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Idea:A car at a workshop can be raised up for service by pushing only one switch. This is one application of Pascal’s Principle in our daily life.

Activity 1: 2. Squeeze a toothpaste tube. How does the

pressure exerted by the thumb transfer to the mouth of the tube?

………………………………………………………………

3. When the piston is push, why does water spurt out in all direction with the same speed?

……………………………………………………………..

State Pascal’s Principle

Explain hydraulic systemA hydraulic system is a device in which a small applied force can give rise to a larger force.

A small input force, F1 is applied to the small piston, a ____________ is produced and will be _____________ throughout the liquid towards the big piston __________.

Based on the Pascal’s Principle, Pressure at small cylinder _____ Pressure at large cylinder

F1 = F2

A1 A2 Where: F1 = Input force F2 = Output force A1 = input piston area A2 = output piston area

Pressure multiply by surface area A2 will produce an output force F2.

F2 will lift up the load Hydraulic systems act as a _______

multiplier. They multiply the input force by a certain factor to gain a larger output force.

The magnitude of the force at the large piston depends on (a) the _________, applied to the small

piston,(b) the ratio of the ___________ area of the

piston,

When incompressible fluid is moved through a hydraulic system, the volume through which the input system moved must be the ________ as the volume through which the output system, Hence A1d1 = A2d2

A hydraulic system must not contain any _____ bubbles in any position of its hydraulic fluid system. This will reduce the _________ of the system as part of the applied force will be used up to compress the air bubbles.

Solve problem involving Pascal’s principle

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1.The figure shows a simple hydraulic system. Assume there is no friction in the system.

(a) what is the pressure at A?

(b) what is the pressure at B?

(c) what is the upward force produced?

(d) What is the effect on the hydraulic system if the cross-sectional area of the large piston is increase?

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1. A basic hydraulic system has small and large pistons with cross-sectional areas of 2 cm2 and 50 cm2 respectively. When a force of 20 N is applied to the small piston, it pushes down the piston by 20 cm.

Calculate (a) the pressure transmitted in the hydraulic

fluid,

(b) the force acting on the large piston,

(c) the distance moved by the large piston

(d) the magnification of the force.

Application of Pascal’s Principle

(1) Hidraulik Jack

When the handle is pulled, valve A is still closed and valve B opens so the ________ can be transmitted to the larger piston. The large piston will rise.

While the small piston is pulled out, valve B closes and valve A opens so the _____ in the tank enter into the hydraulic cylinder as a result of atmospheric pressure.

By moving the push-pull handle a number of times, the large piston can be raised carrying a heavy load.

The load is lowered without using the handle by opening the ___________ valve.

(2) Hydraulic Brake

(ii) Explain how does the brake system work?When the driver’s foot presses the brake pedal, the piston in the master cylinder exerts _____________ on the brake fluid. This pressure is ____________ to the wheel cylinder of all wheels.

On the figure above indicate the direction of motions of the front brake cylinder and the rear brake cylinder.

(iii) The pressure causes the pistons to press the brake shoes against the wheels. This produces _____________ force that cause the car to slow down or stop.

(iv) State the relationship between the liquid pressure in the front brake cylinder and the rear brake cylinder.

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(v) Explain why the piston of the wheel cylinder is larger than that of the master cylinder.

(vi) What is the function of the return spring?

___________________________________________

(vii) Why is the brake system in the car is less effective air bubbles are present in the brake fluid?

(viii) Why is the cross-sectional area of the rear brake cylinder of the right wheel is the same as the cross-sectional area of the rear brake cylinder of the left wheel?

3. A boy invented a machine to compress old newspaper. The machine consists of a hydraulic system with two pistons. Piston A has a smaller cross-sectional area compared to piston B.

(a) the function of this machine is based on a principle in physics. Name the principle,

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(b) Explain why a small force exerted by the boy can result in a much bigger force acting on the old newspaper

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4. Figure shows a hydraulic lift commonly used in a workshop. Highly compressed air is used to push the piston upwards. The force produces is enough to lift a car.

By referring to the diagram, explain how a car(a) can be lifted by the hydraulic lift.

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(b) Explain how the car can be lowered after rep air works are done

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5. Figure shows dentist treating a patient. The dentist presses on the input piston to raise the patient. The cross-sectional areas of the input piston and the output piston are 400 cm2

and 600 cm2 respectively.(a) Describe how the patient is raised to a

certain height.

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(b) How much force is exerted by the dentist in order to raise a patient of 54 kg?x/400 = 540/600x = 360 N

(c) If the patient is raised to a height of 8 cm, how far should input piston be pushed down?

Volume of water up = volume of water downX(400) = 600(8) x = 12 cm

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TUTORIAL 3.4

1. The figure shows a hydraulic pump.R

Which comparison is true?A. The force F is the same as the weight of

the loadB. The force F is greater than the weight of

the loadC. The pressure on piston P is the same

as the pressure on piston QD. The pressure on piston P is smaller

than the pressure on piston Q

2. A force of 20N is applied to the input piston in a hydraulic jack. If the input piston area and output piston area are 0.02 m2 and 0.1 m2 respectively, what is the output force?A 20 N B 50 NC 100 N D 200 NE 400 N

3. If the area of input piston and output piston are 0.03 m2 and 0.90 m2 respectively, what is the mass of object P.A 3.2 x 102 kg B 2.4 x 102 kgC 2.0 x 102 kg D 1.8x 102kgE 1.2x 102 kg

4. The figure shows a brake system of a car.

Which principle is used in this system?A Pascal’s principleB Bernoulli’s principleC Archimedes’ principleD Principle of conservation of momentum

5. Diagram below shows toothpaste being squeezed out from the tube.

Which principle explains the situation above? (2007)A. PascalB. BernoulliC. Archimedes

6. Diagram 8 shows a hydraulic brake system.

A driver steps on the brake pedal. Which relationship is correct?(2008)A. Pressure on P < Pressure on QB. Pressure on P = Pressure on QC. Pressure on P > Pressure on Q

7. Diagram 11 shows the shovel and the arm of a digger lifting a heavy load.

Diagram 11

Which principle is used in the arm of the digger? (2010)A. Pascal’s principleB. Bernoulli’s principleC. Principle of equilibrium of forcesD. Principle of conservation of momentum

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8. Diagram 12 shows a cross-sectional of a hydraulic jack. The weight of a car is 2.0 x 106 kg and the ration between the surface areas of the master piston to the slave piston is 1:15.

What is the force exerted on the master piston? (2012)

A. 1.3 x 106 NB. 1.3 x 107 NC. 3.0 x 106 ND. 3.0 x 107 N

9. SPM 2008 Question 7

Diagram 7.1 shows a hydraulic system. A force F is exerted on the small piston.

(a) (i) Name the principle involved in this hydraulic system.

Pascal’s Principle…………………………………

[1 mark]

(ii) Compare the pressure at point P and at point Q.equal…………………………………

[1 mark]

(b) Diagram 7.2 shows a hydraulic jack in a car service centre.

A force of 50 N is exerted on the small piston when the handle is pushed down. The cross-sectional areas of the small piston and the large piston are 0.04 m2 and 0.8 m2 respectively.

(i) Calculate the pressure exerted on the oil in the hydraulic jack.P = F/A = 50/0.04 = 1250 Pa

[2 marks]

(ii) Calculate the force that the oil exerts on the large piston.F = PA = 1250 x 0.8 = 1000 N

[1 mark]

(c) Based on Diagram 7.2, (i) explain how the handle is used to

lift the load to its maximum height.,push down the handle, valve B open, valve A closes. Pressure is transmitted and the oil enter the large piston. The large piston raise up.Pull up the handle, valve B closes, valve opens, oil from the reservoir enter the small piston. The process is repeated.

[2 marks]

(d) explain one modification to the large piston that enables the jack to lift a heavier load, [2 marks]

increase the surface area of large piston to produce large output force

……………………………………………

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(e) state how the load is lowered without using the handle.Opening the release valve.……………………………………………

[1 mark]

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