FORM 1-PHYSICS-PRESSURE

PRESSURE
Dependence of Pressure on Surface of Contact
Explain dependence of pressure on surface of contact
The pressure in solid depends on the surface area of contact. A force (F) applied onto a small area exerts a higher pressure as compared to when it is applied onto a large surface.
Pressure in solid = Force applied/Area of contact.
Example 1
A block of wood that weighs 30N and measures 5m by 10m by 4m. If it was placed on a table with the largest possible area (5mx10m) in contact with table, exerts less pressure than it would when placed with its smallest possible area (5mx4m) in contact with table.
Solution
Data:
Force = 30N
Largest base area = ?
AL = 10mx5m = 50m2
P = F/A = 30N = 0.6N/30m2
Pressure = 0.6N/m2
Force (F) = 30N.
Small base are = ?
As = 5mx4m
As = 20m2
P= F/A = 30N/20M2 = 1.5 N/M2
Pressure = 1.5 N/M2
Example 2
A tip of needle has a cross- sectional area of 1x106m2. If doctor applies a force of 2N to a syringe that is connected to the needle, what is pressure is exerted at the tip of the needle?
Soln:
Data:
Area (A) = 1x106m2
Force (F) = 20N
Pressure =?
P = F/A
P = 20 = 2.0x107 N/M2
The pressure extended by the needle lip is 2.0x107N/m2
Example 3
A rectangle metal block with sides 105m by 1.0m by 1.2m rests on a horizontal surface. If the density of the metal is 7000kg/m3. Calculate the maximum and minimum pressure that the block can exerts on the surface.
(Take the weight of 1kg mass to be 10N)
Solution:
Data:
Dimension = 1.2m,1.5m,1.0m.
Density = 7000kg/m3
Maximum pressure (Pmx) = ?
Minimum pressure (Pmn) = ?
Volume = 1.2x1.5x1=18m3
Density = mass/ Volume
7000kg/m3 = mass/18
Mass = 7000x18 = 126000Kg
1kg = 10N
126000Kg = ?
F = 1260000 = 1.26 x 106
Force of metal = 1.26 x 106
A1 = 1.2 x 1.5= 18m2
A2= 1.2m2= 1.2mx1m=1.2m2
A3= 1.5 x 1m= 1.5m2
Amx = 18m2
Amin = 102m2
Pmn = F/Amx =1.26 x 106N/18M2 = 1.26X106/1.8 X101
Maximum pressure = 1.05x106N/m2/maximum pressure= 0.7x105N/m2
The Applications of Pressure due to Solids
Identify the applications of pressure due to solids
It is used to make different objects like screw, nails, pins, spears and arrows. This item is given sharp points to increase their penetrating power.
It helps some of living organisms for self-defence. A fish uses its sharp fins to protect itself.
When one walks on shoes with sharp pointed heels they exert greater pressure on the ground than when wearing flat shoes.
It helps in construction of railways. During the constructions of railways, wide wooden or concrete sleepers are placed below the railways tracks. This provides a larger surface area over which the weight of the train acts. This is a safety measure to train tracks.
Buildings are constructed with wide foundations to ensure that the weight of the building acts over the layer area.
Tags:

Powered by Blogger.