Kinematics of a Particle

Curvilinear motion describes an object moving along a curved path. A car on a winding road is a clear example. The object’s position is shown with a position vector in a fixed frame of reference. The unit vector for that position comes from the position vector divided by its magnitude.

As the object moves, its position changes with time. The velocity vector is found by taking the time derivative of the position vector. In a fixed frame of reference, the directions of the unit vectors do not...

Projectile motion in a soccer kick shows how a ball travels through the air after it is launched. The launch angle, which is the angle of the kick, plays a major role in shaping the path of the ball. Once the ball is in the air, gravity is the only force acting on it.

The ball’s motion can be split into two independent velocity components: horizontal and vertical. The horizontal motion comes from the initial kick and stays at a constant velocity during the flight. Kinematics equations in the...

Curved path motion is described with tangential and normal axes. These car-centered coordinates move with the vehicle as it travels. The t-axis points in the direction of increasing position along the curved path. The n-axis is perpendicular to the t-axis and points toward the center of curvature.

The path can be split into tiny arc segments. Each segment matches part of a circle with a radius of curvature and a center of curvature. The positive n-direction uses the unit vector u n . This...

Polar coordinates describe curvilinear motion using a radial distance and an angle. The radial coordinate, r, extends from a fixed origin to the particle. The angular coordinate, θ, is measured in radians. It gives the counterclockwise angle between a fixed reference line and the radial line to the particle.

The particle’s position is written with a unit vector in the radial direction. Taking the time derivative of that position gives the velocity. That velocity has two parts. One is radial,...