chap13 pps Automotive technology at University of Cambridge

Torque is the term used to describe rotating force that may or may not result in motion, measured as force multiplied by the length of the lever through which it acts.. 1 pound­foot =

start

• Explain kinetic energy and why it is so

important to brake design.

• Discuss mechanical advantage and how it is

used in a vehicle.

• Explain the coefficient of friction.

• Describe the difference between heat and

acid material • alkaline • brake • brake horsepower (bhp) • BTU (British Thermal Unit)

caustic material • Celsius (centigrade) • conduction •

conductor • convection • dynamometer (dyno or dyn)

energy • Fahrenheit • first-class lever • force • fulcrum

horsepower • hypothesis • inertia • insulator

kinetic energy • leverage • mass • mechanical advantage Newton’s laws of motion

KEY TERMS:

pedal ratio • pH • potential energy • power • propagation

radiation • root cause

scientific method • second-class lever

third-class lever • torque

weight • work • wrought alloys

KEY TERMS:

SCIENTIFIC METHOD

The  scientific method is a series of steps taken to solve a problem. It 

help eliminate errors and achieve an accurate result. A scientific method  involves:

perform research, a scientific approach to problem solving is very important

Applying the five whys:

First why—What caused the battery to become discharged? To answer this question requires observation and creating of a 

Third why—The charging system was not working correctly. A visual inspection found that the generator (alternator) drive belt 

Torque is the term used to describe rotating force that may or may 

not result in motion, measured as  force multiplied by the length of 

the lever through which it acts. If a one­foot­long wrench is used to  apply 10 pounds of force to turn a bolt, then you are exerting 10 

pound­feet of torque. 

The metric unit for torque is Newton­meters

1 pound­foot = 1.3558 Newton­meters

1 Newton­meter = 0.7376 pound­foot

Figure 13–2 Torque is a twisting force

equal to the distance from the pivot

point times the force applied

expressed in units called pound-feet

See a conversion chart on Page 97 of your textbook

Work is accomplishing movement when force (torque) is applied. 

It is calculated by multiplying the applied force by the distance the object moves

If you applied 100 pounds of force to move an object 10 feet, then you accomplished 1,000 foot­pounds of work

Figure 13–3 Work is calculated by multiplying force times distance If you push 100 pounds 10 feet, you have done 1,000 foot-pounds of work.

The designations for torque and work are often confusing Torque is expressed in pound-feet because it represents a force exerted a certain distance from the object and acts as a lever Work, however, is expressed

in foot-pounds because work is the movement over a certain distance (feet) multiplied by the force applied (pounds) Engines produce torque and service technicians exert torque represented by the unit pound-feet.

The designations for torque and work are often confusing Torque is expressed in pound-feet because it represents a force exerted a certain distance from the object and acts as a lever Work, however, is expressed

in foot-pounds because work is the movement over a certain distance (feet) multiplied by the force applied (pounds) Engines produce torque and service technicians exert torque represented by the unit pound-feet.

What is the Difference Between Torque and Work?

POWER AND HORSEPOWER

Power means the rate of doing work, and equals work divided by 

time. If the object is moved in 10 seconds or 10 minutes does not 

make a difference in the amount of work accomplished, but it does  affect the amount of power needed. Power is expressed in units of 

NEWTON’S LAWS OF MOTION

although this part is designed not to move

square of any increase in vehicle speed.

Mass is the amount of matter in an object One of the properties of mass is

inertia Inertia is the resistance to being put in motion and the tendency to remain in motion once it is set in motion

The weight of an object is the force of gravity on the object and may be

defined as the mass times the acceleration of gravity.

Therefore, mass means the property of an object and weight is a force.

Mass is the amount of matter in an object One of the properties of mass is

inertia Inertia is the resistance to being put in motion and the tendency to remain in motion once it is set in motion

The weight of an object is the force of gravity on the object and may be

defined as the mass times the acceleration of gravity.

Therefore, mass means the property of an object and weight is a force.

What is the Difference Between Mass and Weight?

No vehicle can stop on a dime The energy required to slow or stop a

vehicle must be absorbed by the braking system All drivers should be

aware of this fact and drive at a reasonable speed for the road and traffic conditions.

No vehicle can stop on a dime The energy required to slow or stop a

vehicle must be absorbed by the braking system All drivers should be

aware of this fact and drive at a reasonable speed for the road and traffic conditions.

Brakes Cannot Overcome the Laws of Physics

Figure 13–7 A first-class lever increases

force and changes the direction of the

force.

Figure 13–8 A second-class lever

increases force in the same direction

as it is applied.

Figure 13–9 A third-class lever reduces

force but increases the speed and travel

of the work.

HEAT AND TEMPERATURE

Heat and temperature are related but not the same. Temperature is the intensity of the heat source, heat is the quantity of heat. 

removed (air conditioner) from a space

If a material is a good conductor of heat, it is also a good conductor of

electricity Most conductors are metals, such as steel, copper, aluminum, and brass Most insulators are nonmetals, such as plastic and rubber

Therefore, if a material does not conduct heat, it usually will not conduct

electricity.

If a material is a good conductor of heat, it is also a good conductor of

electricity Most conductors are metals, such as steel, copper, aluminum, and brass Most insulators are nonmetals, such as plastic and rubber

Therefore, if a material does not conduct heat, it usually will not conduct

electricity.

Conductors and Insulator

A coat is worn in cold weather to keep warm Does it keep the cold out or the heat in? Actually, both, but because heat travels from a warm object (human body) to a colder object (outside cold air), the primary purpose of a coat is to keep the body heat from escaping into the cold air.

How Does a Coat Keep You Warm?

absorb heat from another body. Heat always flows from a warmer object to a colder object

Thermodynamics is the study of the relationship among temperature,

pressure, and volume changes The laws of thermodynamics help

engineers design and develop engines with higher efficiency

Thermodynamics is therefore used in the design of the cooling system, as well as in the engine, because the more heat created by the burning of fuel

in the engine, the more power the engine can develop using the same or less amount of fuel.

Thermodynamics is the study of the relationship among temperature,

pressure, and volume changes The laws of thermodynamics help

engineers design and develop engines with higher efficiency

Thermodynamics is therefore used in the design of the cooling system, as well as in the engine, because the more heat created by the burning of fuel

in the engine, the more power the engine can develop using the same or less amount of fuel.

What is Thermodynamics?

ACIDS AND BASES

indicate the amount of chemical activity. The term pH is from the  French word pouvoir hydrogine, meaning “hydrogen power.” 

battery (an acid surface)

Acids have a very strong affinity for water and as a result, if water is

poured into acid, the resulting reaction would be extremely violent and acid would be forced outward in all directions Always pour acid into water,

never water into acid Technicians seldom need to work with acids

because even battery electrolytes from the water and acid are premixed to help prevent the possibility of a technician creating a harmful reaction.

Acids have a very strong affinity for water and as a result, if water is

poured into acid, the resulting reaction would be extremely violent and acid would be forced outward in all directions Always pour acid into water,

never water into acid Technicians seldom need to work with acids

because even battery electrolytes from the water and acid are premixed to help prevent the possibility of a technician creating a harmful reaction.

Can Water and Acid be Mixed Together?

volume of the gas inside is reduced but the pressure is increased

Charles’s Law  1787 by French scientist, Jacque Charles (1746–

1823). States that as the temperature of a gas increases, the 

SOUND AND ACCOUSTICS

20,000 Hertz cannot be detected by humans

Intensity  Intensity of sound, called loudness, is measured in 

decibels (dB), named for Alexander Graham Bell (1847–1922), 

inventor of the telephone

According to acoustic engineers, about 80% of  noise created by 

the movement of the tires on the road is transmitted through the 

According to audiologists (hearing and speech doctors), a person should wear ear protection if the level of sound requires that your voice be raised

in order to be heard Any level that exceeds 90 dB requires the use of ear protection to avoid hearing loss This means that ear protection should be worn when using a power mower or using an air tool, such as an air impact wrench or air ratchet.

According to audiologists (hearing and speech doctors), a person should

wear ear protection if the level of sound requires that your voice be raised

in order to be heard Any level that exceeds 90 dB requires the use of ear protection to avoid hearing loss This means that ear protection should be worn when using a power mower or using an air tool, such as an air impact wrench or air ratchet.

Wear Hearing Protection

Bakelite (phenol formaldehyde resin)

Polyester resin

Epoxy resin

such as PP or PE. If no marking is visible, it is still possible to 

identify the type of plastic using a simple basic test

Often replacement plastic parts are available in only one color and must be painted to match the original. A burn test is used to test if the plastic part

wire test is performed. Heat a copper wire and touch the heated 

wire to a hidden surface of the part. After melting some plastic 

onto the wire, return the wire to the flame and observe the color of the flame. If the color is green/blue or turquoise, then the plastic is polyvinyl chloride (vinyl)

IRON AND STEEL

the alloy giving the metal a gray color. Gray cast iron is used for 

engine blocks

NOTE: Cast iron contains graphite, which acts as a lubricant when being  machined. As a result, cooling oil or water is not needed when making cast  iron brake rotors or brake drums.

machined. As a result, cooling oil or water is not needed when making cast  iron brake rotors or brake drums.

SAE STEEL DESIGNATIONS

forgings and machined components

High carbon steel  usually between 60 and 100 parts (0.60 and 1.00%) carbon and is very strong. Commonly used in vehicle 

ALUMINUM AND ALUMINUM ALLOYS

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