pascal's principle for pressure

7/28/2019 pascal's principle for pressure

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Pascal's Principle A pressure applied to a conf ined f lui d increases the pressurethr oughout by the same amount.

The Earth's atmosphere exerts a pressure on all objects with which it is in contact,

including other fluids.The pressure due to water pressure 100. m below the surface of a lake is

P = gh = 1.00 x 103

kg/m3

x 9.80 m s-2

x 100. m = 9.80 x 105

Pa = 9.7 atmP Total = P water + P air = 9.7 atm + 1.0 atm = 10.7 atm

The

brake

system

to the

left is apractica

l

applicat

ion of

Pascal's

Principl

e. F =

PASince

thepressure is the same at the Master Cylinder and the Brake Pads, a force applied to the

Master Cylinder gives a larger force at the Brake Pads. An important point, the distance

traveled by the pedal is greater than the distance traveled by the Brake Pads.

Thehydrau

lic lift

is

anothe

r

practic

al


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application of Pascal's Principle.P out = P in

F out F in-------- = -------

A out A in

F out A out

-------- = ----------

F in A in

F out / F in is the Mechanical Advantage of the system. If the area out is 20 times greater

than the area in, a 200. lbs force can lift a 4000. lbs car.Table of Contents

Problems1. The maximum gauge pressure in a hydraulic lift is 18 atm. What is the largest mass

vehicle it can lift if the diameter of the output line is 22 cm?
http://www.angelfire.com/nc3/pweb/lessons/pascalp.htm#Table%20of%20Contentshttp://www.angelfire.com/nc3/pweb/lessons/pascalp.htm#Table%20of%20Contentshttp://www.angelfire.com/nc3/pweb/lessons/pascalp.htm#Table%20of%20Contents


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2. Pascal placed a long tube with a radius of0.300 cm into a barrel with a 20.0 cm radius

top. When the water was filled to the 12.0 m

height the barrel burst.

(a) Calculate the mass of water in the tube.(b) Calculate the net force on the lid.

3. What is the total pressure on a diver 45.0 m below the sea? Physics Charts -Densities of Substances

4. The master cylinder of a brake system has a radius of 0.100 cm and the cylinders atthe brake pads have radii of 4.00 cm. If Debi can apply a force of 150. N on the brake

pedal, what is the force applied to slow down her car?Table of Contents

Answers1. The maximum gauge pressure in a hydraulic lift is 18 atm. What is the largest mass

vehicle it can lift if the diameter of the output line is 22 cm?
http://www.angelfire.com/nc3/pweb/charts/density.htmhttp://www.angelfire.com/nc3/pweb/charts/density.htmhttp://www.angelfire.com/nc3/pweb/charts/density.htmhttp://www.angelfire.com/nc3/pweb/lessons/pascalp.htm#Table%20of%20Contentshttp://www.angelfire.com/nc3/pweb/lessons/pascalp.htm#Table%20of%20Contentshttp://www.angelfire.com/nc3/pweb/lessons/pascalp.htm#Table%20of%20Contentshttp://www.angelfire.com/nc3/pweb/charts/density.htmhttp://www.angelfire.com/nc3/pweb/charts/density.htm


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1.013 x 10

5N m

-2

18 atm x -------------------------- = 1.82 x 106

N m-2

1 atm

22cm = 0.22 m = d

A = r2

= x ( 0.11 m )2

= 0.0380 m2

F = P x A = 1.82 x 106

N m-2

x 0.0380 m2

= 6.92 x 104

N

F 6.92 x 104

N

m = ---- = -------------------- = 7060 kg

g 9.80 m s-2

2. Pascal placed a long tube with a radius of0.300 cm into a barrel with a 20.0 cm radius

top. When the water was filled to the 12.0 m

height the barrel burst.

(a) Calculate the mass of water in the tube.(b) Calculate the net force on the lid.


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(a) m = V x D = r

2h x D = ( 0.00150 m )

2x 12.0 m x 1.00 x 10

3kg m

-3= 8.48 x

10-2

kg

(b)

F out A out F in x A out 8.48 x 10-2

kg x 9.80 m s-2

x x ( 0.200

m )2

-------- = ---------- => F out = ----------------- = ------------------------------------------------

----------------

F in A in A in ( 0.00150 m )2

F out = 1.48 x 104

N

3. What is the total pressure on a diver 45.0 m below the sea? Physics Charts - Densitiesof Substances

P total = P water + P atmosphere

P total = gh + P atmosphere = 1.025 x 103

kg m-3

x 9.80 m s-2

x 45.0 m + 101300 PaP total = 5.53 x 10

5Pa = 553 kPa

4. The master cylinder of a brake system has a radius of 0.100 cm and the cylinders atthe brake pads have radii of 4.00 cm. If Debi can apply a force of 150. N on the brakepedal, what is the force applied to slow down her car?

F out A out F in x A out 150. N x 4 x x ( 4.00 cm )2

-------- = ---------- => F out = ----------------- = ------------------------------------------- =

9.6 x 105

N

F in A in A in ( 0.100 cm )2
http://www.angelfire.com/nc3/pweb/charts/density.htmhttp://www.angelfire.com/nc3/pweb/charts/density.htmhttp://www.angelfire.com/nc3/pweb/charts/density.htmhttp://www.angelfire.com/nc3/pweb/charts/density.htmhttp://www.angelfire.com/nc3/pweb/charts/density.htm

pascal's principle for pressure

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