🏎️Engineering Mechanics – Dynamics Unit 1 – Particle Kinematics

Key Concepts and Definitions

• Particle a body with a mass but negligible size and shape
• Kinematics the study of motion without considering the forces causing it
• Displacement the change in position of a particle measured from a reference point
• Velocity the rate of change of position with respect to time
  • Average velocity the displacement divided by the time interval
  • Instantaneous velocity the limit of the average velocity as the time interval approaches zero
• Acceleration the rate of change of velocity with respect to time
  • Average acceleration the change in velocity divided by the time interval
  • Instantaneous acceleration the limit of the average acceleration as the time interval approaches zero
• Speed the magnitude of the velocity vector

Coordinate Systems and Reference Frames

• Coordinate systems used to describe the position, velocity, and acceleration of a particle
  • Cartesian coordinate system (rectangular) uses three mutually perpendicular axes (x, y, z)
  • Cylindrical coordinate system uses a radial distance (r), an angle (θ), and a height (z)
  • Spherical coordinate system uses a radial distance (ρ), a polar angle (φ), and an azimuthal angle (θ)
• Reference frames the coordinate system in which motion is described
  • Fixed (inertial) reference frame a non-accelerating frame in which Newton's laws of motion are valid
  • Moving (non-inertial) reference frame a frame that accelerates relative to a fixed frame
• Origin the point from which coordinates are measured
• Orientation the direction of the coordinate axes relative to a fixed reference

Position, Velocity, and Acceleration

• Position vector ($\vec{r}$) describes the location of a particle relative to the origin of a coordinate system
  • Components of the position vector depend on the chosen coordinate system (Cartesian, cylindrical, or spherical)
• Velocity vector ($\vec{v}$) the rate of change of the position vector with respect to time
  • $\vec{v} = \frac{d\vec{r}}{dt}$
  • Components of the velocity vector depend on the chosen coordinate system
• Acceleration vector ($\vec{a}$) the rate of change of the velocity vector with respect to time
  • $\vec{a} = \frac{d\vec{v}}{dt}$
  • Components of the acceleration vector depend on the chosen coordinate system
• Tangential and normal components of acceleration
  • Tangential component ($a_t$) parallel to the velocity vector, representing changes in speed
  • Normal component ($a_n$) perpendicular to the velocity vector, representing changes in direction

Rectilinear Motion

• Motion along a straight line path
• Position, velocity, and acceleration are functions of time only
  • $x = f(t)$, $v = \frac{dx}{dt}$, $a = \frac{dv}{dt}$
• Kinematic equations for constant acceleration
  • $v = v_0 + at$
  • $x = x_0 + v_0t + \frac{1}{2}at^2$
  • $v^2 = v_0^2 + 2a(x - x_0)$
• Motion graphs (position-time, velocity-time, and acceleration-time) used to visualize and analyze motion
• Area under a velocity-time graph represents displacement
• Area under an acceleration-time graph represents change in velocity

Curvilinear Motion

• Motion along a curved path
• Position, velocity, and acceleration are vector quantities
  • Velocity vector is always tangent to the path
  • Acceleration vector has tangential and normal components
• Polar coordinates (r, θ) often used for planar curvilinear motion
  • Radial component of velocity ($v_r$) represents change in radial distance
  • Transverse component of velocity ($v_θ$) represents change in angular position
• Cylindrical coordinates (r, θ, z) used for three-dimensional curvilinear motion
• Projectile motion a special case of curvilinear motion under constant acceleration due to gravity
  • Horizontal and vertical components of motion can be analyzed separately
  • Range, time of flight, and maximum height can be determined using kinematic equations

Relative Motion Analysis

• Motion of a particle described relative to a moving reference frame
• Relative position vector ($\vec{r}_{B/A}$) the position of particle B relative to particle A
  • $\vec{r}_{B/A} = \vec{r}_B - \vec{r}_A$
• Relative velocity vector ($\vec{v}_{B/A}$) the velocity of particle B relative to particle A
  • $\vec{v}_{B/A} = \vec{v}_B - \vec{v}_A$
• Relative acceleration vector ($\vec{a}_{B/A}$) the acceleration of particle B relative to particle A
  • $\vec{a}_{B/A} = \vec{a}_B - \vec{a}_A$
• Translating reference frames relative motion analysis when the reference frame has a constant velocity
• Rotating reference frames relative motion analysis when the reference frame has a constant angular velocity
  • Coriolis acceleration an apparent acceleration experienced by a particle in a rotating reference frame
  • Centripetal acceleration the acceleration directed towards the center of rotation

Problem-Solving Techniques

• Identify the particle or particles of interest
• Choose an appropriate coordinate system and reference frame
• Draw free-body diagrams to visualize forces acting on the particle (if applicable)
• Determine the known and unknown quantities
• Apply the relevant kinematic equations or principles
  • Use calculus (integration and differentiation) when dealing with non-constant acceleration
• Solve for the unknown quantities
• Verify the results using dimensional analysis and physical intuition
• Interpret the results in the context of the problem

Real-World Applications

• Automotive engineering
  • Vehicle dynamics (acceleration, braking, cornering)
  • Suspension design
  • Collision analysis
• Aerospace engineering
  • Aircraft and spacecraft trajectory analysis
  • Orbital mechanics
  • Rocket propulsion
• Biomechanics
  • Human and animal motion analysis
  • Sports performance optimization
  • Prosthetic design
• Robotics
  • Robot arm motion planning
  • Mobile robot navigation
  • Control systems design
• Manufacturing
  • Machine tool motion control
  • Material handling systems
  • Vibration analysis and isolation