天文学课件7

Any other examples?
Pascal’s Principle F1/S1=F2/S2
Surface Tension
Water on glycerin (甘油) Δt=5s
Surface Tension
F l F l
γ is the surface force per unit length.
ExplosivelyFormed Projectile (EFP)
Knowledge is the power!
zhj_fox@zju.edu.cn
If A1 > A2 , then v1 < v2 . Who is acting the force?
1. Static pressure (v1= v2=0)
p2- p1=- ρg(y2-y1)
2. Dynamic pressure (if y1=y2)
1 2 1 2 v1 p1 v 2 p 2 2 2
Blaise Pascal (1623—1662)
P gh
Atmospheric Pressure
Question: the weight of atmosphere?
ห้องสมุดไป่ตู้
Water tower
How?
Intravenous Drip
Siphon phenomenon (虹吸现象)
P=F/S
High-pressure water jet cutting
Shaped Charge (聚能装药)
Anti-tank missile VS tank
Explosive Reactive Armor
Easy bomb IED (Improvised Explosive Devices)
ExplosivelyFormed Projectile (EFP)
Thrust on a rocket
A Long March II F rocket blasts off with the Shenzhou VII in the rocket base of Jiuquan in Northwest China's Gansu Province on Sept. 25, 2008.
3. Compressible, viscous flow
can you explain these phenomena ?
Keep away from the train!
XB-70 Valkyrie Bomber
Sidespin
Dynamic lift
1 2 v p gy cons tan t 2
Capillary Phenomena (毛细现象)
水
水銀
Tell me why
perpetual motion machine (永动机)
Why?
Superfluidity (超流 )
Bernoulli effect
Daniel Bernoulli
(1700-1782)
vA const , Steady vA R const , incompress ible
The aircrafts’ wings
Takeoff
Flap (襟翼)
Landing
Engine first!
Fly with ONE wing!
Parachutes
How about large passenger aircraft ?
Boeing 737
3 tons 1200 m2
About 50 tons
Wind Tunnel (风洞)
“Wind Tunnel”
Vehicle’s Wings
Why they need wings?
Do they need the wings?
Boomerang (飞去来器)
How does it work?
Turbulence (紊流)
Boat, ship and submarine
Question: a). submarinr water b). submarinr water c). submarinr water
Freshwater and Seawater
The Dead Sea
Question: What will happen if a boat or ship sailed from freshwater to seawater?
Fluid
Solid Liquid Gas
Condensed Matter Fluid
Variation of Pressure in a Fluid at Rest
Buoyancy
Zeppelin Rigid airship (齐柏林飞艇)
Fire Balloon (热气球)
Sulfur hexafluoride (SF6)
Fish
Question: Some fish move extremely slowly,
and it’s hard to tell whether they even alive. However, if a fish is floating at a middle height in your aquarium（鱼缸） and not at the top or bottom of the water, you can be pretty certain that it’s alive. Why?
Question: Will bubbles change their size as the
depth changes?
Archimedes: gold crown?
曹冲称象
Question: Do you have any other way?
Center of buoyancy
Pressure
This is Bernoulli’s equation.
Why?
Aircraft
Why they can fly?
Wing
Kite
Why kite can fly?
Hydrofoil craft (水翼艇 )
Frisbee
How does it work?
Tell me the shape of aircrafts’ wings