EduNinja

Choose a reference

Position $\vec r$ specifies where an object is relative to a chosen origin. A position is not meaningful without a reference frame and coordinate direction.

Track change in position

Velocity $\vec v$ describes how position changes with time. It is a vector: its direction is the direction of motion at that instant, and on a curved path the velocity arrow is tangent to the path.

Track change in velocity

Acceleration $\vec a$ describes how velocity changes with time. A change in speed, direction, or both is acceleration; an object can accelerate even while its instantaneous speed is zero.

Common trap

Do not use “velocity” as a synonym for speed. Speed gives only magnitude; velocity also requires direction relative to the chosen coordinate system.

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the velocity of the ball at P . Label this arrow v.

Describe motion

Position locates the object, velocity is the rate of change of position, and acceleration is the rate of change of velocity. Distance and speed are scalar; displacement and velocity are directed quantities.

Use the right model

For uniform acceleration:

$v=u+at,\quad s=ut+ rac12at^2,\quad v^2=u^2+2as$

For projectiles without drag, solve horizontal and vertical components with a shared time. Do not use these equations when acceleration is non-uniform.

Check the boundary

Ask whether the quantity is average or instantaneous, whether the route or endpoints matter, whether acceleration is constant, and whether a neglected force such as drag changes the model.

A.1.1—Position, velocity and acceleration

Describe Motion with Position, Velocity and Acceleration

Retrieve the A.1 Kinematics Model

A.1.1 Exam Analysis