Quick Review Flashcards - Click to flip and test your knowledge!
Question
What is the primary function of a machine when it acts as a 'force multiplier'?
Answer
It allows a heavy load to be lifted by applying less effort.
Question
Give an example of a machine acting as a force multiplier.
Answer
A jack used to lift a car.
Question
A machine that changes the point of application of effort to a convenient point is exemplified by what part of a bicycle?
Answer
The rear wheel rotated by applying effort to the pedal.
Question
What is the primary purpose of using a single fixed pulley to lift a bucket of water?
Answer
To change the direction of effort to a more convenient direction.
Question
In mechanics, what does it mean for a machine to obtain a 'gain in speed'?
Answer
A greater movement of load is achieved by a smaller movement of effort.
Question
Why can a machine not be used as both a force multiplier and a speed multiplier simultaneously?
Answer
Because a gain in force requires a loss in speed, and vice versa.
Question
Term: Load ($L$)
Answer
Definition: The resistive or opposing force to be overcome by a machine.
Question
Term: Effort ($E$)
Answer
Definition: The force applied on the machine to overcome the load.
Question
What is the formula for the Mechanical Advantage ($MA$) of a machine?
Answer
$MA = \frac{Load (L)}{Effort (E)}$
Question
Why does Mechanical Advantage ($MA$) have no unit?
Answer
It is the ratio of two similar quantities (forces).
Question
If the effort needed is less than the load ($E < L$), the Mechanical Advantage is _____.
Answer
Greater than 1
Question
A machine with a Mechanical Advantage less than 1 ($MA < 1$) is used to obtain a _____.
Answer
Gain in speed
Question
What is the primary use of a machine with a Mechanical Advantage equal to 1 ($MA = 1$)?
Answer
To change the direction of effort.
Question
What is the formula for Velocity Ratio ($VR$) in terms of velocities?
Answer
$VR = \frac{Velocity\ of\ effort (V_E)}{Velocity\ of\ load (V_L)}$
Question
Express Velocity Ratio ($VR$) in terms of displacement of effort ($d_E$) and load ($d_L$).
Answer
$VR = \frac{d_E}{d_L}$
Question
If the velocity ratio of a machine is greater than 1 ($VR > 1$), the machine acts as a _____.
Answer
Force multiplier
Question
What is the definition of 'Work input' ($W_{input}$) for a machine?
Answer
The work done on the machine by the effort.
Question
What is the formula for Work output ($W_{output}$)?
Answer
$W_{output} = Load \times displacement\ of\ load$
Question
Define the efficiency ($\eta$) of a machine.
Answer
The ratio of work output to work input.
Question
What is the formula for efficiency ($\eta$) expressed as a percentage?
Answer
$\eta = \frac{Work\ output (W_{output})}{Work\ input (W_{input})} \times 100\%$
Question
Why does efficiency ($\eta$) have no unit?
Answer
It is the ratio of two similar quantities (work).
Question
What defines an 'ideal machine'?
Answer
A machine in which there is no loss of energy in any manner.
Question
Why is the efficiency of an actual machine always less than 100%?
Answer
Due to energy loss from friction and the weight of moving parts.
Question
State the mathematical relationship between $MA$, $VR$, and $\eta$.
Answer
$MA = VR \times \eta$
Question
For a machine of a given design, which value does not change even if friction increases: $MA$ or $VR$?
Answer
Velocity Ratio ($VR$)
Question
Concept: Lever
Answer
Definition: A rigid, straight (or bent) bar capable of turning about a fixed axis.
Question
What is the 'fulcrum' of a lever?
Answer
The fixed point or axis about which the lever turns.
Question
The perpendicular distance of the line of action of effort from the fulcrum is called the _____.
Answer
Effort arm
Question
State the Principle of a lever (Law of levers).
Answer
$Load \times load\ arm = Effort \times effort\ arm$
Question
How is the Mechanical Advantage ($MA$) of a lever calculated using its arms?
Answer
$MA = \frac{Effort\ arm}{Load\ arm}$
Question
In a Class I lever, where is the fulcrum ($F$) located?
Answer
Between the effort ($E$) and the load ($L$).
Question
Give two examples of Class I levers.
Answer
Seesaw and a pair of scissors.
Question
Which class of lever can have a Mechanical Advantage greater than, less than, or equal to 1?
Answer
Class I lever
Question
When a pair of scissors is used to cut cloth, why is its Mechanical Advantage less than 1?
Answer
The load arm (blades) is longer than the effort arm (handles).
Question
In a Class II lever, which component is located in the middle?
Answer
The load ($L$)
Question
Why is the Mechanical Advantage of a Class II lever always greater than 1?
Answer
Because the effort arm is always longer than the load arm.
Question
Give two examples of Class II levers.
Answer
Nutcracker and wheelbarrow.
Question
In a Class III lever, what is the relative position of the effort ($E$)?
Answer
Between the fulcrum ($F$) and the load ($L$).
Question
Why is the Mechanical Advantage of a Class III lever always less than 1?
Answer
Because the effort arm is always shorter than the load arm.
Question
What is the main advantage of using a Class III lever?
Answer
To obtain a gain in speed.
Question
Give two examples of Class III levers.
Answer
Sugar tongs and a fishing rod.
Question
The action of nodding the head represents which class of lever in the human body?
Answer
Class I lever
Question
Raising the weight of the body on toes is an example of which class of lever?
Answer
Class II lever
Question
The forearm used to raise a load on the palm acts as which class of lever?
Answer
Class III lever
Question
Concept: Single Fixed Pulley
Answer
Definition: A pulley whose axis of rotation is stationary in position.
Question
What is the ideal Mechanical Advantage ($MA$) of a single fixed pulley?
Answer
1
Question
What is the ideal Velocity Ratio ($VR$) of a single fixed pulley?
Answer
1
Question
Concept: Single Movable Pulley
Answer
Definition: A pulley whose axis of rotation is movable (not fixed in position).
Question
In an ideal single movable pulley, what is the Mechanical Advantage ($MA$)?
Answer
2
Question
What is the Velocity Ratio ($VR$) of a single movable pulley?
Answer
2
Question
How does the weight of a movable pulley affect its Mechanical Advantage?
Answer
It reduces the Mechanical Advantage to less than 2.
Question
What is a 'block and tackle' system?
Answer
A combination of several pulleys in two blocks, where the upper block is fixed and the lower block is movable.
Question
In a block and tackle system with $n$ total pulleys, what is the Velocity Ratio ($VR$)?
Answer
$n$
Question
For an ideal block and tackle system with $n$ pulleys, what is the Mechanical Advantage ($MA$)?
Answer
$n$
Question
Formula: Mechanical Advantage of a block and tackle system considering the weight ($w$) of the lower block.
Answer
$MA = n - \frac{w}{E}$
Question
Formula: Efficiency ($\eta$) of a block and tackle system considering the weight ($w$) of the lower block.
Answer
$\eta = 1 - \frac{w}{nE}$
Question
To increase the efficiency of a block and tackle system, the lower block should be as _____ as possible.
Answer
Light
Question
In a pulley system, the work done by the effort is called _____.
Answer
Input energy
Question
In a pulley system, the work done on the load is called _____.
Answer
Output energy
Question
Why does the Velocity Ratio ($VR$) of a block and tackle system remain constant even with friction?
Answer
It depends only on the number of strands of the tackle supporting the load.