is the force that opposes motion between surfaces in contact. It's crucial for everyday activities like walking and driving, but can also hinder movement in machines. Understanding is key to solving real-world physics problems.
prevents objects from starting to move, while opposes motion once it begins. These forces depend on surface characteristics, material properties, and environmental factors. Mastering friction concepts helps in analyzing complex mechanical systems and predicting object behavior.
Friction
Principles of friction in physics
Friction opposes relative motion between two surfaces in contact
Acts parallel to surfaces and opposite to direction of motion or attempted motion
Converts kinetic energy into thermal energy (heat)
Caused by interactions between microscopic irregularities () on surfaces
Asperities interlock and resist motion
Crucial role in everyday life
Enables walking, running, and driving without slipping
Allows objects to remain stationary on inclined surfaces (ramps, hills)
Necessary for operation of mechanical devices (brakes, clutches)
Static vs kinetic friction
prevents an object from starting to move when force is applied
Acts when there is no relative motion between surfaces
fs proportional to N and μs: fs≤μsN
If applied force is less than maximum static friction force, object will not move
opposes motion of an object once it starts moving
Acts when there is relative motion between surfaces
Kinetic friction force fk proportional to normal force N and μk: fk=μkN
Coefficient of kinetic friction typically less than for same surfaces (rubber on concrete)
Transition from static to kinetic friction occurs when applied force exceeds maximum static friction force
Object starts to move, friction force drops from maximum static to kinetic friction force
Friction in Newtonian mechanics
Solving problems involving friction using ###'s_Laws_0###:
Identify surfaces in contact and determine direction of friction force
Draw with normal force, friction force, and other forces acting on object
Apply Newton's second law (∑F=ma) to object, considering force components parallel and perpendicular to surface
Use appropriate friction coefficient (static or kinetic) to relate friction force to normal force
Solve resulting equations for desired quantities (acceleration, maximum angle before sliding)
Example: Object on an (ramp)
Normal force N perpendicular to surface, given by N=mgcosθ (θ is angle of inclination)
Friction force f acts parallel to surface and opposite to direction of motion (or attempted motion)
Component of object's weight parallel to surface is mgsinθ
Apply Newton's second law to determine acceleration or maximum angle of inclination before object starts to slide
Factors affecting friction
Surface characteristics
Roughness of surfaces in contact (affects interlocking of asperities)
between surfaces (surprisingly, friction is generally independent of apparent contact area)
Material properties
Hardness and elasticity of materials (influence of surfaces)
Chemical composition (affects between surfaces)
Environmental factors
Presence of contaminants or lubricants ( can significantly reduce friction)
Temperature (can affect material properties and lubricant viscosity)
Type of motion
Sliding friction vs. (rolling friction is typically much lower than sliding friction)
Key Terms to Review (37)
Adhesion: Adhesion is the intermolecular force that causes two surfaces or materials to cling together. It is a fundamental concept in the study of friction, as adhesion contributes to the frictional force between surfaces in contact.
Amontons: Amontons is a key concept in the study of friction, which refers to the work of French physicist Guillaume Amontons. His findings laid the foundation for our understanding of the fundamental principles governing the frictional forces between surfaces in contact.
Artificial joint: An artificial joint is a synthetic implant used to replace a damaged natural joint in the human body, commonly due to arthritis or injury. These implants are designed to mimic the function and movement of a natural joint.
Asperities: Asperities refer to the microscopic irregularities or high points on the surface of two contacting materials. These surface imperfections play a crucial role in the frictional forces that arise between the interacting surfaces.
Coefficient of Friction: The coefficient of friction is a dimensionless scalar quantity that describes the ratio of the frictional force between two surfaces to the normal force pressing them together. It is a crucial parameter in understanding the behavior of objects sliding or rolling on surfaces, as well as in the analysis of centripetal forces.
Coefficient of Friction (μ): The coefficient of friction, denoted by the Greek letter μ, is a dimensionless scalar quantity that describes the ratio of the frictional force between two surfaces to the normal force pressing them together. It is a fundamental parameter in the study of friction, which is a crucial concept in both the topics of 6.2 Friction and 16.3 Wave Speed on a Stretched String.
Coefficient of kinetic friction: The coefficient of kinetic friction is a dimensionless constant that represents the ratio of the force of kinetic friction between two bodies in relative motion to the normal force pressing them together. It is denoted by $\mu_k$.
Coefficient of static friction: The coefficient of static friction is a dimensionless scalar that represents the ratio of the maximum static frictional force between two surfaces to the normal force pressing them together. It quantifies how difficult it is to start moving an object at rest.
Coefficient of Static Friction: The coefficient of static friction is a dimensionless quantity that represents the ratio of the maximum force of static friction between two surfaces to the normal force acting on them. It is a measure of the resistance to sliding motion between the surfaces when they are at rest relative to each other.
Contact Area: Contact area refers to the surface or region where two objects or surfaces come into direct physical contact with each other. It is an important concept in the study of friction, as the contact area between surfaces can significantly influence the frictional forces acting between them.
Coulomb: The Coulomb is the base unit of electric charge in the International System of Units (SI). It is named after the French physicist Charles-Augustin de Coulomb, who pioneered the study of electrostatic forces and their relationship to electric charge.
Coulomb's Law of Friction: Coulomb's law of friction is a fundamental principle that describes the frictional force between two surfaces in contact. It establishes a relationship between the normal force acting on the surfaces and the coefficient of friction, which determines the magnitude of the frictional force.
Deformation: Deformation is the change in shape or size of an object due to applied forces. It can be temporary (elastic) or permanent (plastic) based on the material properties and magnitude of the force.
Deformation: Deformation is the change in the shape or size of an object due to the application of a force or stress. It is a fundamental concept in physics that describes how materials respond to external forces, and it is essential for understanding various topics, including friction, collisions, and the behavior of solids under stress.
Free-body diagram: A free-body diagram is a graphical representation used to visualize the forces acting on an object. Each force is represented by an arrow pointing in the direction of the force with its length proportional to the magnitude.
Free-Body Diagram: A free-body diagram is a visual representation of an object or system that shows all the external forces acting on it. It is a fundamental tool used in physics to analyze the forces acting on an object and to solve problems involving Newton's laws of motion.
Friction: Friction is the resistive force that opposes the relative motion or tendency of such motion of two surfaces in contact. It acts parallel to the surfaces and opposite to the direction of motion.
Friction: Friction is a force that opposes the relative motion between two surfaces in contact. It arises due to the microscopic irregularities on the surfaces, which create resistance to sliding or rolling. Friction is a fundamental concept in physics that plays a crucial role in various topics, including solving problems, understanding forces, and analyzing energy transformations.
Frictional Force: Frictional force is the force that opposes the relative motion between two surfaces in contact with each other. It arises from the microscopic irregularities and interactions between the surfaces, and acts to resist the sliding or rolling of one surface over another.
Inclined plane: An inclined plane is a flat surface tilted at an angle to the horizontal. It is used to facilitate raising or lowering a load with less effort.
Inclined Plane: An inclined plane is a flat surface that is tilted or angled relative to the horizontal. It is a simple machine that is used to lift or move objects by applying a force parallel to the surface, rather than perpendicular to it. The inclined plane is a fundamental concept in physics, with applications across various topics.
Joule: A joule is the SI unit of work or energy, equivalent to one newton-meter. It represents the amount of work done when a force of one newton displaces an object by one meter in the direction of the force.
Joule: The joule (J) is the standard unit of energy in the International System of Units (SI). It represents the amount of work done or energy expended when a force of one newton acts through a distance of one meter.
Kinetic friction: Kinetic friction is the force that opposes the relative motion of two surfaces sliding past each other. It acts parallel to the surfaces in contact and depends on the nature of the materials and normal force.
Kinetic Friction: Kinetic friction is the force that opposes the relative motion between two surfaces in contact. It acts in the direction opposite to the direction of motion, and its magnitude is independent of the area of contact between the surfaces.
Lubrication: Lubrication is the process of reducing friction between two surfaces in contact by introducing a lubricating substance, such as oil or grease, between them. It is a critical concept in the study of friction, as it can significantly impact the behavior and efficiency of mechanical systems.
Lubrication helps minimize wear and tear, decrease energy consumption, and improve the overall performance of moving parts by creating a thin film that separates the surfaces and reduces the force required to overcome friction.
Maximum Static Friction Force: The maximum force that can be exerted on an object before it begins to slide relative to the surface it is in contact with. This force is the upper limit of the static friction force that can be applied before the object transitions from a stationary state to a sliding motion.
Newton: Newton is the standard unit of force in the International System of Units (SI), named after the renowned English physicist and mathematician, Sir Isaac Newton. It is a fundamental unit that is essential in understanding and describing the behavior of objects under the influence of various forces, as well as in the study of mechanics, dynamics, and other related areas of physics.
Newton's Laws: Newton's laws are a set of three fundamental principles that describe the relationship between an object and the forces acting upon it, governing the motion of physical bodies. These laws form the foundation of classical mechanics and are essential for understanding and solving problems in physics.
Normal Force: Normal force is the support force exerted by a surface perpendicular to the object resting on it, preventing the object from falling through the surface. It plays a crucial role in balancing other forces acting on an object, particularly in scenarios involving gravity and acceleration.
Rolling Friction: Rolling friction is the force that resists the motion of a rolling object, such as a wheel or a ball, as it rolls on a surface. It arises from the deformation of the surface and the object, as well as from the energy dissipated during the rolling process.
Static friction: Static friction is the force that resists the initiation of sliding motion between two surfaces in contact. It acts when an object is at rest relative to a surface and prevents it from moving.
Static Friction: Static friction is the force that acts between two surfaces in contact with each other, preventing them from sliding relative to one another. It arises from the microscopic irregularities on the surfaces and the adhesive forces between them, and it opposes the tendency of the surfaces to slide.
Surface Roughness: Surface roughness refers to the microscopic irregularities or unevenness present on the surface of a material. It is a measure of the texture and topography of a surface, which can have significant impacts on various physical and functional properties of the material.
Tribometer: A tribometer is an instrument used to measure the frictional properties of surfaces in contact, such as the coefficient of friction between two materials. It is a crucial tool in the study of tribology, which is the science of interacting surfaces in relative motion and the practices related to them.
μk: The coefficient of kinetic friction, μk, is a dimensionless quantity that represents the ratio of the force of kinetic friction between two surfaces in contact to the normal force pressing them together. It is a measure of the frictional force that opposes the relative motion between two surfaces as they slide against each other.
μs: μs, or the Greek letter mu followed by the lowercase letter s, is a unit of time used to measure very short durations, specifically microseconds. A microsecond is one-millionth of a second, or 0.000001 seconds. This unit is commonly used in the context of physics, particularly when discussing the dynamics of objects and the timescales involved in various physical processes.