Linear Kinematics of Movement

Linear Motion

All points on the body move the same distance, same direction, same time.

Angular Motion

All points move in circles about a fixed axis. Examples: whole-body spin (ice skater), segment rotation (flexion, extension), external axis (child on swing).

General Motion

Combination of linear + angular motion. Most common. Examples: pedaling a bike, walking.

Descriptors of Linear Motion

Answer: How far? What direction? How fast? Speeding up/slowing down?

Scalar Variable

Defined by magnitude only. Examples: mass, distance, time, temperature, speed.

Vector Variable

Defined by magnitude + direction. Examples: displacement, velocity, acceleration.

Position

Location in space relative to a reference point (origin). Can be 1D, 2D, or 3D.

Distance (Scalar)

Length of path traveled.

Displacement (Vector)

Straight line change in position with direction.

Speed (Scalar)

Rate of motion = distance ÷ time.

Velocity (Vector)

Rate of motion = displacement ÷ time.

Instantaneous Speed/Velocity

Rate of motion at a very short instant (e.g., interval in a race).

Acceleration

Rate of change of velocity. Includes starts, stops, speeding up, slowing down, or direction change. Vector quantity.

Projectile

Body in free fall influenced only by gravity and air resistance.

Projectile Motion – Why separate horizontal & vertical?

Vertical motion is affected by gravity; horizontal motion is not. Vertical = height; horizontal = distance traveled.

Effect of Gravity

Constant downward acceleration of -9.81 m/s² near Earth’s surface.

Projectile Trajectory – Angle of Projection

Direction of launch determines trajectory shape. Too flat = common error in basketball shooting.

Projectile Trajectory – Projection Speed

Magnitude of launch velocity determines length/size of trajectory.

Air Resistance

Causes real-life trajectories to deviate from the perfect parabola.