Page 137 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

When a body moves or tends to move on the surface of another
body, a force is experienced parallel to the surface which opposes
the relative motion between them. This is friction.

Is the same opposing force experienced during all contact
movements between bodies? Let's examine.
Different Types of Friction

Take a look at the pictures in which two children are trying to
move a log.

Fig. 10.6 (a) Fig. 10.6 (b)
Which of these methods is easy in moving objects - by dragging
or by rolling?

Let's do an experiment.
Place a wooden block on a polished table as shown in the
figure. Tie a string at one end of the wooden block and
hang a pan on the other end. Allow the string to pass
through a pulley. Place identical iron nails in the pan one
by one. Observe the number of nails placed when the
wooden piece begins to move.
Now repeat the experiment placing two cylindrical
pencils between the wooden piece and the table,
Fig. 10.7
perpendicular to the direction of motion.
On placing how many nails in the pan did the wooden
piece begin to move?
In which of the two situations is the force applied to move
the wooden piece lesser?
See 'gharshanam When was it necessary to apply more force, while sliding
undakunnathengane'
in School Resources in the wooden piece or while rolling it over the pencils?
IT @ School If so, in which situation is the opposing force less?
Edubuntu.

136 Basic Science VIII