Lesson 6-8 Flashcards
a branch of physics that studies how energy changes in a system
Thermodynamics
deals with the transfer of energy from one place to another and from one form to another
THERMODYNAMICS
a form of energy that corresponds to mechanical work
Heat
The key concept is that ____ is a form of energy corresponding to a definite amount of ______ _____.
heat, mechanical work
Four elements of fire
Heat, Oxygen, Fuel, Chemical Reaction
3 WAYS BY WHICH HEAT CAN BE TRANSFERRED
Conduction
Convection
Radiation
Heat transfers from molecule to molecule.
Conduction
Heat transfers by the movement of heated particles as in air currents.
Convection
Energy is in the form of heat or light rays is sent out from atoms and molecules as they undertake internal change.
Radiation
4 ESSENTIAL THERMAL PROPERTIES OF WOOD
- THERMAL CONDUCTIVITY
- HEAT CAPACITY
- THERMAL DIFFUSIVITY
- COEFFICIENT OF THERMAL EXPANSION
usually represented by k
THERMAL CONDUCTIVITY
measure of the rate at which heat flows through a specified material
THERMAL CONDUCTIVITY
Expressed as the amount of heat that flows per unit time through a unit area subjected to unit temperature difference
THERMAL CONDUCTIVITY
Units used to measure the heat flow or heat transfer are
W/(m^2/k) or W/(m^2/C)
amount of energy needed to raise the temperature of a specific material by 1 degree celcius
Heat Capacity of wood
factors that affect heat capacity of wood
temperature and moisture content
Measure of how fast a wood can absorb heat from its nearby environment
THERMAL DIFFUSIVITY OF WOOD
It is also defined as the ratio of thermal conductivity to the product of density and heat capacity
THERMAL DIFFUSIVITY OF WOOD
Measures the dimensional changes in wood as affected by changes in temperature.
COEFFICIENT OF THERMAL EXPANSION IN WOOD
The ovendry thermal expansion coefficients of a sample wood are ______ in all sections
positive
If the ovendry thermal expansion coefficients of a sample wood are positive the wood ________/_____ on heating and contracts on cooling.
wood swells or expands
4 ESSENTIAL THERMAL PROPERTIES OF WOOD
- THERMAL CONDUCTIVITY
- HEAT CAPACITY
- THERMAL DIFFUSIVITY
- COEFFICIENT OF THERMAL EXPANSION
Ability to absorb and prevent reflections of sound
Acoustic Property
refers to its capacity to absorb or reflect sound and reduce vibrations
Acoustic Property
If the wood has a high damping capacity, it is an ideal material for _____ _____ in which ______ __ _______.
structural components , vibrations is unwanted.
Wood is acoustic because:
- Presence of pores, vessel lines, and microcapillaries
- Fabricated holes
- Fabricated striations
high porosity wood is effective as a sound-absorbing material because it _____ _ ___ ___ _____.
exhibits a small specific impedance
essential in the design and construction of musical
Fabricated holes
The _____, ____, and ____ of these holes influence the ______, _____, and _____ ____ performance of the instrument
placement, size, and shape / resonance, tone, volume, and overall acoustic
It plays a significant role in determining the final sound.
- craftsmanship of the instrument
How the wood is: - treated
3.shaped
4.assembled
It has a high absorption at high frequencies; effective in reducing echoes.
Softwood
It has a moderate reflection; better for diffusing sound.
Softwood
It has a lower absorption overall; absorbs less high-frequency sound.
Hardwood
It has a high reflection especially at lower
frequencies.
Hardwood
The workability of this wood is more challenging, it is better at low frequencies, heavier and have lower reflection
Hardwood
Unit used to measure sound, named after Alexander Graham Bell.
Decibel
___-___ decibel is the normal level for human.
60-70
___ __ is the maximum for safe volume level for ears.
80 dB
Capacity of wood to withstand induced
vibration by sound waves transmitted
from the outside forces
RESONANCE OF WOOD
Movement of electricity can be classified in two different ways
Direct Current (DC) and Alternating Current (AD)
Deals with the movement or flow of energy in the form of electric charge such as electrons.
ELECTRICAL PROPERTIES OF WOOD
flow of electric charge in one direction.
Direct Current (DC)
flow of electric charge that frequently reverses direction.
Alternating Current (AD).
DIRECT CURRENT (DC) ELECTRICAL PROPERTIES OF WOOD
Resistivity
Conductivity
exhibits how strongly it resists the flow of electric current.
Resistivity
as the MC of wood increases from ovendry to FSP, resistivity _______.
decreases
as the MC continues to increase from FSP to complete MC saturation in wood, the _____ __ _____ _____.
smaller its electrical resistivity
The higher the MC the lower the ______.
Resistivity
reciprocal of electrical resistivity.
Conductivity
wood’s ability to conduct electric current
Conductivity
electrical conductivity of wood _____ as
temperature _____ unlike the conductivity of _____.
increases, increases, metal
the wood conductivity is ___ ___ __ ____ ____ compared to the direction across the grain, and greater in the ____ ____ than in the tangential section
greater along the grain direction, radial section
The AC electrical properties of wood deals with the ______ _____.
dielectric constant
also known as relative permittivity
Dielectric Constant
defined as the ratio of the permittivity of a substance to the permittivity of free space.
Dielectric Constant
the measure of energy per unit volume stored in wood in the form of electric polarization when the material is in a given electric field.
dielectric constant of wood
FACTORS AFFECTING ELECTRICAL PROPERTIES OF WOOD
MOISTURE CONTENT
TEMPERATURE
WOOD TYPE
GRAIN ORIENTATION
IS A WOOD A GOOD CONDUCTOR OR INSULATOR?
Insulator
What do we call the fundamental properties of wood that describes its ability to permit the transmission of an electric field?
Permittivity or Dielectric Constant
Branch of science concerned with the behavior of physical bodies when subjected to forces or displacement, and the subsequent effects of the bodies on their environment
Mechanics
KINDS OF STRESSES IN WOOD
➢COMPRESSIVE
STRESS
➢TENSILE STRESS
➢SHEAR STRESS
A type of stress that develops when a material is subjected to an external force that tends to squeeze or shorten the wood.
COMPRESSIVE STRESS
Exerted on a wood if the force tends to increase or to expand the dimension or volume of the wood.
TENSILE STRESS
Relevant in situations where forces act parallel to the grain, causing adjacent layers of wood fibers to slide or deform.
SHEAR STRESS
Result from forces that tends to cause portions of a wood to move or slide in parallel but opposite direction.
SHEAR STRESS
Referred to as the change in length per unit of length in the direction of stress.
STRAIN IN WOOD
Measure of the deformation or change in the shape of the material that results from the applied force.
STRAIN IN WOOD
usually expressed in pounds per square inch (psi) or in pascals (Newton per square
meter)
Stress
the pressure resulting from a force of one pound-force applied to an area of one square inch.
psi
One (1) psi is equal to _____ pascals, or ____ kg/cm².
6,895 , 0.07
referred to as the change in length per unit of length in the direction of stress
Strain
Resistance of the wood specimen from being deformed when stress is applied
MODULUS OF ELASTICITY
a longer line of MOE means it has a _____ ______ to deformity.
greater resistance
TYPES OF DEFORMATION IN WOOD
ELASTIC DEFORMATION
TOTAL DEFORMATION
When there is a sudden change in the shape of wood when load/stress is applied but the change is recoverable when stress is removed
ELASTIC DEFORMATION
It is the line beyond the stress at proportional limit (red broken lines), where the change in size or shape of the wood when applied with stress is no longer recoverable.
TOTAL DEFORMATION
Applied force
Stress
Deformities
Strain
the wood specimen applied with load/stress parallel to grain has the capacity to withstand the load until it reaches its breaking point
MODULUS OF RUPTURE
Structural element that carries transverse loads
WOODEN BEAMS
A piece of wood which is typically long and squared that can be used as a building material.
WOODEN BEAMS
TYPES OF BEAMS
- SIMPLE BEAM
- CANTILEVER BEAM
- CONTINUOUS BEAM
- OVERHANGING BEAM
- FIXED END BEAM
TYPES OF BEAM LOADING
- DISTRIBUTION OF THE WEIGHT IMPOSED
- LENGTH OF TIME WHEN WEIGHT ARE IMPOSED
DISTRIBUTION OF THE WEIGHT IMPOSED
A. CONCENTRATED LOAD
B. OVERHANGING LOAD
C. DISTRIBUTED LOAD
1.UNIFORMLY DISTRIBUTED LOAD
2.UNIFORMLY VARYING LOAD
LENGTH OF TIME WHEN WEIGHT ARE IMPOSED
A. STATIC LOAD
B. PERMANENT LOAD (DEAD LOAD)
C. SHOCK LOAD
(IMPACT LOAD)
D. ROLLING LOAD
directly support the floor boards.
JOIST
wooden beam that supports the roofing in an inclined position.
RAFTER
the ties are placed in bridge
construction longitudinally.
STRINGER
It is a beam with only one support, either left or right
end, that carries loads or weights on the unsupported
section.
CANTILEVER BEAM
It is a beam that is supported or rests on two or more supports
CONTINUOUS BEAM
a beam that is almost similar to a simple beam where in it supported at two points however the loads are carried on the extended portion.
OVERHANGING BEAM
a beam in which both
ends supports are fixed
FIXED END BEAM
an extent of pressure due to the overlaid weight or due to the external forces acting on the wooden beam
BEAM LOADING
It is a load resting at any point in the entire length of the beam.
. CONCENTRATED LOAD
It is a load resting on the extended portion of the beam.
OVERHANGING LOAD
The weights are spread over the entire length.
DISTRIBUTED LOAD
a load which gradually increases in magnitude upon
a stationary beam.
STATIC LOAD
It is a load where the forces act over a long period of time with no increase in magnitude (floor joist).
PERMANENT LOAD (DEAD LOAD)
- load that is suddenly applied
(ex. Wooden bat that hits the ball).
SHOCK LOAD (IMPACT LOAD)
load resulting from weights in motion or a load that is moving
. ROLLING LOAD
refers to the reactions which the wooden beam has obtained because of applied forces.
MOMENT
branch of mechanics that is concerned with the analysis of loads acting on physical systems (example is wood) that do not experience an acceleration, but rather, are in static equilibrium with their environment.
STATICS
THREE BASIC LAWS OF STATICS
- The sum of all vertical forces is equal to zero.
- The sum of all horizontal forces is equal to zero.
- The sum of all moments is equal to zero.
This equation involves rotation. It states that all the moments (or torques) trying to rotate an object in one direction must equal those trying to rotate it in the opposite direction.
∑𝑀=0
This equation indicates that all the forces acting to the left must equal all the forces acting to the right.
∑𝐻=0
