Notes: ρfresh water = 1,000kg/m3 g = 10N/kg 1,000mbar = 1 bar = 100,000Pa
Q5) ∆p = h × ρ × g 250000- 100000 = h x 1000 150000 = h x 1000 x 10 150000/ 1000 = 15m Q6) ∆p = h × ρ × g ∆p = 50 x 420 (0.42x 1000 to change it into kg/m3) x 1.4 ∆p = 294000Pa 1,000mbar = 1 bar = 100,000Pa so 1,600mbar = 1.6 bar = 160,000Pa 29,400+160,000 = 189,400Pa TOTAL PRESSURE = 189,400Pa or 189.4 kPa
5.6 Plenary
· Which diver experiences the greatest pressure?
∆p = h × ρ × g They both experience the same amount of pressure because the height is the same and we assume that the density and the gravitational field strength will be the same in the 2 places. so therefore the pressure must be the same.
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 [cid:image001.jpg@01CC94C6.C4A53AA0] · 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 [cid:image002.jpg@01CC94C6.C4A53AA0] Notes: ρfresh water = 1,000kg/m3 g = 10N/kg 1,000mbar = 1 bar = 100,000Pa Q5) ∆p = h × ρ × g 250000- 100000 = h x 1000 150000 = h x 1000 x 10 150000/ 1000 = 15m Q6) ∆p = h × ρ × g ∆p = 50 x 420 (0.42x 1000 to change it into kg/m3) x 1.4 ∆p = 294000Pa 1,000mbar = 1 bar = 100,000Pa so 1,600mbar = 1.6 bar = 160,000Pa 29,400+160,000 = 189,400Pa TOTAL PRESSURE = 189,400Pa or 189.4 kPa 5.6 Plenary 12 October 2011 07:23 · Which diver experiences the greatest pressure? [cid:image003.jpg@01CC94C6.C4A53AA0] ∆p = h × ρ × g They both experience the same amount of pressure because the height is the same and we assume that the density and the gravitational field strength will be the same in the 2 places.
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 [cid:image001.jpg@01CC94C6.05BEAF40] · 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! http://www.youtube.com/watch?v=7bJkaFByiA0&feature=related 5.5 Demo 2 - Collapsing Bottle 12 October 2011 07:19 · Collapsing Bottle [cid:image002.jpg@01CC94C6.05BEAF40]
5.4 Starter 07 October 2011 11:46 [cid:image001.png@01CC94B8.E00F63A0] [cid:image002.png@01CC94B8.E00F63A0] 5.4 Starter 2 explained 07 October 2011 09:04 > · Your finger pushes on the pin and the pin pushes back on your finger · N3L tells us that all these two forces are equal in size · The pin pushes on the wall and the wall pushes back on the pin · N3L tells us that all these two forces are also equal in size · If the surface area is large then the force is spread over a large area and the pressure is low · If the surface area is small then the force is spread over a small area and the pressure is high · You would like the pressure on your finger to be low and the pressure on the wall to be high · The other way round is painful! 5.4 07 October 2011 10:37 · 5.4 recall and use the relationship between pressure, force and area: pressure = force / area p = F / A [cid:image004.png@01CC94B8.E00F63A0] 5.4 Pressure Questions 07 October 2011 11:47 · PFY p.91, Q.3 and 7. [cid:image005.png@01CC94B8.E00F63A0] 3) p=F/A 100,000N=F/10 100,000 x 10 = 1,000,000 N [cid:image006.png@01CC94B8.E00F63A0] [cid:image008.jpg@01CC94BE.1EB1D610] 7a) p=F/A p= 500/5 P= 100N/ cm2 b) p= F/A 100= F/20 P= 2000N [cid:image009.png@01CC94B8.E00F63A0] Question 1) Inuits wear snow shoes because if you look at the relationship between p=F/A when the area decreases the pressure increases. for example- 12/6 (area) = 2 (pressure) but 12/3 (area) =4 (pressure) So if there is a large surface area on the snow shoes the Inuits will not sink into the snow. Question 2) Tractors have big tires because p= F/A. when the area increases the pressure decreases. If the tractors have small tires the pressure will increase and the tractor will sink into the ground.
Instructions for Objective 5.4 1. 5.4 Starter. Who’s telling the truth? Read the explanation underneath. 2. 5.4 Starter 2. Open the attached animation. Why does pushing a drawing pin into the wall not hurt your finger? (as long as you get the pin the right way round!) Read the explanation below. 3. 5.4. Watch the video clips. Learn the formula and units 4. 5.4 Pressure Question. Forward this e-mail to your blog. Type your answers under the questions. 5. 5.4 Written Questions. Type your answers under the questions. 6. Answers to steps 4 and 5 will be sent separately. Don’t look at them until you’ve done the work! Best wishes, Mr B 5.4 Starter 07 October 2011 11:46 [cid:image001.png@01CC94B8.E00F63A0] [cid:image002.png@01CC94B8.E00F63A0] 5.4 Starter 2 explained 07 October 2011 09:04 > · Your finger pushes on the pin and the pin pushes back on your finger · N3L tells us that all these two forces are equal in size · The pin pushes on the wall and the wall pushes back on the pin · N3L tells us that all these two forces are also equal in size · If the surface area is large then the force is spread over a large area and the pressure is low · If the surface area is small then the force is spread over a small area and the pressure is high · You would like the pressure on your finger to be low and the pressure on the wall to be high · The other way round is painful! 5.4 07 October 2011 10:37 · 5.4 recall and use the relationship between pressure, force and area: pressure = force / area p = F / A [cid:image004.png@01CC94B8.E00F63A0] 5.4 Pressure Questions 07 October 2011 11:47 · PFY p.91, Q.3 and 7. [cid:image005.png@01CC94B8.E00F63A0] 3) p=F/A 100,000N=F/10 100,000 x 10 = 1,000,000 N [cid:image006.png@01CC94B8.E00F63A0] [cid:image008.jpg@01CC94BE.1EB1D610] 7a) p=F/A p= 500/5 P= 100N/ cm2 b) p= F/A 100= F/20 P= 2000N [cid:image009.png@01CC94B8.E00F63A0] Question 1) Inuits wear snow shoes because if you look at the relationship between p=F/A when the area decreases the pressure increases. for example- 12/6 (area) = 2 (pressure) but 12/3 (area) =4 (pressure) So if there is a large surface area on the snow shoes the Inuits will not sink into the snow. Question 2) Tractors have big tires because p= F/A. when the area increases the pressure decreases. If the tractors have small tires the pressure will increase and the tractor will sink into the ground.
