Page 145 - Physics

Pressure

20 N another, the greater the pressure it exerts.
P =
−6
1×10 m 2 Thus, the pressure between two solid
surfaces depends on the force between
= 2.0 ×10 N/m 2 the surface and the area of contact of the
7
Therefore, the pressure exerted at the tip two surfaces.
of the needle is 2.0 ×10 N/m .
7
2
Applications of pressure due to solids
Pressure due to solids has wide practical
Dependence of pressure on surface applications. The effect of pressure is
of contact applicable when using nails, screws,
From examples 7.1 and 7.2, it is noticed that pins, spears and arrowheads. These items
the greater the surface of contact, the lower are given sharp points to increase their
the pressure exerted. Also, the smaller the penetration abilities. Figure 7.4 shows
surface of contact of an object, the greater examples of solid objects with sharp
the pressure it exerts. Generally, to create points.
a large amount of pressure, you can either
exert a large force or exert a force over a
small area or do both.

Acti vity 7.2
Screw Nail Pins
Aim: To demonstrate the
dependence of pressure on Figure 7.4: Objects with sharp points
the surface of contact.
Materials: Wires of varying diameters, Knives blades and razor blades have sharp
and bars of soap cutting edges, as shown in Figure 7.5. Sharp
Procedure edges have a minimal area over which
1. Use a thin piece of wire to cut a bar an applied force exerts pressure, which
of soap into half. facilitates cutting.
2. Use a thick piece of wire to cut a
similar bar of soap into two pieces.
3. Record your observations. Knife

Questions
(a) What is the difference between Razor blade
cutting a bar of soap using a thin Figure 7.5: Objects with sharp edges
wire and when using a thick wire?
(b) Explain your observation. Some living organisms make use of
pressure for self-defence. For example, a
It is easier to cut a bar of soap using a thin fi sh uses its sharp fi ns to protect itself. The
piece of wire than a thick one. This shows fi ns infl ict pain on an intruder’s body. The
that the smaller the surface in contact with fi sh fi ns are shown in Figure 7.6.

139

Physics Form 1 Final.indd 139 16/10/2024 20:57