Қысым тақырыбына арналған 7-сынып сабақ жоспары

8TH CLASSES PHYSICS DAILY PLAN

SUBJECT: PRESSURE GOALS: DURATION: IN PRACTICE:

PRESENTATION: Pressure: The perpendicular force acting on unit area is called as ‘pressure’.

 Examples and applications based on concept of pressure in daily life. (e.g.: slicing a bread, skiing, skating, snow-shoes, standing and lying on the beach...)

Force(F)

Weight(W)

 Formula: Pressure= Force/Area, in symbols: P= F/A

 Unit: Unit of force is in Newtons (N) and unit of area is in meter squared (m2). So unit of pressure is in N/m2. Briefly, it is called as ‘Pascal’ that is abreviated as ‘Pa’. There are some other unit expressions for pressure but they will be mentioned in proceeding lessons. Exercise: Find the pressure exerted on a certain area of 5m2 by a force of 20N.

Transmission of Force in Solids:  Structure of solids, liquids, and gases could be mentioned briefly.  Force is directly transmitted by solids.

F F

Pressure in Solids:  Solids exert a pressure on the area where they lie due to their weight. Example 1: The weight of the rectangular prism shown in the figure is given as 480N. The dimensions of the prism are 6m, 4m, and 2m. Find the pressure on three different surfaces of the prism.

h= 4m

w= 2m

l= 6m

Example 2: A carpenter is applying a force of 30N on the head of a nail with a hammer. The areas of the head and tip of the nail are given as 0,2cm2 and 0,001cm2 respectively. Express the ratio of pressure values exerted on head and tip of the nail.

Pressure in Liquids:  Liquids also exert pressure due to their weight and

gravity.

h= depth

 Derivation of the pressure expression for liquids from the definition of pressure: P= F/A; where F= mg: weight of the liquid P= mg/A; where mass= (volume)x (density)= (base area)x(height)x(density)  Therefore, P= Ahdg/A= hdg; where g expresses the gravitational pull of the earth.  Finally, the general pressure expression for the liquids due to gravity can be written as: Pressure exerted by a liquid on a certain point is equal to the product of depth of that point, density of the liquid, and gravitational attraction constant of the earth.  Liquids can flow because of the structure and orientation of their atoms or molecules. Transmission of Pressure by Liquids:  As a result of the former property, liquids transmit pressure in every direction without any change. This is an extremely applicable property of liquids.

 Pressure of a liquid in a certain container depends only on the depth of the point on which the pressure acts. (An example could be solved that shows pressure does not depend on the shape of the container.)

Communicating Vessels:

 A liquid always find its own level in a container since it is a fluid.  The levels of the liquid would be same if two or more containers combined at the bottom regardless of shape and volume.  This property could be used in water and gasoline tanks.

Hydraulic Lifts(Pascal’s Principle):

 They are constructed by using the incompressibility of the liquids. Since the liquids are incompressible they transmit the pressure due to their weight or a certain force in all directions without any change.  They are used for lifting heavy loads by a little effort. Load Force

Piston 1 Piston 2

Are

a

Liquid,d

A

P

A