Hello Students, Toady we are starting our Class 8 Science Chapter-5 friction of DAV Book 2021. If You are in class 8 and looking for Class 8 Science Chapter- Chapter-5 friction CBSE/DAV Book Solution 2021. Then you are absolutely at the right place of knowledge decode
Class 8 Science Chapter 1 : The Cell- Its Structure and Functions
class 8 science chapter 2 : Microorganisms : friends or foes
class 8 science chapter 3 : Metals and Non-metals
class 8 science chapter 4 : force and pressure
This Post Contains All The Exercises of Chapter 5 Science Of Class 8 .
A.Fill In The Blanks.
B.Math The Following.
C.Tick(√) The Correct Option
D.Answer The Following Questions in Brief
E.Answer The Following Questions
A. FILL IN THE BLANKS.
- friction always opposes any relative motion between the two surfaces that are in contact with each other.
- static friction is always greater than sliding friction.
- sportsmen use shoes , fitted with spikes , to increase friction between their shoes and the ground.
- sprinkling of talcum powder , on the carrom board , helps to reduce friction.
- frictional force , on an oject moving in a fluid , depend on its shape and speed.
- the shape of an aeroplane is streamlined to reduce , the effects of friction , due to air.
B. STATE TRUE OR FALSE FOR THE FOLLOWING STATEMENTS.
- When a body slids over smooth and wet surfaces, the amount of interlocking of irregularities, of the two surfaces in contact , increases. false
- If a car moves eastwards , the force of friction acts southwards. false
- Friction depende on how hard the two surfaces press against each other. true
- the sole of shoes and the tyres of the vehicles are treaded to decrease the effects of friction. false
- Lubricants can be liquids, semi-solids or solids. true
- friction can be increased by using ball bearings between the moving parts of machines. false
- fluid friction can be minimised by giving suitable shapes to the objects moving through the fluid. true
C. TICK THE CORRET OPTION.
- Suppose your writing desk is tilted to a position where a book kept on it just starts sliding down. the figure, showing the correct direction of frictional force acting on it, is- (d)
- two boys are applying oppositevly, direced , and equal in magnitude , force on a box . in such a case , the force of friction , that would exist between the lower end of the box and the ground , would be called- (b)static friction
- The energy,’used up’ in overcoming friction gets converted mainly into- (b)heat energy
- Rahul rolls a ball on a wooden surface . The ball covers a certain distance before coming to rest . To make the same ball cover a longer distance, before coming to rest , rahul should- (c)sprinkle talcum powder on the wooden surface.
- A block is sliding on a horizontal surface .the force of friction between the two can be increased by- (d)by putting a second identical block on top of the given block
D. ANSWER THE FOLLOWING QUESTIONS IN BRIEF.
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