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Flip to reveal answersWhat is drag (fluid resistance)?
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All 11 Flashcards — Fluid resistance and terminal velocity
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Question
What is drag (fluid resistance)?
Answer
A friction-like force from the air or liquid an object moves through. It always acts **against the motion** and **grows with speed**.
Question
Define terminal velocity.
Answer
The **constant** velocity a falling object reaches when the **drag equals its weight**, so the resultant force (and acceleration) is zero.
Question
What happens to drag as a falling object speeds up?
Answer
It **increases** — drag grows with speed.
Question
What is the condition for terminal velocity?
Answer
**Drag = weight** → resultant force = 0 → acceleration = 0.
Question
At terminal velocity, what is the resultant force?
Answer
**Zero** — weight and drag are equal and opposite, so they cancel.
Question
Does constant terminal velocity mean there are no forces?
Answer
**No** — weight and drag both act; they are **balanced**, so they cancel.
Question
How does the v–t graph of a falling body with air resistance look?
Answer
It **starts steep**, then **bends over and goes flat** — the flat value is the terminal velocity.
Question
What is the acceleration like just after release vs at terminal velocity?
Answer
Just after release it is **near g** (drag tiny); at terminal velocity it has fallen to **zero**.
Question
Formula for weight (given in the data booklet)?
Answer
$F_g = mg$ — mass × gravitational field strength.
Question
Throw a ball up with air resistance: how does the peak height compare to a vacuum?
Answer
**Lower** — going up, drag adds to gravity, so the ball decelerates faster and rises less far.
Question
Does air resistance change an object's weight as it falls?
Answer
**No** — the weight stays mg the whole way down; it is the **drag** that grows to match it.
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Kinematics
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