basic physics Flashcards
what is meant by matter?
anything that occupise space and has weight
what are the three basic physical state in which matter can exist?
solid, liquid, and gas
what is meant by pressure?
force that acts on a unit of area
what is the standard sea level atmospheric pressure expressed in inches of mercury and in pounds per square inch?
29.92 inches of mercury and 14.69 pounds per square inch
what characteristic of the atmosphere determines the speed of sound
its temperature
what is meant by the fulcrum of a lever?
the point about which the lever rotates
give an example of a first-class lever, a second-class lever, and a third-class lever
1st - a screwdriver being used to pry the lid from a can of paint
2nd - a wheel barrow
3rd - a hydraulically retracted landing gear
what formula is used to find the amount of work done when an object is moved across the floor?
work = force * distance
what determines the mechanical advantage of an arrangement of ropes and pulleys?
the number of ropes that support the weight
what determines the mechanical advantage of a gear train?
the ratio between the number of teeth on the drive gear and the number of teeth on the driven gear
what is meant by the resonant frequency of an a/c structure?
the frequency that produces the greatest amplitude of vibration in the sturcture
what is the principle upon which ultrasonic inspection is based?
any fault within a material will change the materials resonant frequency. comparing the resonant frequency of a known sound material with the material under test will indicate the presence of a fault
what are two types of fluids?
liquid and gaseouse
what is meant by the density of a fluid?
the mass-per-unit volume of the fluid
what is meant by the specific gravity of a fluid?
the ratio of the density of the fluid to the density of pure water
what effect does the increses in temperature of a confined gas have on its pressure
when the volume of a gas remains constant, an increase in its temperature increases its pressure
what effect does an increase in the volume of a gas have on its temperature if its pressure remains constant?
as the volume of gas increase with a constant pressure, the temperature decreases
what effect does the increase in the pressure of a confined gas have on its temperature?
increasing the pressure of a confined gas increases its temperature
what is the difference in the fluids used in a hydraulic system and those used in a pneumatic system?
fluid used in a hydraulic system is incompressiible. fluid used in a pneumatic system is compressible
what effect on density altitude is caused by an increses in air temperature
as the temperature increases, the air density decreases and the density altitude increases
what effect does an increase in density altitude have on engine performance?
as density altitude increases, air density decreases and engine performance decreases
what effect does high humidity have on piston engine performance?
water vapor is less dense than dry air and thus high humidity decreases the density of the air. the less dense air decreases engine performance
what dies the specific gravity of the electrolyte of a lead-acid a/c battery indicate?
the amount of acid relative to the water in the electrolyte. this is an indication of the state of change of the battery
how much force is produced by 1,000 psi of hydraulic pressure acting on a piston with an area of 20 square inches?
20,000lbs
what will happen to the pressure of a confined gas if the temperature of the gas is increased?
the pressure will increase
what is meant by a temperature of absolute zero?
the temperature at which all molecular movement stops
what is the celsius equivalent of a temperature of 50 degrees F
10 degrees celsius
what are three methods of heat transfer?
conduction, convection, and radiation
what is meant by the absolute humidity of the atmosphere?
the actual amount of water that is in a given volume of air
what causes ice to change into liquid water?
the absorption of heat
what happens inside a solid material when it absorbs heat energy?
the molecules within the material move faster
what is the basic unit of heat in the English system?
British therrmal unit
how much work will one Btu of heat energy perform?
778 foot-pounds of work
what is the basic unit of heat in the metric system?
calorie
how much heat energy is in a small calorie?
the amount of heat energy that will raise the temperature of 1 gram of water 1 degree C
how much heat energy is in a large calorie (Calorie)?
the amount of heat energy that will raise the temperature of 1 kilogram of water 1 degree C
what is the first law of thermodynamics?
heat energy can neither be created nor destroyed, it can only be changed in its form
what is the second law of thermodynamics?
heat energy can only flow from a body having a high temperature to a body having lower temperature
what is an example of heat transfer by conduction?
removal of heat from an engine cylinder by air flowing over its surface
what is an example of heat transfer by convection?
the uniform heating of the air in a room by a floor heater. the heated air rises and forces the cooler air down so it can be heated by condution
what is an example of heat transfer by radiation?
the heating of the earth’s surface by heat transmitted through space form the sun
why do most metals expand when they are heated?
as heat is absorbed, the electrons move faster and expand their orbits in the molecules of the metal
what is meant by the density of air?
the weight of a given volume in air
what is meant by relative wind with regard to an airfoil?
the direction the wind strikes an airfoil
what is meant by the angle of attack?
the acute angle formed between the chord line of the airfoil and the direction the air strikes the airfoil
what is meant by the critical angle of attack?
the highest angle of attack at which the air passes over the airfoil in a smooth flow. above the critical angle of attack the airflow breaks away and becomes turbulent
what is meant by the stagnation point of an airfoil?
the point on the leading edge of an airfol at which the airflow separates, some flowing over the top and some over the bottom
what is the difference between speed and velocity?
speed is the rate at which an object is moving. velocity is the vector quantity that expresses both the rate and direction an object is moving
what is meant by air density?
the mass of air in a given volume
what is meant by weight?
the measure of force of gravity acting on a body
what is meant by thrust?
the forward aerodynamic force produced by a propeller, fan, or turbojet engine as it forces a mass of air to the rear, behind the airplane
what is meant by drag
the aerodynamic force acting in the same plane as the relative wind striking an airfoil. drag acts in the direction opposite to that of thrust
what is meant by auto-rotation in a helicopter?
the aerodynamic force that causes a helicopter rotor to spin with no engine power applied to the rotor system
what is meant by dissymmetry of lift produced by a helicopter rotor?
the difference in lift between the two sides of the rotor disc when the helicopter is in forward flight. the side with the advancing blade produces the greater lift because the forward speed adds to the rotor speed. the side with the retreating blade produces less lift because the forward speed subtracts from the rotor speed.
what is meant by a blade stall of a helicopter rotor?
a condition of flight in which the retreating blade is operating at an angle of attack higher than will allow for the air to flow over its upper surface without turbulence
what is meant by translational lift in a helicopter?
the additional lift produced by a helicopter rotor as the helicopter changes from hovering to forward flight
what is meant by ground effect in helicopter flight?
an increase in lift when a helicopter is flying at an altitude of less than half the rotor span. this increase is produced by the effective increase in the angle of attack caused by the deflection of the down washed air.
what is meant by ground resonance in a helicopter?
the destructive vibration that occurs when the helicopter touches down roughly and unevenly. the shock throws a load into the lead-lag hinges of the rotor blades and causes them to oscillate about his hinge. if the frequency of this oscillation is the same as the resonant frequency of the fuselage, the energy will cause the helicopter to strike the ground hard with the opposite skid or wheel. if corrective action is not taken immediately, ground resonance can destroy a helicopter
