HomeConcept libraryFluidsFluid and Pressure

FluidsIntroStarter track

Concept module

Drag and Terminal Velocity

Drop one body through a fluid and use mass, area, and drag strength to see drag grow with speed until force balance settles into terminal velocity.

Interactive lab

Keep the stage, graph, and immediate control feedback in one working view.

Time

0.00 s / 4.00 sLivePause to inspect a specific moment, then step or scrub through it.

0.00 s4.00 s

Drag and Terminal Velocity

Release one object into one fluid. Mass sets the constant weight, area and drag strength set how quickly drag grows with speed, and the fall settles when those forces nearly balance.

Graphs

Switch graph views without breaking the live stage and time link.

Speed vs time

The speed curve rises quickly at first and then levels toward the flat terminal-speed line because drag is catching up to the weight.

time (s): -0.32 to 4.32speed (m/s): -0.46 to 6.17

SpeedTerminal speed

Hover or scrub to link the graph back to the stage.time (s) / speed (m/s)

Controls

Adjust the physical parameters and watch the motion respond.

Mass

m

2 kg

Changes the constant weight that drag eventually has to balance.

Area

A

0.05 m^2

Changes how much drag the object gets at the same speed.

Drag strength

k

Lumped fluid-and-shape drag constant for this bounded page.

More tools

Secondary controls, alternate presets, and less-used toggles stay nearby without crowding the main bench.

Show

More presets

Presets

Predict -> manipulate -> observe

Keep the active prompt next to the controls so each change has an immediate visible consequence.

ObservationPrompt 1 of 3

Right after release the object is not already at terminal speed because drag depends on speed. At very small

v

, the drag arrow is still much smaller than the constant weight arrow.

Equation map

See each variable before you move it.

Select a symbol to highlight the matching control and the graph or overlay it most directly changes.

m

Mass

2 kg

Raises the constant weight. With the same area and drag strength, the object must reach a higher speed before drag can balance it.

Graph: Speed vs timeGraph: Terminal speed vs massOverlay: Force balanceOverlay: Terminal-speed cue

Equations in play

Choose an equation to sync the active symbol, control highlight, and related graph mapping.

More tools

Detailed noticing prompts, guided overlays, and challenge tasks stay available without taking over the main bench.

Hide

What to notice

Keep one force question live at a time so the stage, the time rail, and the graphs stay tied to the same fall.

ObservationPrompt 1 of 3

Graph: Speed vs time

Right after release the object is not already at terminal speed because drag depends on speed. At very small

v

, the drag arrow is still much smaller than the constant weight arrow.

Graph: Speed vs timeGraph: Force balance vs timeOverlay: Force balanceEquation

A

Equation

k

Guided overlays

Focus one overlay at a time to see what it represents and what to notice in the live motion.

3 visible

Overlay focus

Force balance

Shows the constant weight arrow, the upward drag arrow, and the shrinking net-force arrow.

What to notice

The weight arrow hardly changes, but the drag arrow grows with speed until the two nearly match.

Why it matters

It keeps terminal velocity tied to force balance instead of treating it like a memorized speed limit.

Control: MassControl: AreaControl: Drag strengthGraph: Force balance vs timeGraph: Speed vs timeEquation

m

Equation

A

Equation

k

Challenge mode

Use the same falling-body bench for compact terminal-speed targets. The checks read the real force balance and live speed instead of a detached puzzle state.

0/2 solved

ConditionStretch

2 of 6 checks

Freeze the near-terminal moment

Starting from Draggy disk, pause when the object is effectively at terminal speed: drag nearly equals weight and the remaining net downward force is tiny.

Inspect timeGraph-linkedGuided start2 hints

Suggested start

Pause the fall and scrub until the drag and weight are almost matched.

Pending

Open the Force balance vs time graph.

Speed vs time

Matched

Keep the Force balance visible.

Matched

Keep the Terminal-speed cue visible.

Pending

Pause into inspect mode.

live

Pending

Make the net downward force smaller than about

0.35 N

19.6 N

Pending

Bring the current speed within about

0.10 m/s

of terminal speed.

5.72 m/s

The checklist updates from the live simulation state, active graph, overlays, inspect time, and compare setup.

At t = 0 s, the object has fallen 0 m and is moving at 0 m/s. Weight is 19.6 N, drag is 0 N, and the terminal speed for this setup is 5.72 m/s. The object is still in the early part of the fall where drag is much smaller than weight.

Equation detailsDeeper interpretation, notes, and worked variable context.

Quadratic drag for this bounded model

The upward resistive force grows with speed, area, and the lumped drag-strength constant.

F_{d} = k A v^{2}

A

Area 0.05 m^2

k

Drag strength 12

Weight

Gravity keeps the downward weight essentially constant while the object falls.

W = m g

m

Mass 2 kg

Force balance at terminal speed

Terminal speed is the speed where drag has grown enough to match the weight.

k A v_{t}^{2} = m g

m

Mass 2 kg

A

Area 0.05 m^2

k

Drag strength 12

Terminal-speed formula

A larger mass raises terminal speed, while a larger area or stronger drag lowers it.

v_{t} = \frac{m g}{k A}

Here $k$ packages the fluid-and-shape details so the page can stay focused on one compact drag model.

m

Mass 2 kg

A

Area 0.05 m^2

k

Drag strength 12

Progress

Not startedMastery: NewLocal-first

Start exploring and Open Model Lab will keep this concept's progress on this browser first. Challenge mode has 2 compact tasks ready. No finished quick test, solved challenge, or completion mark is saved yet.

Let the live model runChange one real controlOpen What to notice

Try this setup

Copy the live bench state and reopen this concept with the same controls, graph, overlays, and compare context.

Stable links

Starter track

Step 5 of 50 / 5 complete

Fluid and Pressure

Earlier steps still set up Drag and Terminal Velocity.

1. Pressure and Hydrostatic Pressure2. Continuity Equation3. Bernoulli's Principle4. Buoyancy and Archimedes' Principle+1 more steps

Previous step: Buoyancy and Archimedes' Principle.

Start from track beginning

Short explanation

What the system is doing

This page keeps drag bounded and honest by following one object released from rest through one fluid. Weight stays constant at $m g$ , while the upward resistive force grows with speed according to the compact rule $F_{d} = k A v^{2}$ . That makes the motion neither constant-acceleration free fall nor a full fluid-dynamics sandbox.

Terminal velocity is the balance point, not a mystery cap on motion. As the object speeds up, the drag arrow grows until it nearly matches the weight arrow. At that stage the net force shrinks toward zero, so the acceleration collapses and the speed levels off even though the object keeps moving downward.

Mass, area, and drag strength matter in different ways. More mass raises the weight that drag must match, so the terminal speed is higher. More area or stronger drag makes the same speed produce a larger resistive force, so the balance happens sooner and at a lower speed. This bounded model keeps gravity fixed, folds fluid-and-shape details into one drag-strength constant $k$ , and ignores buoyancy so the force story stays compact and readable.

Key ideas

01Drag depends on speed in this bench, so it starts small right after release and grows rapidly as the object speeds up.

02Weight stays constant while drag changes, which is why the net force is largest early and much smaller later in the fall.

03Terminal velocity means drag and weight are balancing so the net force is near zero. It does not mean the object has stopped moving.

04A larger mass raises terminal speed, while a larger area or stronger drag lowers terminal speed because those settings change how quickly drag catches up to weight.

Live drag checks

Solve the exact state on screen.

Use the live bench directly. The current controls set the terminal-speed prediction, and the current time on the rail sets the live force-balance example.

Live valuesFollowing current parameters

For the current setup with $m = 2$ , $A = 0.05$ , and $k = 12$ , what terminal speed does the bounded drag model predict?

m

Mass

2 kg

A

Area

0.05 m^2

k

Drag strength

W

Weight

19.6 N

1. Turn mass into the constant downward weight

With gravity fixed on this page, the current setup gives

W = m g = 19.6 N

2. Use the terminal-speed balance condition

Terminal speed is where drag catches the weight, so

k A v_{t}^{2} = m g

with

k = 12

and

A = 0.05 m^{2}

3. Solve for the resulting balance speed

That gives

v_{t} = m g / (k A) = 5.72 m/s

for the current controls.

Current terminal speed

W = 19.6 N, v_{t} = 5.72 m/s

This setup sits in the middle, so the balance speed is neither especially low nor especially high.

Terminal-speed checkpoint

Two objects use the same drag strength and the same frontal area, but one has twice the mass. Which one has the higher terminal speed?

Prediction prompt

Decide whether the heavier object balances drag sooner or later.

Check your reasoning

The heavier object has the higher terminal speed.

The heavier object has a larger constant weight. Drag has to grow to a larger value before it can balance that weight, so the speed at balance is higher.

Common misconception

Terminal velocity happens because gravity turns off once the object has been falling for a while.

Gravity does not disappear. The weight force stays essentially constant throughout this page.

What changes is the drag force. It grows with speed until it almost matches the weight, so the net downward force becomes very small.

Quick test

Variable effect

Question 1 of 5

Use the force story, not just the formula. Each question checks whether the drag-balance picture is stable enough to explain the graphs.

At the same mass and drag strength, what does a larger area do to terminal speed?

Choose one answer to reveal feedback, then test the idea in the live system if a guided example is available.

Accessible description

The simulation shows one object dropping through one fluid column with a distance ruler on the left and a readout card on the right. The object changes width with area, while mass is represented through the force readouts rather than by resizing the object itself. Optional overlays show a constant downward weight arrow, an upward drag arrow that grows with speed, a net-force arrow, a terminal-speed cue, and a distance guide.

The time rail controls one bounded fall from rest over four seconds. Compare mode can ghost a second setup behind the current one so two force-balance stories stay on the same scale.

The readout card reports mass, area, drag strength, distance fallen, current speed, terminal speed, drag force, and net downward force.

Graph summary

The speed-history graph is the main motion graph. The speed curve rises and then flattens toward the constant terminal-speed line.

The force-balance graph keeps the forces honest: weight stays flat, drag rises, and the net downward force shrinks toward zero.

The three response graphs isolate mass, area, and drag strength. The mass sweep rises, while the area and drag-strength sweeps fall because larger drag-side factors lower terminal speed.

Bridge mechanics and fluids next

Keep moving through the concept map.

These suggestions come from the concept registry, so the reason label reflects either curated guidance or the fallback progression logic.

Compare free-flight and drag-limited motionMechanics

Drag and Terminal Velocity

See each variable before you move it.

Force balance

Freeze the near-terminal moment

Fluid and Pressure

What the system is doing

Solve the exact state on screen.

For the current setup with m=2, A=0.05, and k=12, what terminal speed does the bounded drag model predict?

At the same mass and drag strength, what does a larger area do to terminal speed?

Keep moving through the concept map.

Projectile Motion

Continuity Equation

Bernoulli's Principle

For the current setup with $m = 2$ , $A = 0.05$ , and $k = 12$ , what terminal speed does the bounded drag model predict?