment?
F = 25Kg x 10 N/Kg = 250 N
Moment = 250N x 2.5m =
625 Nm
Moments in balance:
Seesaw example: What is
the direction of the F of
these two people?
Pointing downwards
What it the direction of the
turning forces?
Clockwise and anti-clockwise
Question: In a seesaw, if a heavier kid has a
mass that is double of the mass of a smaller kid,
what is the distance from the pivot that he
should be sited, to balance the seesaw compare
with that one of the smaller person?
Half
W/S: 9Lc/1
Investigating levers 1
W/S: 9L3 Levers
Practical: Activity 9.8
Balancing a beam
W/S: 9L4 Testing the
principle of moments
W/S: 9L4 Moments