24.When does static friction come into play? 25.Can we reduce friction to zero? 26.Why is it easier for the fish to swim in water? 27.What is a spring balance? 28.How does the friction depend on the nature of the surface? 29.What are the two factors on which the force of friction depends? 30.When the two surfaces are pressed harder, friction increases. Explain why? 31.Why is it easier to move the box already in motion than to get it started? or The sliding friction is slightly smaller than the static friction. Explain why? 32.Why are the soles of shoes and tyres of vehicles grooved? 33.We use ball bearings between the hub and axle of ceiling fan and bicycles. Why? 34.Why are lubricants applied between the moving part of a machine?
Answers
When the body is in rest or have tendency to move then it has static friction and when the body is in motion, the kinetic friction may oppose or may support the motion depending on the conditions. The direction of frictional forces is opposite of the Applied force on the object
What is Static Friction?
Static friction is a force that keeps an object at rest. Static friction definition can be written as:
The friction experienced when individuals try to move a stationary object on a surface, without actually triggering any relative motion between the body and the surface which it is on.
It can be explained as the force of friction which precisely balances the applied force for the duration of the stationary state of the body.
The static frictional force is a self-regulating force, i.e. static friction will at all times be equivalent and opposite to the force applied.Static FrictionR is the reaction force because of the weight W. the external force is F and fr is the friction. F = -fr when no motion takes place.
Static Friction Examples
Some real-life examples of static friction are given in the points below.
Papers on a tabletop
A towel hanging on a rack
A bookmark in a book
A car parked on a hill
You may also want to check out these topics given below!
Laws Of Friction
Friction And Its Application
Types Of Friction
Frictional Force
Laws of Static Friction
The maximum force of static friction is not dependent on the area of contact.
The maximum force of static friction is comparative to the normal force i.e., if the normal force increases, the maximum external force that the object can endure without moving, also increases.
Limiting Friction:
It is the highest value of static friction which comes into play when an object is just about to slide over the surface of a different object. For an exerted external force greater than the limiting friction, the body begins to move.
Once the motion has started, static friction cannot be considered. A new type of friction termed as kinetic friction comes into play.
Laws of Limiting Friction:
The direction of limiting frictional force is always contrary to the direction of motion.
Limiting friction acts tangentially to the two surfaces interacting.
The magnitude of limiting friction is proportional to the normal reaction amidst the two surfaces.
The limiting friction hinges upon the material, the nature of the surfaces interacting, and their evenness.
So long as the normal reaction is the same, the magnitude of limiting friction is free of the shape or the area of the surfaces in contact, for any two given surfaces.