3B1 Friction Flashcards
Differentiate between normal force and frictional force, and measure static and kinetic friction.
Define:
Normal force
Perpendicular force exerted by a surface on an object in contact with it.
This force balances the component of the object’s weight perpendicular to the surface.
Define:
Friction
Force that opposes the relative motion or tendency of motion between two surfaces in contact.
Frictional forces can be static (preventing motion) or kinetic (resisting motion already occurring).
True or False:
Frictional force always acts parallel to the surface of contact.
True
Frictional forces arise due to surface irregularities and interactions at a microscopic level.
Fill in the blanks:
The magnitude of friction depends on the ______ and the ______ of the surfaces in contact.
normal force; coefficient of friction
The coefficient of friction quantifies the frictional interaction between surfaces.
What causes friction?
It is caused by the interaction of microscopic bumps on the surface of objects.
Surface roughness and material properties determine the magnitude of friction.
Why is friction necessary in everyday life?
Friction allows us to walk, drive, and hold objects without slipping.
While beneficial in some contexts, friction also causes wear and energy loss in mechanical systems.
What is the formula for calculating the normal force of an object resting on a horizontal surface?
FN =mg
In the equation, m is mass and g is gravitational acceleration. On inclined planes, the normal force changes based on the angle of inclination.
How does the normal force change on an inclined plane?
The normal force is reduced to FN=mgcosθ, where θ is the angle of inclination.
The component mgcosθ acts perpendicular to the inclined surface.
True or False:
Friction can occur without a normal force.
False
The normal force is essential for generating frictional forces.
What is the effect of an inclined plane on frictional force?
Friction decreases because the normal force is reduced.
The component of weight parallel to the plane increases, aiding motion.
Define:
Angle of repose
The steepest angle of an inclined plane at which an object remains stationary due to friction.
The angle of repose is used in studying the stability of granular materials.
True or False:
The normal force is always equal to the weight of the object.
False
The normal force depends on the orientation of the surface and additional forces acting on the object.
What role does the normal force play in friction?
The normal force determines the maximum possible frictional force.
Frictional force is proportional to the normal force via the coefficient of friction.
What happens to friction if the normal force increases?
Friction increases proportionally to the normal force.
This relationship explains why heavier objects experience more friction.
Fill in the blank:
Frictional force is calculated as F=μ___.
N (normal force)
μ is the coefficient of friction, which varies between static and kinetic friction.
Why do ice and smooth surfaces have low friction?
They have small coefficients of friction due to minimal surface irregularities.
This property makes ice ideal for activities like skating but hazardous for walking.
Fill in the blank:
Friction is a force of _____ against two objects sliding against each other.
resistance
Friction opposes the relative motion or tendency of motion between two surfaces in contact.
Why does friction cause wear and tear in mechanical systems?
It generates heat and stresses between moving parts, leading to material degradation over time.
Regular maintenance and lubrication help reduce wear.
How does frictional force play a role in braking systems?
Friction between brake pads and the wheel slows down or stops a vehicle.
Brake systems are designed to maximize friction for effective stopping power.
How does friction affect the motion of a ball in sports?
Friction between the ball and the surface slows its motion, allowing for control in games like soccer or basketball.
Players often exploit friction to dribble, stop, or spin the ball effectively.
What is the difference between static and kinetic friction?
Static friction prevents motion, while kinetic friction opposes motion already occurring.
Static friction is generally greater than kinetic friction for the same surfaces. This means that it usually takes more force to start moving an object than to keep it moving.
What happens when the applied force exceeds the frictional force?
The object will move.
This applies to both static and kinetic friction scenarios.
What does the graph of applied force against frictional force illustrate?
The regions of static and kinetic friction.
The threshold of motion is the point where an object starts moving.
True or False:
Friction is independent of the contact area between surfaces.
True
Friction depends on the normal force and the coefficient of friction, not the contact area.
Define:
Coefficient of friction
Number that quantifies the ratio of the frictional force between two objects to the normal force pressing them together.
The coefficient of friction varies between materials and can be static or kinetic depending on whether the surfaces are stationary or in motion.
What are the typical ranges of coefficients of friction?
They range from 0 (no friction) to over 1 (high friction), depending on the materials and surface conditions.
For example, ice on steel has a low coefficient (around 0.05), while rubber on dry asphalt can exceed 1.
What is the coefficient of static friction?
It is the ratio of the maximum static frictional force to the normal force.
The coefficient of static friction determines the threshold to initiate motion.
Fill in the blank:
The coefficient of friction is a ______ quantity.
dimensionless
This is because both the frictional force and normal force are measured in Newtons.
What happens if the coefficient of friction is zero?
There would be no frictional force between the surfaces.
This is an idealized situation, as all real surfaces have some friction
Fill in the blank:
The coefficient of kinetic friction is ______ than the coefficient of static friction.
smaller
Kinetic friction is lower because surfaces are already in motion.
How do you measure the coefficient of friction experimentally?
By determining the ratio of frictional force to the normal force.
Inclined planes and force sensors are commonly used for such experiments.
How does lubrication affect the coefficient of friction?
It reduces the coefficient of friction by minimizing surface contact.
Lubricants are critical in mechanical and industrial applications.
Why does friction make it difficult to move heavy furniture?
The coefficient of static friction and normal force are high.
Using rollers or sliders reduces the effective coefficient of friction.
Fill in the blank:
Higher coefficients of friction result in ______ resistance to sliding.
greater
Materials like rubber on asphalt exhibit high coefficients of friction, enhancing grip.
Why is the coefficient of static friction crucial in load transportation?
It determines the force needed to initiate movement, ensuring loads remain stable during transportation.
Proper material choices reduce sliding accidents by optimizing static friction.
Why is the coefficient of friction important in designing vehicle tires?
It ensures sufficient grip and traction by optimizing the interaction between the tires and the road surface.
Tire tread patterns are designed to maximize the effective coefficient of friction under various conditions.
A sled is pulled across a horizontal surface with a normal force of 100 N and a frictional force of 25 N. What is the coefficient of kinetic friction?
μk=Ff/FN = 25/100 =0.25
The ratio of frictional force to normal force determines the coefficient.
A car skids to a stop on a wet road with a coefficient of kinetic friction of 0.4. If the car’s weight is 12,000 N, what is the frictional force?
Ff =(μk)⋅(FN) =(0.4)⋅(12,000N)=4,800N
The frictional force is directly proportional to the coefficient of friction and the normal force.
Explain how frictional forces impact athletic performance.
Friction affects grip and stability in sports, with higher friction aiding traction and lower friction enabling smoother motion, such as in skating.
Equipment like shoes and surfaces are tailored to optimize friction for specific sports.
