MECHANICAL COMPREHENSION Flashcards
Gear revolutions
- r = (DR)/d ; rd=R*D
- D: # of teeth on gear A
- R: revolutions of gear A
- d: number of teeth on gear B
- r: revolutions of gear B
Hydrometers use floats to measure specific gravity. Specific gravity is the weight of a liquid compared with the weight of the water. The liquid with the highest specific gravity will cause the float to rise higher in the glass tube.
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Levers
- First class: Fulcrum is in the middle (scissors, pliers)
- Second class: Fulcrum is at one end, load is in between (nutcracker, wheelbarrow)
- Third class: Fulcrum is at one end, effort is in between (tongs, tweezers)
Mechanical advantage in pistons
- a2d2=a1d1
- A= area, d=displacement
- Smaller D/ bigger D = mechanical advantage
The farther away the fulcrum is from the resistance arm, the greater amount of force that is required to lift the weight and the higher the resistance arm will travel.
No electricity flows through burnt out bulbs, but a voltimeter can bypass it if connected on both sides. It tells you the total voltage in a circuit.
Current stays the same in series
• Current is constant in series, voltage is not
• Voltage is constant in parallel, current is not
• V=IR (currentresistance=V oltage)
• The circuit with the greater resistance is usually in series, because it forces the current
through all resistors.
In a 2 pulley system, the movable pulley will only move up half the distance, and spin half as
much as the fixed pulley.
If a driver wheel is present, the adjacent wheels will rotate according to how close to the center the driver wheel makes contact with them. The closer to the center, the faster it will move.
To find an rpm necessary
• Take number of rods on the wheel, divide that from the needed contacts per minute. (ex. twice per second = 120 contacts per minute. 10 projection rods on wheel. 120/10=12. must rotate at 12 rpm.
Buoyancy
- The deeper you go with an inflated ball, the more difficult it is to hold it under water.
- The deeper you go with the same ball, the more buoyant the ball is.
Rate of heat exchange is faster through objects of greater temperature difference.
Water flows faster through narrow areas than it does through wider. Think of putting your thumb
on the end of a hose to make it spray
4-Stroke Engine parts
• Intake, Compression, Combustion, Exhaust
Wheel and axle question, such as bucket being raised from well.
- Mechanical Advantage = Radius of Axle to handle / radius of drum
- Make sure you’re using the RADIUS, not the diameter
Pressure
- Pressure = Force / Area
- Fluid pressure
- Atmospheric pressure
Statics and equilibrium
• Moment = Force * Distance
Energy
• The difference between kinetic and potential (and when one converts to the other)
- Potential - energy stored in an object
* Kinetic - energy in motion
Electrical Theory
- V=I*R; Finds voltage drop across a circuit or single resistor
- I=Q/T; Current = charge / time
Current
- Direct - flows continuously in the same direction
* Alternating - periodically reverses direction
Devices for electrical theory
- Ammeter - measures current flow in a circuit
- Voltmeter - measures voltage
- Multimeter - measures both
Units
- Charge = coulomb, C
* Current flow = ampere, A
Power =
volts * amperes
Vise
• Ideal MA = (2pilength of handle)/(pitch of thread)
Newton’s Laws
- First – object in motion will stay in motion, object at rest will stay at rest
- Second – force = mass * acceleration
- Third – for every action there is an equal and opposite reaction
Weight Equation
mass * gravity
Heat Laws and rules
• Convection - occurs in liquids and gases by circulating currents caused by a difference in density
and Equilibrium
• Conduction - occurs in solids and stationary fluids. • Depends on the temperature difference
• Placing salt into water increases the specific gravity of the solution and lowers its freezing point.
• Heating a closed container of boiling water increases the pressure of the water vapor (steam) inside the container and increases the temperature of the water.
• ALWAYS moves from hot object to cold object.
• The rate of transfer is greater for the greater temp difference.
A square metal plate is hanging by 4 wires (one on each corner). One breaks, and it’s hanging by only 3 wires now. Does each wire now carry the same amount of weight, or do the 2 diagonally across from each other hold an equal amount that is more than the lone wolf in the other corner?
• The lone wolf does no support. The 2 diagonals carry it alone.
