1. Fluids
Liquids and gases that can flow are called fluids.
Fluid speed & pressure
Faster flow → lower pressure; wing lift examples.
Pressure (junior)Solid, liquid, atmospheric pressure and fluids.
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Fluid speed & pressure
Faster flow → lower pressure. Papers move together when you blow between them; cambered wings produce lift. Keep it qualitative for junior high and link to sprays and hydrofoils.
Memory cue: faster flow → lower P · papers close · wing lift from ΔP.
Key formulas
faster flow → lower Plift from ΔP across the wing
How to use
- Read the qualitative Related knowledge.
- Increase flow in papers mode; watch the gap close.
- Switch to airfoil; compare lift and weight; link to apps.
Read next
Related knowledge
Faster flow → lower pressure. Check with classroom demos, then wing lift and everyday uses.
2. Speed and pressure
- In a fluid, faster flow → lower pressure; slower flow → higher pressure.
3. Classroom checks
- Blow between two sheets of paper — they move together.
- Blow between two ping-pong balls — they move together.
- Blow above a paper strip — it lifts upward.
4. Wing lift
A cambered wing (curved on top, flatter below): faster flow and lower pressure above, slower flow and higher pressure below. The pressure difference makes upward lift. Lift greater than weight → the plane climbs.
5. Other applications
- Hydrofoils: wing-like foils lift the hull out of the water to cut drag.
- Spinning balls (curve / banana shots): different flow speeds on each side bend the path.
- Simple spray bottles: blow across a tube — fast flow, low P, draws liquid up and sprays it.
- Extension: full Bernoulli waits for later courses; junior focus is fast flow → low pressure.
Applications
- Airplane wings create lift from pressure differences due to flow speed.
- Atomizers and curved ball trajectories relate to flow–pressure effects.
FAQ
Why do the papers move together?
Fast flow between them lowers pressure; outside air pushes them in.
How does a wing get lift?
Faster flow (lower P) above and slower (higher P) below create upward lift.
Is this the same as solid pressure p = F/S?
No. Solid pressure uses p = F/S; here we use a qualitative flow–pressure idea (junior Bernoulli).
Does faster flow always mean lower pressure?
In the usual demos along a streamline, higher speed goes with lower pressure.
Is wing lift only from the upper surface?
Both surfaces matter via ΔP; the lab uses a simplified intuition model.