CBSE Book Class 8 Science Activity The Ball Bearing

FRICTION

Vidya lied down on bed to sleep. But sleep was nowhere near her. She kept staring at the ceiling fan. She  wondered, “Doesn't the fan ever wear out?” Well! It never has in the last five years, since Appa fixed it on  the ceiling. She went in search of her father with all these thoughts in her mind.  “Appa, I was wondering how is it that the ceiling fan has been rotating tirelessly without any wear and  tear all these years”, asked Vidya. Mr. Iyer, Vidya's father was very proud of his daughter and her never  ending questions.  He showed Vidya the inside of an old fan. He pointed out small spherical balls in the fan and told Vidya  that these are called ball bearings. 

“It  is  these  ball  bearings  that  reduce  friction  in  many  machines  and  prevent  then  from  wearing  out  quickly”, said appa. Vidya looked confused. “I don't understand how they work”, said Vidya. “Come, let me show you”, said Appa. Why don't you also make the model with Vidya's father? You will need: 

Glass marbles, three bottle caps (like those on jam jars) of different sizes, a book.

Please refer to the link below - CBSE Class 8 Science Activity The Ball Bearing