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Terminal velocity is the maximum constant velocity reached by a falling object when drag force equals weight, giving zero resultant force. Free notes.
Acceleration, Velocity-Time Graphs and Terminal Velocity (Part 3/3) is part of Forces and motion in GCSE AQA Higher Physics.
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Terminal velocity is the maximum constant velocity reached by a falling object when drag force equals weight, giving zero resultant force. Free notes.
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Use this lesson to stay inside Forces and motion while connecting the detail back to the wider Forces topic.
Read the core explanations from Acceleration, Velocity-Time Graphs and Terminal Velocity (Part 3/3) before testing yourself from memory.
Picture a skydiver jumping from a plane. At first, they accelerate downwards rapidly. But after falling for several seconds, something interesting happens - they stop accelerating and fall at a steady speed.
This steady speed is called terminal velocity. It's not a mysterious phenomenon - it's physics in action. When any object falls through a fluid (like air or water), two main forces compete against each other.
The first force is weight, pulling the object downwards with constant strength. The second is drag force, pushing upwards against the motion. Here's the key insight: drag force increases as the object moves faster.
When an object first starts falling, drag force is zero because the object isn't moving yet. Weight is the only force acting, so there's a large resultant force downwards. This creates maximum acceleration.
As the object speeds up, drag force grows stronger. The resultant force becomes smaller because drag opposes weight. Smaller resultant force means less acceleration - the object is still speeding up, but more slowly.
Eventually, drag force grows large enough to equal weight. When this happens, the resultant force becomes zero. No resultant force means no acceleration - the object continues falling at constant velocity.
This balance point is terminal velocity. The object has reached its maximum falling speed for those conditions. It will maintain this speed until something changes - like opening a parachute or hitting the ground.
Velocity-time graphs tell the complete story of terminal velocity. The shape reveals exactly what's happening to the forces at each moment during the fall.
At the start, the graph shows a steep positive gradient. This represents high acceleration because the resultant force is large (weight minus small drag force). The steeper the gradient, the greater the acceleration.
As time progresses, the gradient becomes less steep. The object is still accelerating, but the acceleration is decreasing. This happens because drag force is growing, reducing the resultant force.
Finally, the graph becomes horizontal - zero gradient means zero acceleration. The object has reached terminal velocity and will maintain this constant speed.
Worked example: Calculating Acceleration from a Velocity-Time Graph
A falling object has velocity 5 m/s at t = 2s and velocity 15 m/s at t = 6s. Calculate the acceleration during this time period.
Answer: 2.5 m/s²
Terminal velocity isn't the same for every object. Several factors determine how fast an object will fall when it reaches this balance point between weight and drag.
Mass plays a crucial role. Heavier objects have greater weight, so drag force must become larger to balance it. This means heavier objects reach higher terminal velocities. A bowling ball falls faster than a tennis ball.
Surface area affects drag force directly. Objects with larger surface areas experience more drag at any given speed. A feather has much more surface area per unit mass than a coin, so it reaches a much lower terminal velocity.
The fluid itself matters too. Denser fluids create more drag. An object falling through honey reaches terminal velocity much sooner and at a much lower speed than the same object falling through air.
Understanding terminal velocity explains many phenomena we observe in everyday life. Raindrops are a perfect example - they don't hit us at devastating speeds because they reach terminal velocity during their fall.
Small raindrops have low mass and relatively high surface area, giving them a terminal velocity of about 2-9 m/s. Without terminal velocity, raindrops falling from clouds at 2000m height would hit the ground at over 200 m/s - fast enough to cause serious injury.
Parachutes work by dramatically increasing surface area and drag force. This reduces terminal velocity from about 60 m/s (fatal) to about 5 m/s (survivable). The parachute doesn't slow the person down - it gives them a new, much lower terminal velocity.
Seeds and spores use terminal velocity for dispersal. Dandelion seeds have feathery structures that increase drag, allowing them to travel further on air currents before reaching the ground.
Terminal velocity questions often test your understanding of force balance and graph interpretation. Examiners frequently ask you to explain why terminal velocity occurs, not just what it is.
When describing terminal velocity, always mention that drag force equals weight, creating zero resultant force and zero acceleration. Many students forget to explain the force balance clearly.
Graph questions require you to identify the horizontal section as terminal velocity and explain that zero gradient means zero acceleration. Don't just state that the line is flat - explain what this means physically.
Common mistakes include thinking that terminal velocity means all forces stop acting, or that heavier objects always fall faster. Remember: at terminal velocity, forces are balanced, not absent. In a vacuum, all objects fall at the same rate regardless of mass.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Terminal velocity is the maximum constant velocity reached by a falling object when drag force equals weight, giving zero resultant force and zero acceleration. The object keeps falling, but at a constant speed.
Drag force is the force that opposes motion through a fluid, caused by friction between the object and fluid particles. It increases with speed and depends on the object's shape and surface area.
A parachute dramatically increases surface area and drag force, giving the person a new, much lower terminal velocity. It reduces terminal velocity from about 60 m/s, which is fatal, to about 5 m/s, which is survivable.
Heavier objects do not always fall faster: in a vacuum, all objects fall at the same rate regardless of mass. In air, heavier objects reach higher terminal velocities because a larger drag force is needed to balance their weight.
At first weight is the only force, so the resultant force and acceleration are at their maximum. As the object speeds up, drag force increases, the resultant force gets smaller and acceleration decreases. When drag equals weight, the resultant force is zero and the object falls at terminal velocity.
Terminal velocity depends on mass, surface area and the fluid. Heavier objects have greater weight, so they reach higher terminal velocities; larger surface areas give more drag and lower terminal velocities; and denser fluids, like honey, give much lower terminal velocities.
Raindrops do not hit at devastating speeds because they reach terminal velocity, about 2–9 m/s for small drops. Without terminal velocity, raindrops falling 2000 m would hit the ground at over 200 m/s, fast enough to cause serious injury.
Two main forces act on an object falling through a fluid: weight pulling it downwards with constant strength, and drag force pushing upwards against the motion. Drag increases as the object moves faster.
The velocity-time graph of a falling object starts with a steep positive gradient, showing high acceleration, then becomes less steep as drag grows, and finally becomes horizontal. Zero gradient means zero acceleration: the object has reached terminal velocity.
A falling object's acceleration decreases because drag force grows as it speeds up, reducing the resultant force. Smaller resultant force means less acceleration, so the object still speeds up but more slowly, until drag equals weight.
Heavier objects reach higher terminal velocities, because their greater weight needs a larger drag force to balance it. A bowling ball falls faster than a tennis ball.
Denser fluids create more drag, so an object falling through honey reaches terminal velocity much sooner and at a much lower speed than the same object falling through air.
Dandelion seeds have feathery structures that increase drag, giving them a low terminal velocity. This lets them travel further on air currents before reaching the ground, which helps dispersal.
Forces do not stop acting at terminal velocity; they are balanced, not absent. Drag force equals weight, so the resultant force is zero and the acceleration is zero.
A falling object whose velocity goes from 5 m/s at 2 s to 15 m/s at 6 s has an acceleration of 2.5 m/s². Δv = 15 − 5 = 10 m/s and Δt = 6 − 2 = 4 s, so a = 10 ÷ 4 = 2.5 m/s².