Date post: | 14-Jun-2015 |
Category: |
Education |
Upload: | keith-warne |
View: | 7,719 times |
Download: | 1 times |
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Pressure
K Warne
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
?? Questions ??Why?• Do drawing pins work?
• is it easier to walk through deep snow using snowshoes –or ski’s?
• Is it easier to cut with a sharp knife?
• Dangerous to put aerosol cans into a fire?
• Does it hurt your ears when you swim deep underwater?
• Could you get sucked out of a airliners window if it breaks?
Answer: PRESSURE!
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
PressurePressure is a measure of the force exerted per unit area.
ForcePressure =
area
Units: force - newtons (N)
area - meters squared (m2)
Pressure: N/m2 = pascal (Pa)
Calculate the pressure exerted by a 50N force
on a 0.1m2 area.
Pressure = force/area
= 50/0.1
= 500 Pa (N per m2)
F
P xA
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
?? Answers??Why?• Do drawing pins work?
• is it easier to walk through deep snow using snowshoes – or ski’s?
• Is it easier to cut with a sharp knife?
• Dangerous to put aerosol cans into a fire?
• Does it hurt your ears when you swim deep underwater?
• Could you get sucked out of a airliners window if it breaks?
BECAUSE• Small area of point creates HIGH PRESSURE – large surface on
thumb low pressure
• Large surface area reduces pressure – feet do not penetrate snow! You walk on top!
• Small surface of sharp edge creates HIGH PRESSURE.
• Cans pressurized gas – pressure increases with temp – explode!
• Pressure increases with depth.
• High pressure inside – low pressure outside – gas flows from HIGH to LOW PRESSURE.
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
• To calculate your area - convert to m2.
Estimated area lying
down.
194x75=14550cm2
14550/10000 = 1.455m2
Body
Pressure = force/area
= your mass x 10
area of your body
= 60x10/1.455
= 412 Pa
194cm
75cm
100 cm = 1m
(100)2 cm2 = 1m2
10 000cm2 = 1m2
Pressure exerted by your body
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Pressure of an object
Pressure = force/area
=(weight)/(l x w)
=
2.5kg
Rectangle/Square
W = 20cm
L = 60cm
Calculate the pressure exerted on the ground by each of these objects.
(Length measurements must be in meters.)
Circular Based
100gr
r = 30cm
Pressure = force/area
=(weight)/(∏x r 2)
=
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Pressure of an object
Pressure = force/area base
The area of the base in contact with the ground must be used to calculate the pressure.
Rotate each of the bricks (B & C) to show how they need to be placed so as to exert the MOST (B) and LEAST (C) pressure.
A
B
C
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
An elephants Pressure
Calculate the pressure
exerted by an elephant
which has a mass of 2.3
tonnes (1tonne = 1000kg)
and a foot diameter of 50
cm.
Force =
Area =
Pressure =
From World Book © 2002 World Book, Inc., 233 N.
Michigan Avenue, Suite 2000, Chicago, IL 60601. All
rights reserved. © Peter Davey, Bruce Coleman, Inc.
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Stillettos
• Calculate the pressure
exerted by a 50 kg lady
wearing stiletto heels
having an area of 1cm2 .
Force =massx10
=
Area =
Pressure = force/area
=Pa
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Liquid pressure• Observation: Water squirts our equally far in all
directions at the same depth.
Liquids cannot be compressed! Because of this fact;
• Pressure is the same at all points at the same depth
• Pressure is exerted EQUALLY in all directions.
B C
PA = PB = PC
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Liquid Pressure
The pressure increases
with depth.
PA …. PB ….PC
A
B
C
Calculate how much the
pressure increases for every
metre of depth in water. (use
g = 10 N.kg-1)
p =
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Liquid pressure• Pressure is the same at all points at the same depth
• Water squirts our equally far at the same height!
A B C
PA = PB = PC
The hydrostatic pressure at any given depth is found by
p = x g x h= density of liquid (1g/cm3
or 1000 kg/m3 water)
g = gravitational
acceleration (10 m/s2)
h = height of column of
water (depth)
Show that p =
hg and that the
units are still
N/m2 (Pa)
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Liquid pressure• Pressure is the same at all points at the same depth
A B C
PA = PB = PC
The pressure at any given depth is
found by
p = F /A
= weight /A
= mxg /A
= xv xg /A
= x(Axh)xg /A
p = x h x g
p = F /A
F = weight
Weight = m x g
m = density () x volume
Volume = area x h
Show that p = hg and that the units are still N/m2 (Pa)
Units (Kg/m3) h(m) g(N/Kg) = (Kg/m3).(m).(N/Kg) = N/m2
HYDROSTATIC
PRESSURE DENSITY OF
THE LIQUIDDEPTH AT
WHICH P
MEASURED
GRAVITATIONAL
ACCELERATION
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Liquid Pressure
A B
Only the depth affects pressure.
The pressure at A and B would be equal!
Calculate the pressure at the
bottom of each of these containers
if the liquid has a density of 1500
kg/m3. The diameter of A is 5m
and B is 50cm and both are 2.75m
deep.
p = hg = (1500)(2.75)(10) = 4 125 Pa
2.75m
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Liquid PressureThe TOTAL pressure at any point in a liquid includes the
atmospheric pressure exerted on the liquid surface!
p = atmos + hg = ……………………= …………………. Pa
2.5m
Atmospheric pressure 100 000 Pa
Hydrostatic pressure = hg
Hydraulic
Calculations
…………..force
……………..
FORCE!
……….
distance
………
distance
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY
For FULL presentation click HERE >>www.warnescience.net
Hydraulic Pressure
• Pressure applied to the liquid is exerted ……………… throughout the liquid ( ).
Force = ………….. x ……….
• The large piston has a
greater area so experiences a greater ……....
• The smaller piston however moves a greater …………. to displace the same ……….
Hydraulic Press
Liquid (hydraulic fluid) -
cannot be compressed.
ForceFORCE!
Hydraulic Calculations
A builds a hydraulic lift to lift 1250N on a surface area of
12m2, if he exerts a force on the liquid over an area of
0.5m2, what is the magnitude of the force he exerts.
F1
A1
F2
A2
=
F2
……=
F2
……=
F2 =
P1 = p2Summary:
1. F1 =1250N,
A1 = 12m2
2. F2 = ?
A2 = 0.5m2
…….
…..
…….
……..
………………… = …………….
Hi -
This is a SAMPLE presentation only.
My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as
other resources, are freely available on my resource sharing website:
www.warnescience.net
(paste into your browser if link above does not work)
Have a look and enjoy!
Keith Warne