5.5 & 5.6

5.5

07 October 2011

10:40

·         

5.5 understand that the pressure at a point in a gas or liquid which is at rest acts equally in all directions

5.5 Demo 1 - Magdeburg Hemispheres

12 October 2011

07:19

·         Magdeburg Hemispheres

 

·         The original experiment was done by using two teams of wild horses to try and pull the hemispheres apart

·         And here are the horses I was talking about!

5.5 Demo 2 - Collapsing Bottle

12 October 2011

07:19

·         Collapsing Bottle

 

5.6

07 October 2011

10:40

·         

5.6 recall and use the relationship for pressure difference:

 

        pressure difference = height × density × g

                               ∆p = h × ρ × g

 

 

∆p = pressure of the fluid (N/m² or Pa)

h = height of the fluid (m)

ρ = density of the fluid (kg/m³)

g = gravitational field strength (N/kg)

5.6 Demo - squirting water column

12 October 2011

07:24

·         The bottom hole squirts water the furthest

·         Because the water at the bottom has the greatest pressure

·         Because in the formula ∆p = h × ρ × g, ρ is constant, g is constant and h is large

·         So ∆p = large

5.6 Questions

07 October 2011

11:53

Collins, p.107

Q5) 

 

5.             p=hxpxg

150000 = hx1000x10

h=15m

 

6.             ρ = 0.42g/cm³ = 420kg/m³

 P=hxpxg

P =50x420x1.4

P =29,400Pa

 1,000mbar = 1 bar = 100,000Pa

1.6 bar = 160,000Pa

 

So total pressure = 29,000+160,000 = 189,000Pa 

Notes:

ρ_{fresh water} = 1,000kg/m³

g = 10N/kg

1,000mbar = 1 bar = 100,000Pa

5.6 Plenary

12 October 2011

07:23

·         

Which diver experiences the greatest pressure?

 

They both experience the same pressure, because they are down at the same depth.