Page 77 - Physics

Introduction to force

so that the other layers have to slide over Oil takes longer time to fl ow into the beaker
each other. Friction between the layers stops than water. On the other hand, it takes
them from sliding easily, thereby making longer for honey to fl ow into the beaker
the whole liquid fl ow slowly. Another effect than it does for cooking oil. Honey has a
of viscosity is that a highly viscous liquid higher resistance to fl ow. Therefore, we
will resist the motion of objects through it. can say that cooking oil is more viscous
High viscosity is a necessary property in than water and honey is more viscous than
lubrication. Lubricants like oil and grease cooking oil.
are meant to reduce friction in the moving
parts of machinery. Grease has a higher Tensional force
viscosity than oil. Tension is the force exerted on an object by
a stretched material. It is the force that is
Acti vity 3.6
transmitted through a string, rope, cable, or
Aim: To demonstrate viscosity of wire when it is pulled tight by forces acting
substances. from opposite ends. The tension force is
Materials: Water, cooking oil, directed along the length of the wire and
honey or lubricating oil, pulls outwards along the two ends of the
beakers, stopwatch, plastic rope. Figure 3.16 shows the tension force
can and seal tape along the stretched cable wire.
Procedure
1. Clean a plastic can and drill a hole
near the bottom.
2. Seal the hole using seal tape. Tension
3. Fill in the can with water.

4. While starting the stopwatch, unseal
the hole on the can.
5. Allow all the water to fl ow out from Weight
the can into the beaker. Record the
time taken.
6. Clean the can, dry and reseal the
hole. Figure 3.16: Tension force along the cable wire
7. Repeat steps 3 to 6, using oil and Buoyant force
honey one at a time.
Buoyant force is the force that causes
Questions objects to fl oat. It is the force exerted on
(a) Compare the rate of fl ow of the an object that is partly or totally immersed
liquids. in a fl uid. Buoyant force is caused by
(b) Account for the differences observed. differences in pressure acting on opposite

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Physics Form 1 Final.indd 71 16/10/2024 20:56