OAR Mechanical Comprehension
Exam
What is a lever? - answer A simple machine that provides a mechanical advantage in
carrying loads. Composed of a fulcrum (or pivot) and rigid rod (or beam).
What is the formula for calculating the load or the effort of a lever? - answerW1 x L1 =
W2 x L2 (Weight of the load x distance of the load from the fulcrum = weight of the effort
x distance from the fulcrum to the effort.)
What is a first class lever? - answerA lever where the fulcrum is located between the
force and the load. ie. seesaw
What is a second class lever? - answerA lever where the load (weight) is located
between the force (or effort) and fulcrum. ie. wheelbarrow, bottle opener, nutcracker.
Best suited for carrying heavy loads.
What is a third class lever? - answerA lever where the force is located between the load
and the fulcrum. ie. chopsticks, tweezers. Used for accuracy rather than weight.
What is a gear? - answerA wheel with equally sized and spaced teeth located on the
circumference.
What is the first rule of thumb in meshed gears? - answerAdjacent gears rotate in
opposite directions.
If a gear system has an even number of cogwheels then...? - answerThe last cogwheel
will turn in the direction opposite the first wheel.
If a gear system has an odd number of cogwheels then...? - answerThe last cogwheel
will turn in the same direction as the first wheel.
What is the second rule of thumb in meshed gears? - answerThe velocity of the meshed
cogwheels is proportional to the number of teeth. ie. larger the wheel, the slower it
turns.
What is the equation for calculating the velocity of meshed cogwheels? - answerN1 x
V1 = N2 x V2 (Number of teeth in wheel one x velocity of wheel one = Number of teeth
in wheel two x velocity of wheel two)
Velocity of meshed gears can also be calculated using what? - answerGear Ratio. Gear
ration = n1 over/ n2 = v1 over/ v2
, What are the three types of pulley systems? - answerFixed, moveable, and combined.
What is the friction between components in a pulley system? - answerZero.
What is the transfer of force in a pulley system? - answerMaximum.
What is a fixed pulley? - answerA pulley attached to a surface, like a crane or the
ceiling.
What kind of advantage do fixed pulleys provide? - answerThey provide directional
advantage. They do not provide an advantage in lifting loads. They do not change the
direction of the force, so the force must be used in an upward direction. The ceiling
carries half the load in this instance because the weight is divided equally between both
parts of the rope.
What is a moveable pulley? - answerA pulley attached directly to the load.
What is the ratio of the force required to lift a mass with the moveable pulley system? -
answerThe force required to lift anything is inversely proportional to the distance the
rope is pulled. So if the rope is pulled four inches, the weight is lifted two inches.
What is the force required to lift a weight with a combined pulley system? - answerThe
force required to lift a weight is divided by the number of load-supporting ropes used to
lift the weight (don't count the rope you're using to pull the weight.)
What is the formula for applied force for a pulley? - answerF = W/N ( Force of the user =
weight / number of load supporting ropes)
What is the formula for the length of the rope pulled? - answerL = D x N (length of rope
= vertical distance of rope lifted x number of load supporting ropes)
What are the two arrangements of springs? - answerIn Series and In Parallel
What is an In Series spring? - answerThe tips of the springs are connected to another
and the same force is applied to all three springs.
What is an In Parallel spring? - answerAn arrangement where the springs are attached
to surfaces on both of their sides. The force is divided equally between the springs so
they stretch/compress less.
What is an inclined plane? - answerA flat supporting surface with one end higher than
the other. Used for raising or lowering a load.
Exam
What is a lever? - answer A simple machine that provides a mechanical advantage in
carrying loads. Composed of a fulcrum (or pivot) and rigid rod (or beam).
What is the formula for calculating the load or the effort of a lever? - answerW1 x L1 =
W2 x L2 (Weight of the load x distance of the load from the fulcrum = weight of the effort
x distance from the fulcrum to the effort.)
What is a first class lever? - answerA lever where the fulcrum is located between the
force and the load. ie. seesaw
What is a second class lever? - answerA lever where the load (weight) is located
between the force (or effort) and fulcrum. ie. wheelbarrow, bottle opener, nutcracker.
Best suited for carrying heavy loads.
What is a third class lever? - answerA lever where the force is located between the load
and the fulcrum. ie. chopsticks, tweezers. Used for accuracy rather than weight.
What is a gear? - answerA wheel with equally sized and spaced teeth located on the
circumference.
What is the first rule of thumb in meshed gears? - answerAdjacent gears rotate in
opposite directions.
If a gear system has an even number of cogwheels then...? - answerThe last cogwheel
will turn in the direction opposite the first wheel.
If a gear system has an odd number of cogwheels then...? - answerThe last cogwheel
will turn in the same direction as the first wheel.
What is the second rule of thumb in meshed gears? - answerThe velocity of the meshed
cogwheels is proportional to the number of teeth. ie. larger the wheel, the slower it
turns.
What is the equation for calculating the velocity of meshed cogwheels? - answerN1 x
V1 = N2 x V2 (Number of teeth in wheel one x velocity of wheel one = Number of teeth
in wheel two x velocity of wheel two)
Velocity of meshed gears can also be calculated using what? - answerGear Ratio. Gear
ration = n1 over/ n2 = v1 over/ v2
, What are the three types of pulley systems? - answerFixed, moveable, and combined.
What is the friction between components in a pulley system? - answerZero.
What is the transfer of force in a pulley system? - answerMaximum.
What is a fixed pulley? - answerA pulley attached to a surface, like a crane or the
ceiling.
What kind of advantage do fixed pulleys provide? - answerThey provide directional
advantage. They do not provide an advantage in lifting loads. They do not change the
direction of the force, so the force must be used in an upward direction. The ceiling
carries half the load in this instance because the weight is divided equally between both
parts of the rope.
What is a moveable pulley? - answerA pulley attached directly to the load.
What is the ratio of the force required to lift a mass with the moveable pulley system? -
answerThe force required to lift anything is inversely proportional to the distance the
rope is pulled. So if the rope is pulled four inches, the weight is lifted two inches.
What is the force required to lift a weight with a combined pulley system? - answerThe
force required to lift a weight is divided by the number of load-supporting ropes used to
lift the weight (don't count the rope you're using to pull the weight.)
What is the formula for applied force for a pulley? - answerF = W/N ( Force of the user =
weight / number of load supporting ropes)
What is the formula for the length of the rope pulled? - answerL = D x N (length of rope
= vertical distance of rope lifted x number of load supporting ropes)
What are the two arrangements of springs? - answerIn Series and In Parallel
What is an In Series spring? - answerThe tips of the springs are connected to another
and the same force is applied to all three springs.
What is an In Parallel spring? - answerAn arrangement where the springs are attached
to surfaces on both of their sides. The force is divided equally between the springs so
they stretch/compress less.
What is an inclined plane? - answerA flat supporting surface with one end higher than
the other. Used for raising or lowering a load.
