Page 76 - Physics

Physics for Secondary Schools
submarine, in Figure 3.14 must overcome air resistance above the water surface and
water resistance beneath it.
(a) A cyclist
Figure 3.13: Effect of air resistance
Figure 3.14: Submarine beneath and above
water surface
Task 3.2
Discuss why engineers spend much
time trying to reduce fl uid resistance in
cars, ships, and planes.
Viscous force
Viscous force is the resistance force
provided by a fl uid when it is subjected
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Physics Form 1 Final.indd 70
(b) A parachutist
to a tangential force. The force acts to
oppose the fl ow of the fl uid past the
object. From day-to-day observations,
water has a smaller viscous force than
cooking oil. On the other hand, honey has
a larger viscous force than cooking oil.
The measure of resistance of the fl uid to
its fl ow past a surface is referred as the
viscosity of the fl uid. Thus, honey has a
higher viscosity than water. Figure 3.15
shows how one can visually compare the
viscosity of different fl uids.
(a) Water fl ow (b) Honey fl ow
Figure 3.15: Comparison of water and
honey viscosity
When a highly viscous liquid runs off a
surface, its inner layer sticks to the surface
Student’s Book Form One
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