Mechanical Comprehension Flashcards
_____ can be defined as the capacity to do work.
Energy
The basic unit of work is the _____, and it represents _____.
joule (J); newtons times meters (or kg * m^2/s^2)
Identify the common name for this rule: An object at rest tends to stay at rest, and an object in motion tends to stay in motion at constant velocity unless acted on by an unbalanced force.
Newton’s first law of motion
What is the difference between mass and weight?
Mass is the amount of matter an object has, while weight is the amount of force exerted on the object’s mass by gravity.
As an object falls, its _____ energy is converted to _____ energy.
potential; kinetic
_____ energy is the energy possessed by a moving object.
Kinetic
Rewrite the formula for momentum in order to solve for mass.
m = p/v
What is the formula for work?
w = fd
work = force x displacement
What is inertia?
Inertia is the tendency of objects to resist changes in their motion.
Power is defined as _____ and measured in _____.
the rate at which work is performed; watts (or sometimes horsepower)
What is the formula used to express Newton’s law of universal gravitation?
Force of gravity = ((G)(mass 1)(mass 2)) / distance between objects^2
G is a constant equal to 6.67 * 10^-11
What is the formula for acceleration?
acceleration = change in velocity / change in time
The basic unit of force is the _____, which represents _____.
newton (N); the force required to accelerate 1 kg by 1 meter per second per second: kg * m/s^2
What is the definition of mass?
a measure of the total quantity of matter in an object
Variables are inversely proportional when an increase in the independent variable results in a(n) _____ in the dependent variable.
decrease
In science, the delta symbol (looks like a small triangle) represents _____.
change in a quantity
F = ma is the mathematical formula representing Newton’s _____.
second law of motion
Newton’s third law of motion states that _____.
for every action, there is an equal and opposite reaction
_____ energy derives from an object’s position, shape, or state, rather than from its motion.
Potential
In science, acceleration is often measured in _____.
meters per second per second, or m/s^2
What is the formula for power?
p = w/t
power = work divided by time
What is the formula for momentum?
p = mv, where p = momentum, m = mass, and v = velocity
Acceleration due to gravity is approximately _____ meters per second per second, not counting air resistance.
9.8
The term _____ refers to the total of various pushes and pulls acting on an object.
net force
What are the two types of mechanical energy?
kinetic energy and potential energy
In a wheel and axle arrangement, force is usually applied to the _______ wheel in order to move the ______ wheel. (Choose from either larger or smaller for each blank.)
larger; smaller
What is the formula for calculating torque?
torque = rF, where r represents the length of the lever arm of the object being turned, and F represents a force being applied perpendicularly to that lever arm.
How would you increase the mechanical advantage of a wheel and axle arrangement?
by increasing the ratio of the diameter of the large wheel to that of the small wheel
_____ is the common term for the force that opposes movement through air or liquid.
Drag
What is the formula for calculating pressure applied evenly to a surface?
P = F/A, where P represents pressure expressed in pound of force per square inch, F represents force in pounds, and A represents area in square inches.
What is the formula for calculating friction?
Force of friction = coefficient of static or kinetic friction times the normal for a surface exerts when an object presses against it.
Fluid pressure is also known as _____ pressure.
hydraulic
What unit is used to express kinetic or potential energy, and what does that unit represent?
the joule (J), which represents (kg * m^2)/s^2
What unit is used to express torque?
either the newton-meter or the foot-pound
What is the advantage of a pulley?
A pulley enables someone to lift an object while exerting downward, rather than upward, force.
What does torque measure?
How much a force is able to cause an object to rotate
Liquids are effective at transmitting force because they are difficult to _____.
compress
A wheel and axle arrangement links two wheels of different _____.
sizes
What is the principle of the conservation of mechanical energy?
The principle of the conservation of mechanical energy states that the total mechanical energy (PE + KE) of an object remains constant as long as no other force is applied.
_____ is the term for the ability of a force to cause an object to rotate.
Torque
A _____ is a type of inclined plane that can be moved in order to gain mechanical advantage in lifting, splitting, or tightening objects.
wedge
For any given surface, the coefficient of _____ friction is higher than the coefficient of _____ friction.
static; kinetic
_____ friction prevents an object from moving unless overcome by a sufficiently large force.
Static
What is one horsepower equal to?
550 foot-pounds per second, or 746 watts
Increasing the length of a wedge relative to its height _____ the mechanical advantage provided by the wedge.
increases
When two or more pulleys are arranged to work together, the resulting apparatus is called a _____.
block and tackle
Define mechanical advantage.
Mechanical advantage is the advantage gained by using a mechanism to help transmit force.
When two surfaces rub together, _____ friction results.
kinetic
What does the work-energy theorem say?
The work-energy theorem states that any work done to move an object from a resting position to a certain velocity will be converted into the kinetic energy of that object.
What primarily determines the mechanical advantage of a block and tackle?
the number of pulleys
In hydraulics, Pascal’s law states that _____.
the pressure in any part of an enclosed fluid is the same and points in all directions.
What is the formula for calculating gravitational potential energy?
PE = mgh, where m represents the mass of the object in kg, g is acceleration due to gravity (roughly 9.8 m/s^2), and h is the height of the object in meters.
Torque is ______ proportional to the distance from the center of rotation to the point where the force acts. (Choose from directly or inversely.)
directly
In a third-class lever, where is the fulcrum, and where is the force applied?
In a third-class lever, the fulcrum is positioned near one end of the lever, and an upward force is applied to the middle of the lever in order to life an object positioned on the other end of the lever.
How is a gear ratio determined?
Compare the number of teeth on the larger gear to the number of teeth on the smaller gear.
Torque is directly proportional to _____ and _____.
force; distance
In a hydraulic system, _____ force is applied over a greater distance to produce a greater force over _____ distance.
a smaller; a smaller
If a small gear drives a large gear, the large gear will turn with a _____ speed than the small gear, but _____ will be increased.
slower; torque (or rotational force)
How would you increase the mechanical advantage of a second-class lever?
by moving the object to be lifted closer to the fulcrum, perhaps by making the lever longer.
A ramp is a type of _____.
inclined plane
How would you increase the mechanical advantage of a first-class lever?
by increasing the ratio of the distance between the force and the fulcrum to the distance between the fulcrum and the object to be lifted.
On horizontal surfaces, the normal force is usually equal to _____.
the weight of the object
Static friction only arises in response to an attempt to _____.
move an object along a surface
The most likely place for a cable to snap is nearest ______ (the pulling device / the object being pulled)
the pulling device
A lever pivots upon a(n) ______.
fulcrum
Slippery surfaces have _____ coefficients of both kinetic and static friction.
low
Why is an inclined plane a good solution for a lifting task?
The force required will be less than the force required to lift the object directly.
Aircraft are designed to be sleek to _____ the effect of drag; parachutes are designed with large areas to ____ the effect of drag.
minimize; maximize
No machine is 100 percent efficient because all machines are affected by _____.
friction
In a second-class lever, where is the fulcrum, and where is the force applied?
In a second-class lever, the fulcrum is positioned near one end of the lever underneath it, and the force is applied upward to the other end in order to move an object resting on the lever between the force and the fulcrum.
_____ is the term for the responsive force exerted within an object as the object is stretched.
Tension
Potential energy derives from what and has the potential to do what?
Potential energy derives from an object’s position or shape, and it has the potential to be converted into kinetic energy (that is, energy of movement).
How is the efficiency of a machine defined?
The efficiency of a machine is an expression of how much of the force inputted into the machine is turned into movement or force.
A pulley changes the ____ but not the magnitude of a force.
direction
In a first-class lever, where is the fulcrum, and where is the force applied?
In a first-class lever, the fulcrum is positioned in the middle of the lever. Force is applied to one end of the lever to lift an object on the other end.
What is the formula for calculating kinetic energy?
KE = (1/2)(m)(v^2), where me is mass in kg and v is speed in meters per second
Torque is
A. the degree to which a force causes an object to rotate
B. the same as horsepower
C. a push or pull
D. a force that travels in a circle
A. The degree to which a force causes an object to rotate
Torque results in a twisting motion in an object. This is very different from horsepower (choice B) (the rate that work is done), or force (either C or D).
Speed is different from velocity because
A. speed is measured in metric units while velocity is measured in English units
B. velocity involves both speed and direction
C. speed involves both velocity and direction
D. velocity is a scalar quantity
B. velocity involves both speed and direction
Speed is different from velocity, in that velocity (which is a vector quantity) implies both speed (a scalar quantity and direction.
Compared to a smaller mass, a larger mass requires ____ force to achieve the same acceleration rate.
A. less
B. more
C. the same
D. varying
B. more
The relationship between force, mass, and acceleration is described using the formula F = ma. If mass increases, more force is required to achieve the same acceleration rate.
Which of the following statements about force is NOT true?
A. Force is a scalar quantity
B. Force is a push or pull
C. Greater force results in greater acceleration
D. Smaller masses require less force to achieve the same acceleration as larger masses
A. force is a scalar quantity
Force is a vector quantity. This means that it expresses both magnitude and direction.
Mechanical advantage is the advantage gained by the use of ____ in transmitting force.
A. power
B. a transformer
C. a mechanism
D. an engine
C. mechanism
The definition of mechanical advantage is the advantage gained by the use of a mechanism in transmitting force. For example, a lever and fulcrum can be used to multiply the force applied to an object.
A hockey puck sliding on the ice
A. has no net force acting on it
B. would slide forever if the rink was long enough
C. has speed, but not velocity
D. experiences kinetic friction
D. experiences kinetic friction
A hockey puck experiences kinetic friction (however small) that causes it to lose velocity.
Which of the following statements about weight is NOT true?
A. Weight increases closer to earth’s surface.
B. Weight is totally dependent on mass.
C. Weight is greater on planets with greater mass.
D. Weight varies from location to location.
B. Weight is totally dependent on mass.
This is not a true statement because weight is dependent on both mass and acceleration due to gravity (W = mg).
While attempting to push a heavy box across the floor,
A. the amount of force required to start the box sliding is less than that required to keep it sliding
B. the amount of work being done is not dependent on how far the box moves
C. the coefficient of static friction is dependent on the nature of the surface the box is resting on
D. the mass of the box does not affect the amount of force required
C. the coefficient of static friction is dependent on the nature of the surface the box is resting on
The coefficient of static friction is always greater than the coefficient of kinetic friction. If a force is applied, but the box does not move, no work is being done (W = Fd). The nature of the surface the box rests on will define the coefficient of friction between the box and that surface.
Which of the following represents the mechanical advantage of a wheel and axle system where the driven wheel has a radius of 10” and the drive wheel has a diameter of 5”?
A. 4:1
B. 2:1
C. 1:2
D. 1:4
A. 4:1
The mechanical advantage of a wheel and axle system is determined by the ratio of the radius of the wheel where the force is applied to the radius of the wheel where the force is transferred. In this case, the ratio of the radii is 10:2.5 or 4:1.
If it takes a force of 20 pound to stretch a spring one inch, how much force must be applied to stretch the spring three inches?
A. 180 pounds
B. 60 pounds
C. 20 pounds
D. 6.67 pounds
B. 60 pounds
Three inches of movement multiplied by 20 pounds per inch is 60 pounds of force.
In order to apply more torque to a bolt, a mechanic could
A. use a longer wrench
B. apply less force to the wrench
C. use a shorter wrench
D. move the wrench more quickly
A. use a longer wrench
Torque (twisting force) can be increased by increasing the length of the wrench, or by increasing the force applied to the wrench.
A vehicle travels at a constant speed on the highway. It can be said that
A. its acceleration rate is less than zero
B. the net force acting on the vehicle is zero
C. the force applied by the vehicle’s drive wheels is greater than the forces that act to slow the vehicle
D. it is accelerating at a constant rate
B. the net force acting on the vehicle is zero
In accordance with Newton’s first law of motion, a vehicle traveling at a constant speed has no net force acting on it.
If a vehicle accelerates from a standstill at a rate of 1 m/s^2, its velocity after 10 seconds will be
A. 0.10 m/s
B. 0.10 m/s^2
C. 10 m/s
D. 10 m/s^2
C. 10 m/s
Accelerating at the rate of 1 m/s^2 will result in a velocity of 10 m/s at the end of 10 seconds.
(1m/s^2)(10s) = 10m/s
One pound of force is applied to move an object a distance of one foot. How much work has been done?
A. 1 foot-pound
B. 1 watt
C. 2 foot-pound
D. 1 hertz
A. 1 foot-pound
Using the formula W = Fd, it can be seen that 1 pound of force applied through a distance of 1 foot will result in 1 foot-pound of work being done.
Which of the following statements about energy is NOT true?
A. energy cannot be created
B. The amount of energy in the universe is slowly diminishing.
C. Energy cannot be destroyed.
D. Energy can be converted from one form into another.
B. The amount of energy in the universe is slowly diminishing.
The principle of conservation of energy tells us that the amount of energy in the universe is constant.
Which of the following is NOT a true statement about the principles that underlie hydraulics?
A. Liquids conform to the shape of their container.
B. A liquid can be dramatically compressed in order to increase the amount of force the liquid can transfer.
C. A liquid is effectively incompressible.
D. When pressure is applied to a completely enclosed fluid, this pressure is transmitted to all parts of the fluid and the enclosing walls.
B. A liquid can be dramatically compressed in order to increase the amount of force the liquid can transfer.
Choice B is not a true statement; the use of hydraulic force relied on the fact that liquids are effectively incompressible.
Efficiency of a machine is determined by
A. how much horsepower it can produce
B. how much energy it consumes
C. how much of the source energy is converted into usable energy
D. how long the machine can operate at full output
C. how much of the source energy is converted into usable energy
A machine’s efficiency is expressed as the percentage of the source energy that it converts into usable energy.
In order to hit a baseball so that the ball has greater velocity, the player must
A. hit the ball with less force
B. make contact with the ball for a longer period of time
C. apply more torque to the ball
D. hit the ball so that it travels at roughly a 45 degree angle relative to the ground
B. make contact with the ball for a longer period of time
The velocity at which the ball travels will depend upon the impulse that was applied to it. Impulse is determined by multiplying the force by the amount of time that the force was applied. To increase the impulse, the player should hit the ball with greater force and make contact with the ball for a longer period of time.
