The total perpendicular force exerted by a body on the surface in contact is called thrust. Pressure is defined as the thrust per unit area of a surface. The SI unit of pressure is Pascal (Pa) which is Newton per square metre( N/m^{2}). If ‘P’ is the pressure exerted by a body of area ‘A’ when force ‘F’ is applied then,
P = \(\frac{F}{A}\)
Pressure plays a significant role in our day to day activities. Sometimes we should increase pressure and sometimes we should decrease it. A drawing pin is broad at the thumb side but sharp and pointed at another end. It is done to reduce pressure at the thumb and to increase pressure on the drawing board. The force of our hand falls over a large area of the drawing pin and produces high pressure on the pointed edge of the pin. The effect of same force on different areas are different.
If ‘F’ be the force and ‘A’ be the area of the body then pressure exerted by the body is given by,
Pressure (P) = \(\frac{Force (F)}{Area (A)}\)
Or, P = \(\frac{F}{A}\)
From the above equation, we can conclude that,
Less pressure is exerted when a force acts over a large area of a surface and more pressure is exerted when the force acts on a small area of a surface. Same force can produce different pressure depending upon on the area over which it acts.
Example
A large brick of 10N occupies 1m^{2} surface area. Calculate the pressure exerted.
Solutions:
We have,
Force (F) = 10N
Area (A) = 1m^{2}
Pressure = ?
According to the formula,
Pressure (P) = \(\frac{Force (F)}{Area (A)}\)
Or, P = \(\frac{F}{A}\)
Or, P = \(\frac{10}{1}\)
Or, P = 10 Pa.
\(\therefore\) The pressure exerted by the brick is 10 Pa.
Activity
Bring a knife and a potato or any other vegetable. Then cut the potato with both sides of the knife i.e. by the blunt edge and sharp or pointed edge. What difference do you observe while cutting potato by both sides of the knife? What do you conclude from this activity?
Force acting per unit area is called pressure. The factors in which pressure depends are as follows,
The differences between force and pressure are as follows,
Force |
Pressure |
It is a pull or pushes acting on a body. |
It is the thrust acting per unit area. |
Its SI unit is Newton (N). |
Its SI unit is Pascal (P). |
It is the cause of pressure. |
It is the effect of force. |
It is easier to cut with a sharp knife than a blunt one because effect of force will be more on small area than large area. So, pressure due to sharp knife is more and blunt knife is less.
Wooden sleepers are kept below railway line so that there is less pressure of the train on the ground and railway line does not sink into the ground.
Camels can walk easily on sand in desert as compared to horses or donkeys because they have broad and flat soles which exert less pressure on the sand.
A square box of 500N occupies 5m^{2} surface area. Calculate the pressure exerted by the square box.
Solutions:
We have,
Force (F) = 500N
Area (A) = 5m^{2}
Pressure (P) = ?
According to the formula,
Pressure (P) = \(\frac{Force (F)}{Area (A)}\)
Or, P = \(\frac{F}{A}\)
Or, p = \(\frac{500}{5}\)
Or, P = 100 Pascal
\(\therefore\) The pressure occupied by the square box is 100 Pa.
Solution:
We have,
Force (F) = 200N
Area (A) = 2m^{2}
Pressure (P) = ?
According to the formula,
Pressure (P) = \(\frac{Force (F)}{Area (A)}\)
Or, P = \(\frac{F}{A}\)
Or, p = \(\frac{200}{2}\)
Or, P = 100 Pascal
\(\therefore\) The pressure occupied by the brick is 100 Pa.
Solutions:
We have,
Force (F) = ?
Area (A) = 10m^{2}
Pressure (P) = 50pa.
According to the formula,
Pressure (P) = \(\frac{Force (F)}{Area (A)}\)
Or, P = \(\frac{F}{A}\)
Or, 50 = \(\frac{F}{10}\)
Or, F = 50 \(\times\) 10
Or, F = 500N
\(\therefore\) The force of the body is 500N.
Solutions:
We have,
Force (F) = 180N
Area (A) = ?
Pressure (P) = 60pa.
According to the formula,
Pressure (P) = \(\frac{Force (F)}{Area (A)}\)
Or, P = \(\frac{F}{A}\)
Or, 180 = \(\frac{60}{A}\)
Or, A = \(\frac{60}{180}\)
Or, A = 0.33m^{2}
\(\therefore\) The area of the brick is 0.33m^{2}
Solutions:
We have,
Force (F) = 81N
Area = l^{2} = 3^{2} = 9m^{2}
Pressure (P) = ?
According to the formula,
Pressure (P) = \(\frac{Force (F)}{Area (A)}\)
Or, P = \(\frac{F}{A}\)
Or, p = \(\frac{81}{9}\)
Or, P = 9 Pascal
\(\therefore\) The pressure of the square box is 9 pascal.
The cutting edge of knives are sharpened to
ASK ANY QUESTION ON Pressure
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