Lesson Plan of Units of Pressure & its Application (Force & pressure)General Science Grade VIII
Lesson Plan of Units of Pressure & its Application (Force & pressure)
General Science Grade VIII
Students’ Learning Outcomes
·
Define the term pressure.
·
Identify the units of
pressure.
·
Explain hydraulics and
hydraulic system by giving examples.
Information for Teachers
·
A force is push or pull.
·
Force can be classified into
contact or non-contact forces.
·
Other examples of forces:
1.
Squeezing.
2.
Twisting.
3.
Stretching.
4.
Folding.
·
When a force acts on an
object it exerts pressure. The pressure acts at a right-angle to the object
itself, and its strength depends on the amount of force and the area over which
it is applied.
·
When we apply a force on a
body then according to conditions it has two effects like:-
o When force applied on small area, it gives high
pressure e.g. force applied on the sharp edge of a knife produces a high
pressure due to which cut things easily.
o When force on a large area is applied it gives
low pressure, e.g. camels have wide feet to spread their weight on the sand
which lowers the pressure and allows them to walk on sand without sinking in
sand.
o Pressure is the force exerted on a unit area.
Mathematically, it is represented as P=F/A, where F=force, A=area and
P=pressure.
o Pressure is measured in Pascal’s (Pa). This is
the S l unit of pressure. It is a pressure of one newton per meter square
o Kilopascal (k P a) is 1000 pa.
o Pressure is everywhere. It operates many
machines and affects our weather. Solids liquids and gases all apply pressure
to the surfaces they touch.
o Pneumatic machines are driven by the pressure
of gases, usually air. Unlike liquid, air can be compressed into a smaller
space and this increases its pressure.
o “Hydraulics” is the study in which we deal with
mechanical properties of liquids.
o Hydraulic system is used in car braking system.
A small piston connected with one end of a tube is pressed with a small force
by pressing on the brake pedal; consequently the large piston connected to the
other end of the tube is pushed out with a much larger force which pushes the
brake brushes. This results in stopping the car ultimately.
Concept Map
Material / Resources
Balloon, water, common pin, tread, 2 syringes,
water, rubber tube 2*10cm, 2 cylinders, 1 big and 1 small, 2 cork pistons
according to the sizes of cylinder, toy car or any other thing
Worm up activity
·
Perform a following activity
involving the students for giving them the concept of gas pressure.
Activity 1
·
Fill the balloon with water.
·
Tie the upper end of balloon.
·
Water exerts pressure
downward so the balloons look like a drop.
·
Make several holes on the
balloon’s surface. The water will start dropping down.
·
When the balloon is squeezed
gently, the water starts to drop down from every hole equally and more speedily.
·
After the demonstration tell
the students that when we apply a small amount of force to squeeze the balloon,
it increases the pressure on water and ultimately water comes down from the
holes with more speed. Now announce that we will learn about pressure, its
units & its functions in the form of hydraulics.
Development
Tell the definition of
pressure to the students first as force acting per unit area is called
pressure. Tell the factors upon which pressure depends. Write the following formula & units as:-
P= F/A (N/m2
Activity 1
·
Ask the students a day before
to bring clay and a coin. Divided the students into 5 or 6 groups. Ask the
students to press the coin flat and then edgewise. Now ask the following
questions from the students.
Activity 2
·
Clear the student’s concept
by performing the following activity under his/her assistance.
·
Divide the students in pairs
·
·
Instruct o fill the syringes
about half with water.
·
Put the hollow rubber tube
from both sides at nozzles of the syringes as shown in the figure.
·
Ask the students to push the
plunger of one syringe inward, the pressure exerted through it will push the
plunger of other syringe outward direction.
·
Now as a student to push both
the plungers inward with the same force. There will be no movement in the
plungers because the amount of pressure on both sides is equal.
Activity 3
·
Perform the following
activity to give the concept of hydraulics.
·
Instruct the students to attach
the cylinder according to the figure shown above.
·
Instruct the students to
place a toy car on the piston of larger cylinder.
·
Add some weight of 50 gm. or
more on the piston of smaller cylinder. The student will observe the changes.
Now add more weight on the piston.
·
As well as the weight
increases on the small piston, the amount of pressure exerted by it will
increase on the larger piston, so the car will rise up.
·
Now tell the students that
hydraulics lift at service stations work in the same manner.
·
Ask the students to identify
more hydraulic systems which can used in
Sum up / Conclusion
·
The hydraulic system works
out on the principle of 2nd activity.
·
The pressure transmits
equally in all directions.
·
Amount of pressure increases
with the depth of the liquid.
·
Larger weights can be lifted
by applying smaller force using hydraulic systems.
Assessment
·
Ask the following questions:
Q1. At service station why hydraulic
lifts are used?
(Expected response: To lift the car
so that it can be washed properly)
Q2. Why people with high heel shoes are
not allowed on jogging tracks?
(Expected response: Because high
heels exert more pressure than flat shoes which make
The ground uneven)
Q3. When will the pressure be more, while
standing on the mattress or when lying on the
Mattress
(Expected response: Pressure will
be more when one stands on the mattress)
Follow up
·
Make a diagram of hydraulic
system from the books on their notebooks.
·
How pressure cooker works?
Describe its principle.
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