A.1.1—Position, velocity and acceleration

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.

How it is assessed

The evidence uses a motion-path diagram and asks for the velocity vector at a point. The mark scheme rewards a tangent arrow with the correct direction and origin at the specified point.

Command terms

Label / Identify / Draw

What earns marks

When a diagram asks for velocity at a point on a path, draw the arrow tangent to the path, beginning at the stated point, and orient it in the direction of motion. Name the quantity and include direction whenever the question requires a vector.

Watch for

Drawing the velocity arrow radially or along the wrong chord instead of tangent to the path at the specified point.

Representative question

[Maximum number: 1]

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

A.1.1 Exam Analysis

Assessment in practice

Retrieve the A.1 Kinematics Model

Question 1