Thrust is the force applied perpendicular to a surface. Pressure is the effect of thrust per unit area and is calculated as thrust divided by area. Pressure depends on both the force and the area it acts upon - greater force or smaller area results in higher pressure. Examples are given where distributing force over a larger area reduces pressure, such as wide straps on school bags, broad tractor tires, and foundations of buildings.

1. Thrust and Pressure

2. Thrust
• The force applied on a surface in a
direction perpendicular to the surface.
SI Unit = Newton (N)

3. Pressure
The effect of thrust per unit area is called
pressure.
• Pressure is a scalar quantity.
• Pressure = thrust/area
• SI Unit – Pascal (Pa) 1 Pa = 1 N / 1m2

4. Pressure depends on two factors
1.force(thrust)-more force
more pressure
2.area -more area less
pressure
The same force produces less
pressure if it acts on a large
area but can produce large
pressure if acts on a small
area.”

5. Every day observation
School bags have wide straps so the weight of
bag may fall over a large area of the shoulder of
the student producing less pressure on shoulder.

6. • Sharp knife cuts
better than a blunt
knife so the force of
our hand falls over a
very small area of
object produces large
pressure.

7. The tractor have broad tyres so there is
less pressure on ground and do not sinking
to comparatively soft field.

8. It is easier to walk on soft sand if we have
flat shoes rather than shoes with sharp
heels.

9. The foundations of buildings and dams are
laid on a larger area to produce less
pressure

10. A wide belt is provided over the wheels of
an army tank.
The wooden or concrete sleepers are kept
below the railway line.

11. Now answer
• Define thrust. What is its unit?
• What is the relation between pressure, force and area?
• Why does a sharp knife cut objects more effectively than
a blunt knife?
• Why the tip of sewing needle is sharp?
• Why snow shoes stop you from sinking into snow?
• A cubical block of edge 2cm and of mass 5kg is kept on a
table top. Calculate (a) the thrust of the block on a table
top.
(b) the pressure of the block on the table top
Ans- 49N, 122500Nm-2