Measuring Pressure:More Practice

Measuring Pressure:More Practice

Measuring Pressure:More Practice

Measuring Pressure:More Practice

Measuring Pressure:More Practice

Measuring Pressure:More Practice

Pascal’s Principle: Student Success Criteria

I can state Pascal's principle, explain its applications in the transmission of forces in fluid systems, and conduct an laboratory investigation to demonstrate it.

SPH4C

CompressibilityRecall that liquids

are not very compressible: their volume remains more or less constant even if pressure is applied.

Pascal’s Principle Therefore, pressure applied to an

enclosed liquid is transmitted to every part of the liquid and to the walls of the container.

A hydraulic braking system transfers pressure from the brake lever through the system.

The hydraulic pressPascal used this principle

in the design of a device called the hydraulic press: a device in which a small force on a small piston is transmitted through an enclosed liquid and applies a large force on a large piston.

The hydraulic pressI.e., the pressure (pS) on the

small piston equals the pressure (pL) on the large piston:

L

L

s

s

Ls

A

F

A

F

pp

If A is increased, then F is also increased.

The hydraulic press: ExampleA force of 14 N is applied to a piston of area

0.01 m2, which is connected to another piston of area 0.25 m2. What is the force on the larger piston?

The hydraulic press: ExampleA force of 14 N is applied to a piston of area

0.01 m2, which is connected to another piston of area 0.25 m2. What is the force on the larger piston?

?

25.0

01.0

14

2

2

L

L

s

s

F

mA

mA

NF

The hydraulic press: ExampleA force of 14 N is applied to a piston of area

0.01 m2, which is connected to another piston of area 0.25 m2. What is the force on the larger piston?

?

25.0

01.0

14

2

2

L

L

s

s

F

mA

mA

NF

The hydraulic press: ExampleA force of 14 N is applied to a piston of area

0.01 m2, which is connected to another piston of area 0.25 m2. What is the force on the larger piston?

?

25.0

01.0

14

2

2

L

L

s

s

F

mA

mA

NF

N

m

mNF

A

AFF

A

F

A

F

L

s

LsL

L

L

s

s

35001.0

25.0142

2

Mechanical advantageThe Ideal Mechanical Advantage (IMA) of the system would be:

& Actual Mechanical Advantage (AMA) of the system would be

.

Mechanical advantageThe Ideal Mechanical Advantage (IMA) of the system would be:

& Actual Mechanical Advantage (AMA) of the system would be

.

s

L

A

AIMA

Mechanical advantageThe Ideal Mechanical Advantage (IMA) of the system would be:

& Actual Mechanical Advantage (AMA) of the system would be

.

s

L

A

AIMA

s

L

effort

load

F

F

F

FAMA

DistanceHowever, since the volume of the

larger cylinder is obviously larger, the distance the larger cylinder is displaced is smaller.

BrakesCar brakes incorporate both

levers and hydraulics:

the distance from the pedal to the pivot is four times the distance from the cylinder to the pivot, so the force at the pedal will be increased by a factor of four before it is transmitted to the cylinder. (2nd class lever).

BrakesThe diameter of the brake

cylinder is three times the diameter of the pedal cylinder, increasing the area and therefore the force by a factor of nine.

All together, this system increases the force of your foot by a factor of 36

(4 x 9 = 36).

BrakesSo if you put 100 N of force on the pedal, 3600

N will be generated at the wheel squeezing the brake pads

More PracticePascal’s Principle Lab Activity