3.4.1.3
Terminal velocity is reached when drag equals weight
Motion Along a Straight Line — AQA A-Level Physics
Key Definition
Terminal velocity — The constant maximum velocity reached when the drag force on a falling object equals its weight, so the resultant force and acceleration are zero.
- A falling body accelerates due to gravity, increasing its speed.
- As speed increases, drag force increases.
- When $drag = weight$, the resultant force is zero and accelerationThe rate of change of velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. A vector quantity. Measured in m s⁻². stops.
- The object then falls at a constant speed: terminal velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.The constant velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹. reached when the driving force on an object is exactly balanced by resistive forces, so the resultant force is zero..
- On a velocity-time graph, terminal velocityThe constant velocity reached when the driving force on an object is exactly balanced by resistive forces, so the resultant force is zero. appears as a horizontal line after an initial curve.
- A heavier object reaches a higher terminal velocityThe constant velocity reached when the driving force on an object is exactly balanced by resistive forces, so the resultant force is zero. because it needs a greater drag force to balance its larger weight.
Common Mistake
MEDIUM
Students often: Don't say a skydiver moves upwards when they open their parachute.
Instead: The skydiver decelerates to a new, lower terminal velocity. They never move upwards -- they just slow down.
Instead: The skydiver decelerates to a new, lower terminal velocity. They never move upwards -- they just slow down.