MAKE SURE YOU LEARN THE LABELS! THEY ARE FOR YOUR PROTECTION
Task 4 Task 4 Using your answers to Task 3, predict which paragraphs will have the
a What is the function of the calipers?
b Why do car wheels have vent holes?
c Where are the brakes mounted?
d What type of material are brake pads made from?
e What is the difference between the master and the wheel cylinder?
f What kind of energy does a moving vehicle have?
Task 5 Scan the text to check your predictions in Task 4, and find the answers to the questions.
D i i brakes
para
Disc brakes are used on cars and motorcycles. They work by I using friction and hydraulic power. The friction is generated when the brakes - stationary pads mounted to the suspension system - rub against metal discs turning with the wheels.
5 The pads are covered with a high-friction material. t h e resistance 2 of the pads against the rotating discs converts the energy of the
moving vehicle (kinetic energy) into heat energy in the brakes. As kinetic energy is lost, the car slows down.
This method of brakiRg produces a great deal of heat, so brakes 3
l o have to be made from a heat-resistant material, like asbestos. The
intense heat a h explains why car wheels need vent-holes around the centre: when the car is moving the slots ensure a flow of air over the brakes, helping to cool them down.
Whmthe driver presses the brake pedal, it pushes down the 4 15 piston in the master cylinder, so creating pressure in thewid. The
fluid is incorn~ressible. The pressure is transmittedto the wheel cylinder which forces the brake pads against the revolving disc. The mastercylinder hasa smaller diameter than the wheel cylinder.
Hence, a relatively small force applied on the pedal produces a zo large force on the brake pads.
The brake pads are held in a clamping device called a caliper.
The caliper system ensures that one brake pad is pushed against the inner surface of the disc while, simultaneously, the other pad is
pulled againstthe outer surface. This gives twice the braking
25 power. The action is like squeezing something between forefinger and thumb.
Source: Adapted from 'Inside out: Disc brakes', Education Guardian
Language study Verbs with up and down
In this book, you have studied a number of verbs followed by up or down. For example:
1 Transformers step up the voltage from 25 kV to 400 kVfor transmission.
2 Use as little force as possible to break down a machine into its components.
Task 6 Fill in the blanks in these sentences with either up or down. You have studied these verbs in similar contexts.
1 As the car slows ,kinetic energy is converted to heat.
2 An installation technician connects -cables and switchgear.
3 A plastic pellet in a washing machine door heats and pushes the lock into position.
4 Car wheels are ventilated to cool the brake discs.
5 Transformers are used on construction sites to step -- the mains voltage to avoid accidents with hand tools.
6 Students in David's maths class were split into three groups.
7 One of Lucy's friends came with the name Swingex-L.
8 Students should keep with subjects l i e maths and physics.
Word study Verbs + -en
Can you rewrite this sentence replacing the verb in italics with another verb or phrase of similar meaning?
The caliper system ensures that the disc is gripped on both sides.
Here is one way it can be done.
The caliper system makes sure that the disc is gripped on both sides
Verbs beginning or ending with en often have the meaning of becornelmake +
adjective.
Task 7 Replace the words in italics in the following sentences with a suitable en verb from this list.
ensure enlarge harden lengthen lessen lighten loosen roughen sharpen shorten soften strengthen tighten toughen weaken widen
1 Steel rods are used to make concrete beams stronger.
2 A torque wrench is used to make cylinder head bolts tight.
3 Thermoplastics can be made soft by heating them.
4 After thermosetting plastics become hard, they cannot be softened again.
5 A reamer is a tool used to make a hole larger.
6 Corrosion makes structures weak.
7 Compressive forces will make a beam shorter; tensile forces will make it longer.
8 Carbon fibre frames make racing bicycles lighter and stronger.
9 Oil can be used to make tight bolts loose.
10 Carbon steels are made tough by heating and quenching.
Writing Explaining an operation
Task 8
Task 9
Link the statements below to explain the operation of a hydraulic jack. Use the diagram to help you.
L I
Car body
Lever reservoir
Fig. 2
The jack is placed under the car.
The lever is moved up and down.
The movement is converted into a reciprocating motion.
The motion slides the piston back and forwards.
Each movement of the piston pumps a small amount of fluid.
The fluid is pumped from the reservoir through the one-way valve into the main cylinder.
This action gradually raises the jack.
The car is lifted from the ground.
The car is lowered.
This is done by releasing the one-way valve.
This allows the weight of the car to force fluid from the cylinder back into the reservoir.
The car slowly descends.
Divide your explanation into two paragraphs. Include a reference to Fig. 2.