Equations of motion — common mistakes

When dealing with vertical motion, always establish a positive direction (e.g., upwards or downwards) and stick to it! If upwards is positive, then 'g' will be $-9.81 \, \text{m/s}^2$ for an object falling down.

For projectile motion, break the initial velocity into horizontal and vertical components using trigonometry. Treat each component as a separate 1D problem, but remember they share the same time of flight!

Speed is a scalar quantity that only describes how fast an object is moving (its magnitude). Velocity is a vector quantity that describes both how fast an object is moving and in what direction. For example, '30 m/s' is a speed, while '30 m/s East' is a velocity.

You can use the SUVAT equations only when an object is moving with uniform (constant) acceleration in a straight line. They are not applicable if the acceleration is changing or if the motion is not linear (e.g., circular motion).

Negative values indicate that the quantity is in the opposite direction to the one you defined as positive. For example, if 'upwards' is positive, a negative displacement means the object is below its starting point, and a negative velocity means it's moving downwards.