Page 78 - Physics

Physics for Secondary Schools

sides of an object immersed in a static reaction force and it acts perpendicular (at
fl uid as shown in Figure 3.17. This is the right angle) to the surface in contact. For
reason why an object feels lighter when example, if a book is resting on a table,
immersed in a fl uid but heavier just above then the table is exerting an upward force
the surface of the fl uid. on the book in order to support the weight
Buoyant force of the book, as shown in Figure 3.18.

Normal force

Water
Cork

Weight Weight

Figure 3.17: Buoyant force
Figure 3.18: A normal force
Normal force
This is a support force exerted upon an When a person leans against a wall, the wall
object which is in contact with another supports the person by pushing him or her
stable object. The normal force is also called away perpendicular to the wall.

Torsional force
This is the force produced on a solid object when it is twisted. It is an elastic force
since the object returns to its original shape when the force is removed. An example of
torsional force is observed in twisting a rubber or a ruler, as illustrated in Figures 3.19.

(a) Normal (b) Twisted (c) Twisting a ruler between the ends

Figure 3.19: Illustration of torsional force

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Student’s Book Form One

Physics Form 1 Final.indd 72 16/10/2024 20:56