Resources

WORK

Work is the energy transferred to or from an object as the result of the action of a force.

Positive work is a transfer of energy to the object, and negative work is a transfer of energy from the object.

Work = Force x Displacement

The unit of work is the joule*, J, which is defined as the amount of work done when a force of 1 newton acts for a distance of 1 m in the direction of the force. Thus, 1 J = 1 N m

NOTE: If the body moves in the same direction as the force the angle is 0 degree, then;

                    Workdone = F x d

Where d is the distance.

When the angle is 90 then the work done is zero.

FORCE – DISTANCE GRAPH

If a graph is plotted of experimental values of force(on the y-axis) against distance moved (on the x-axis), the graph is called force-distance graph or work diagram.

The area under the graph represents the work done.

A constant force F, used to raised  a load of distance d, can be represented by a force – distance graph shown below;

constant
Force-distance graph 

Similarly, a spring extended by distance, d by a force F, can be represented by a force – distance graph as shown below;

string
force-distance graph
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Dimensions 1

Any physical quantity can be characterized by dimensions. The magnitudes assigned to the dimensions are called units.

The system of units used in Engineering is the Systeme International d’Unites also known as International System of Units and is based on the metric system.

A unit has to have a special name and symbol. The usefulness of a unit is  as a means of communicating to everyone who does science how it was particularly defined.

Are classified into two types:

  • Basic Units
  • Derived Units

BASIC UNITS:  Basic units are those units from which other units are derived. Some basic dimensions such as mass m, length L, time t, and temperature T are referred to as Basic dimensions.. Basic units are also known as primary or fundalmental units.

NOTE: Length, Mass, Time are basic quantities, while their units(meter, kilogram, seconds) are basic units.

 

 

PLANE STRESS AND STRAIN(2)

DIRECT STRESS

The Force transmitted across any section, divided by the area of that section, is called intensity of stress or stress. Forces acting on a material cause a change in dimensions and the material is said to be in a state of stress.

DIRECT STRESS

Stresses which are normal to the plane on which they act are called direct stresses and  either tensile or compressive

stress for

The symbol  σ is called SIGMA

DIRECT STRAIN

Strain is a measure of the measure of the deformation produced in the member by the load. The fractional change in a dimension of a material produced by a force is called the strain. For a tensile or compressive force, the strain is the ratio of the change of length to the original length. The symbol used for the strain is ε (Greek epsilon).  Tensile strain will be positive While compressive strain will be negative.

NOTE: Strain is dimensionless and is often expressed as a percentage

strain for

 

Humidity Control(2)

HUMIDIFIERS

A humidifier is a device that increases humidity (moisture) in a single room or an entire building.  A humidifier works by adding water vapor to the indoor air. Humidifiers accomplish this by one of the following four methods or variations/combinations of producing vapor from the water.

NOTE: Humidifiers can also be attached to the ductwork.

TYPES OF HUMIDIFIERS

Some types of humidifiers are:

1.Central Humidifiers;

2.Portable Humidifiers.

CENTRAL HUMIDIFIERS:

These types o humidifiers are attached to the ductwork and add moisture to the airspace before it leaves the supply grill to the space to be conditioned.

They can be installed ;

1.Via bypass ductwork

2.Directly into the return or supply ductwork

Some types of central humidifiers are;

BYPASS HUMIDIFIER: Just as the name suggests, it is used to bypass air flowing from the supply air plenum. Not all the conditioned air follows this bypass route. The air that is bypass is humidified.

Picture1

EVAPORATIVE HUMIDIFIERS: This type of humidifier add moisture to the air through evaporation. It contains an element that is kept damp.

Some of the moisture in the element  evaporates as air is forced through the humidifiers thereby increasing the humidity of the air.

The types of evaporative humidifiers are;

Plate humidifiers

Fixed filter humidifiers

Rotating drum humidifiers(Used for restricted spaces)

Rotating disk humidifiers

PORTABLE HUMIDIFIERS

Portable humidifiers are standalone units that are placed in the spaces where the humidity level is to be maintained. They are used for room control humidity and not building humidity control.

Many portable humidifiers add moisture by circulating air across a wet filter, though some units ultrasonic humidification.

Portable Humidifiers

Portable humidifiers are easy to maintain. The water tank and the wet filter can be removed and cleaning or replaced depending on the conditioned.

It uses a float-operated switch that turns on an indicator light when the water level in the water pan gets too low. Most of the units must be refilled manually.

Humidity Control (1)

Humidity is concerned with the physical properties of mixtures of air and water vapor. humidity, which is the amount of water vapor in the air, can make hot temperatures even more unbearable than they already are.

Humidity is an important factor to understand because it affects both weather and climate as well as global climate change. Humidity also affects indoor environments, so understanding it can help you determine the best place to store your books, clothing and other important items in your house.

WHY CONTROL HUMIDITY? 

  • Comfort: This is why air conditioners were introduced in the first place.
  • Storage and Preservation.
  • To prevent corrosion.
  • Mildew and Mould prevention.
  • To prevent condensation

Humidistat:

A humidistat is a control device that responds to changes in humidity and activates and deactivates parts of the humidity control systems.

These humidity control systems include:

1.Humidifiers

2.Dehumidifiers

3.Air mixers

NOTE: Humidistats are available with analog dial adjustments or incremental digital adjustments for controlling relative humidity

Trading Bloc

A trade bloc is a type of intergovernmental agreement, often part of a regional intergovernmental organization, where barriers to trade (tariffs and others) are reduced or eliminated among the participating states. It is a group of countries within a geographical region that protect themselves from imports from non-members. A group of countries who have joined together to promote trade. This might be through relaxing protectionist barriers or even having a common currency.

Examples of trading blocs include :

EU-European Union), NAFTA -North American Free Trade Agreement), ASEAN-Association of Southeast Asian Nations, EEA – The European Economic Area, CEFTA -The Central European Free Trade Agreement.

Types of trade Bloc

Preferential Trade Area: Preferential Trade Areas (PTAs) exist when countries within a geographical region agree to reduce or eliminate tariff barriers on selected goods imported from other members of the area. This is often the first small step towards the creation of a trading bloc.

Free Trade Area: Free Trade Areas (FTAs) are created when two or more countries in a region agree to reduce or eliminate barriers to trade on all goods coming from other members.

Customs Union: Countries that belong to customs unions agree to reduce or abolish trade barriers between themselves and agree to establish common tariffs and quotas with respect to outsiders.

Common Market: This is a customs union in which the members also agree to reduce restrictions on the movement of factors of production – such as people and finance – as well as reducing barriers on the sale of goods

Advantages of Trade Bloc
• Firms can enjoy economies of scale, in a trading bloc, firms can produce goods and services with a lower average cost because trading blocs allows firm to have large scale of production
• Trading blocs brings firms closer to each other and create greater competition, consumers will be benefited with better quality of goods and services in a lower price, they will have more choices
• Firms within the bloc can enjoy a tariff free environment
• Countries within the trading bloc can have more international bargaining power

Disadvantages of Trade Bloc
• unfair against countries out of the Trading Blocs –
• Groups not within the Blocs have to pay Tariffs in order to transfer goods
• Countries within the Blocs have to pay higher price to buy goods input from countries out of the Blocs
• May take over local producers
• Workers are often exploited by global companies and paid low wages for long hours