Page 73 - Physics

Introduction to force

Frictional force Acti vity 3.4
This is the force which opposes motion
between two surfaces of objects in Aim: To demonstrate
contact. Friction occurs when one surface frictional force.
of an object is resting or moving over Material: Wood blocks
another. Friction is a very common force.
Whenever one object slides over another Procedure
object, friction tries to stop the movement. 1. Rub the palms of your hands against
For example, if a block is made to rest on a each other. What do you feel?
table, its weight acts on the table. But if 2. Make tiny rails on the surfaces of
the block is tied with a string and made the two wooden blocks.
to slide (pulled) as shown in Figure 3.8,
there is some kind of resistance to the 3. Vigorously, rub the two blocks of
movement of the block. This is the work wood against each other. What do
of friction. you observe?

Block Questions
(a) Explain your observations.
(b) What is your conclusion?

Sliding
String When two objects in contact rub against
each other, heat is produced. Frictional
force, unlike other forces, produces heat.
Figure 3.8: Sliding a block on the table top
Frictional force results to wastage of energy
Frictional force occurs depending on the in the form of heat. In engines, friction can
nature of the surfaces of bodies in contact.
Friction produces heat, as is the case in wear the moving parts resulting in poor
matchsticks. Wear and tear of car tyres performance of the engine.
and shoe soles are caused by friction. For
example, Figure 3.9 (a) shows new tyres Acti vity 3.5
and (b) shows worn tyres due to frictional
force. Aims: To demonstrate the
magnitude of friction
Materials required:

brick, hook and
spring balance

Procedure
1. Tie a string around a brick and attach
(a) New tyres (b) Worn out tyres a hook to it.

Figure 3.9: New and worn car tyres 2. Attach the spring balance to the hook
showing the effects of friction as shown in Figure 3.10.

67

Physics Form 1 Final.indd 67 16/10/2024 20:56