Essential Physics Definitions: Motion and Friction Explained

Fundamental Definitions in Kinematics

Define any three of the following terms: a) Velocity, b) Acceleration, c) Uniform acceleration, d) Variable acceleration, e) Rectilinear motion, f) Static friction, g) Dynamic friction.

• a) Velocity: The velocity of a body is its speed in a given direction.
• b) Acceleration: The rate of change of velocity over time.
  • Formula: a = (v - u) / t
  • a = acceleration in m/s²
  • v = final velocity in m/s
  • u = initial velocity in m/s
  • t = time taken in seconds (s)
• c) Uniform Acceleration: If the velocity of a body changes by an equal amount in equal intervals of time, however small the interval may be, its acceleration is said to be uniform.
• d) Variable Acceleration: When changes in the velocity of an object are not the same at equal time intervals, it is said to be variable acceleration.
• e) Rectilinear Motion: If a particle is restricted to move along a straight line, its motion is called rectilinear (or linear) motion. Such motion can be described using one coordinate only.
• f) Static Friction: Friction experienced by a body when it is at rest.
• g) Dynamic Friction: Friction experienced by a body when it is in motion.

Friction and Surface Mechanics

Define any four of the following terms: A) Limiting force of friction, B) Coefficient of friction, C) Angle of friction, D) Angle of repose, E) Cone of friction.

What is Friction?

When a body slides or tends to slide on a surface on which it is resting, a resisting force opposing the motion is produced at the contact surface. This resisting force is called Friction or Friction Force.

Key Friction Concepts

• Limiting Friction: The maximum friction force that can be developed at the contact surface when a body is just on the point of moving.
• Coefficient of Friction (μ): The ratio of limiting friction (F) to the normal reaction (N).
  • Formula: μ = F / N or F = μN
  • μk = coefficient of kinetic friction
  • μs = coefficient of static friction
• Angle of Friction: The angle between the normal reaction (N) and the resultant force (R). It is also called the limiting angle of friction.
• Angle of Repose: With an increase in the angle of an inclined surface, the maximum angle at which a body starts sliding down is called the angle of repose.