Thẻ ghi nhớ: Chapter 6: Force and motion -II | Quizlet

Static Friction ($f_s$)

The force that opposes the initial motion of an object relative to a surface, varying in magnitude up to a maximum value.

Kinetic Friction ($f_k$)

The friction force that acts between moving surfaces, typically having a nearly constant magnitude for a given pair of surfaces.

Relationship between static friction and applied force ($F_{app}$)

As long as the object does not move, the static friction force is equal in magnitude and opposite in direction to the component of the applied force parallel to the surface ($f_s = F_{app}$).

Maximum Static Friction Formula

The upper limit of the static friction force magnitude, calculated by the equation f_{s,max} = \μ_s F_N.

Kinetic Friction Formula

The constant magnitude of kinetic friction, calculated by the equation f_k = \μ_k F_N.

Coefficient of Static Friction (\μ_s)

A dimensionless constant that depends on the materials and properties of the two contacting surfaces.

Coefficient of Kinetic Friction (\μ_k)

A dimensionless constant associated with the friction between surfaces in relative motion.

Comparison of Friction Coefficients

For a given pair of surfaces, the coefficient of static friction is generally greater than the coefficient of kinetic friction (\μ_s > \μ_k).

Role of Normal Force ($F_N$) in Friction

Both static and kinetic friction magnitudes are directly proportional to the magnitude of the normal force pressing the surfaces together.

Surface Area Independence

To a good approximation, the friction force between two surfaces is independent of the macroscopic area of contact between them.

Cold Welding

The process where microscopic contact points between two surfaces bond together, contributing to the origin of friction.

Drag Force ($D$)

The resistive force encountered by an object moving through a fluid like air or water.

Drag Force Equation

The magnitude of the drag force for high-speed motion through air, given by D = \frac{1}{2} C \ρ A v^2.

Drag Coefficient ($C$)

A dimensionless value determined experimentally that characterizes the aerodynamic properties of an object’s shape.

Terminal Speed ($v_t$)

The constant speed reached by a falling object when the magnitude of the upward drag force equals the magnitude of the downward gravitational force.

Terminal Speed Formula

The mathematical expression for terminal speed: v_t = \sqrt{\frac{2F_g}{C \ρ A}}.

Uniform Circular Motion

Motion along a circular path at a constant speed, requiring a net force directed toward the center of the circle.

Centripetal Acceleration ($a$)

The acceleration experienced in uniform circular motion, calculated as $a = \frac{v^2}{R}$.

Centripetal Force ($F_{net}$)

The name given to the net force causing centripetal acceleration, satisfying the relationship $F_{net} = \frac{mv^2}{R}$.

Centripetal Force Direction

The net force in uniform circular motion is always directed radially inward toward the center of the circular path.

Period of Revolution ($T$)

The time taken for an object to complete one full revolution in a circular path.

Relationship Between Speed and Period

For an object in uniform circular motion, the speed is related to the period by the formula v = \frac{2 \π R}{T}.

Centripetal Force on a Flat Curve

On a flat road, the required centripetal force for a turning vehicle is provided by the static friction between the tires and the road.

Purpose of a Banked Curve

To use a component of the normal force to provide centripetal force, reducing the dependence on friction to navigate a turn safely.

Net Force at Terminal Velocity

At terminal velocity, the net force on the object is zero ($F_{net} = 0$), as drag and gravity are perfectly balanced.