FRICTION i) Force acting on a body can be measured by a . ii) Friction is caused by the on the two surfaces in contact iii) Frictional force exerted by fluids is also called iv) The frictional force on an object in a fluid depends on its , and. v) can be used to reduce friction vi) is also produced with friction. vii) Shape of the objects moving in the fluid is to overcome friction exerted by liquids. viii) are used in the machines to protect their surfaces from wear due to friction. ix) Soapy floor is slippery due to friction. x) Ball bearing are used to convert static friction into friction. Q2 Why is it difficult to walk on a smooth and wet floor? Q3 Why front portion of an aeroplane has a spherical shape or is streamlined? Q4 On what principle do ball bearings work? Q5 Give construction and working of a spring balance. Draw the diagram also. Q6 “Force of friction is much greater on a rough surface.” Explain. Q7 Give some advantages of friction. Q8 Writ e two advantages of rolling friction. Q9 Mention two ways to reduce friction? Q10 differentiate between static and sliding friction. Q 11 a) Two objects, A and B, one over the other, are moving with the same velocity. Which of the following statements is correct? A) Friction on A is in the forward direction. B) Friction on A is in the backward direction. C) Friction on B is in the forward direction. D) No friction acts between A and B. b) When we rub our palms together vigorously, they become warm because muscular energy is converted into heat energy due to the friction between the palms. A) True B) False Q12. What kind of tyres are used in the racing cars and why?
Answers
Answer:
1.FORCE CHANGES DIRECTION OF MOTION - EXAMPLE
When a ball hits against a wall, it bounces back in the opposite direction. So the force exerted by the wall on the ball changes its direction of motion.
FORCE CHANGES SHAPE OF OBJECT - EXAMPLE
When a hammer strikes a hot rod, the rod bends. The force exerted by the hammer on the rod changes the shape of the rod.
EXAMPLES FOR EFFECT OF FORCE - EXAMPLE
Force may bring the following change:
1) Can change the state of an object(rest to motion/ motion to rest):For example, pushing a heavy stone in order to move it.
2) May change the speed of an object if it is already moving.For example,catching a ball hit by a batsman.
3) May change the direction of motion of an object.For example,footballer kicks a moving ball to change its direction.
4) May bring about a change in the shape of an object.For example, blowing air in balloon.
5) May cause some or all of these effects.
2. Contact forces Non-contact forces
These are forces which need a physical touch on the object to act upon it. These are forces which do not need a physical contact to act on an object.
These may or may not be natural forces. These are natural forces
They can not work from a distance. They can work from a distance as well.
Its various types are applied force, normal force, tension frictional force its various types are magnetic force electrostatic force,gravitational force
Examples player kiicking a ball game of tug of war rolling ball stops itself horse pulling a cart etc, Examples: magnet attracting iron nails, mango falling from tree, charged plastic ruler attracts bits of dry - paper etc.
3.All objects have a tendency to fall towards the earth when thrown up due to the influence of gravity. The gravitational force acts upon the body and it tends to fall towards the earth. The force of attraction between two bodies that has mass.
4.The mass of an object is a measure of the object's inertial property, or the amount of matter it contains. The weight of an object is a measure of the force exerted on the object by gravity, or the force needed to support it. The pull of gravity on the earth gives an object a downward acceleration of about 9.8 m/s2.
5.Friction depends on the nature of surfaces in contact. For a given pair of surfaces, friction depends upon the state of smoothness of those surfaces. The force of friction is greater if a rough surface is involved. Friction is caused by the irregularities on the two surfaces in contact.
6. The main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy. ... Due to friction, engines of automobiles consume more fuel which is a money loss.
7. The use of bearing surfaces which are sacrificial by themselves, such as low shaving materials, is an example. There are many ways to minimize friction. Replace the rolling element rolling tension with rolling element rolling element rolling bearing.Friction can be significantly reduced if either the object or the surface is smooth and straight or the opposite sometimes, tires in cars are specially made to fight friction when needed and reduce it (some cars increase friction but that's a whole different thing), also when planes are speeding up on the lane they need to minimize friction to an extent they will be going extremely fast, fast enough to take off so engineers and workers always make sure to make lanes organized and smooth without even a small rock on them and the wheels of the plane rather smooth to decrease friction the best they can. Sometimes friction goes against the object and doesn't let it move smoothly (you get a ring stuck on your finger, the door knob is moving more rustly, doors and such things are creaking more), then that requires some oily and and with a consistency to make the surface smooth and reduce the friction for smoother movement.
You can check the work by this too
Explanation: