Students` Learning Outcomes
· Describe friction and its causes
· Explain the advantages and disadvantages of friction.
· Suggest methods to reduce friction.
· Identify what cyclist, swimmers and parachutists do to reduce friction.
Information for Teachers:
|The force which opposes the motion of one object over another is called friction.
· It is caused by the roughness of the two surfaces.
· Friction can be a help or a hindrance for motion. It prevents objects from starting to move.
· It can be reduced by making surfaces smooth e.g. by making surface wet or by oily.
· The friction of rolling objects is less than the sliding objects.
· To minimize air or water friction, the aeroplanes, cars, ships, boats etc. are shaped pointed or wedge like from the front.
· The cyclists, swimmers and parachutists wear tight to dresses and cover their heads with tight caps to reduce the friction.
Material / Resources:
A book, a ball , wooden block, glass sheet, oil, textbook.
· Ask a student to push a book lying on the table.
· Then ask the students what happened to book? (Student’s response: The book moved on the table. Eventually it slowed down and stopped. )
· Why do bodies stop? (Students’ response: There must be a force acting opposite to the motion of objects)
· What is that force which stops the movement of objects? (Students’ response: When an object moves, it rubs against the surface on which it moves . Rubbing provides an opposing force. This force is called friction.)
· Ask the students what does cyclist do to stop a bicycle? ( Students’s response: He applies brakes.)
· Why does brake stop a moving bicycle? (Students’ response: The brakes rubs against the rim of the wheel and hence opposes the motion of bicycle.)
· Draw out the conclusion that the force which opposes the motion of the objects is called friction.
· Place a wooden block on the table and tell a student to push it to slide over the surface of the table.
· Ask a student what opposes the motion of the wooden block on the table? (students’ response: The roughness of surfaces.)
· Then place glass sheet on the table and ask the same student to push the wooden block over the surface of the glass sheet.
· Ask the students what difference do they notice when the block moves over two different surfaces (students; response: The block comes to rest after covering greater distance on the glass sheet)?
· Inform them that the surface of table opposes the motion more than the glass sheet.
· Ask the students why is sliding of the wooden block over the glass sheet easier than over the table? (students’ response: The surface of the glass sheet is smooth whereas the surface of the table is rough).
· Inform them that the roughness of surfaces causes friction.
· Take a glass sheet.
· Ask the student to rub the palm of her/his hand on it.
· Now pour a little oil on the sheet.
· Ask the student to rub the hand again on oily sheet.
· Then ask what difference do you feel on rubbing the dry glass sheet and the oily sheet? (students’ response: The oily surface has less friction.)
· Ask them how can we decrease the friction? (students’ response: By applying oil or grease between the surfaces which slide over each other.)
· Take a trolley school bag with wheels attached to its bottom.
· Ask a student to drag the bag on a smooth floor over the side without wheels.
· Then ask him/her to drag it over the wheels.
· Ask the students, is it easier to move the bag or wheels? (students’ response: yes , the wheels reduce friction.)
· Inform the students that friction can also be reduced by using wheels attached to the heavy objects to make the movement easier.
Sum Up / Conclusion:
The teacher should ask the students: What have you learnt today and the write the conclusions on the board:
· The forces which opposes the motion of the objects over another is called friction.
· Friction is sometime desirable and some other times a hindrance.
· The roughness of surface causes friction.
· Friction can be reduced by making surfaces smooth, by oiling the surface or by using wheels.
· Make a table on the board and ask the students to copy on their note books.
· Ask them to make a list of objects from their surroundings, offering more friction and less friction.
· Involve the students in solving the questions given at the end of chapter/ unit in textbook.
· Ask the students to analyze how friction can be desirable and undesirable in our everyday lives . Use examples to support your statements.
· Ask them to hypothesize what your life would be like if there were no friction. Which actions would be more difficult? Which would be easier?
· Ask them, is the friction between a child and surface of a ‘slide’ more or less? How does this make the slide work? How could you reduce the friction between yourself and the slide to make you go faster?