Mechanics key terms Flashcards
inertia
the property of an object to resist changes in motion
What does acceleration depend on?
force, friction, inertia
what does friction not depend on?
speed, area of contact
what does drag depend on?
speed, area of contact
mass
the quantity of matter in an object
- also the measure of inertia or sluggishness that the object exhibits, in response to any action impelled upon it
Define weight
the force of gravity upon an object
true or false; acceleration of free fall is independent of the objects’ mass
true
in a vacuum, a coin and a feather fall equally side by side. Would it be correct to say that equal forces of gravity act on both the coin and the feather when it is in the vacuum?
no. these objects accelerate equally not because the forces of gravity are equal but because the ratios of their weights to masses are equal
When does non free fall occur?
when the acceleration is less than g; due to resistive forces
When is terminal speed/velocity reached?
when a= 0
What is Newton’s first law?
every object must continue to be at a state of rest or move in uniform motion in a straight line unless compelled to change by forces impressed upon it
What is Newton’s second law?
F= ma; a= f/m
what is Newton’s third law?
Every action has an equal and opposite reaction
a small mass would have a larger acceleration?
true
a bigger mass would have a smaller acceleration?
true
What is a projectile?
Any object that moves through the air or through space under the INFLUENCE OF GRAVITY
What is the curved path the result of ?
the combination of horizontal and vertical components
true or false; horizontal component of motion is completely independent of the vertical component of motion?
true
What shape is the path of a projectile?
hyperbola
If a projectile was launched how much does it does it drop and when?
vertical distance drops 5m for every 8 km
Question: satellites remain in orbit instead of falling to the Earth because they are beyond the main pull of Earth’s gravity?
No, if moving objects were beyond the pull of gravity, it would move in a straight line and would not curve around the Earth; Satellites remain in orbit because they are being pulled by gravity; not because they are beyond it
true or false; a satellite moves in a circular orbit, moving in a direction perpendicular to the force of gravity that acts on it
true
what would happen to a projectile that is launched with a horizontal speed greater than 8km/s?
it will overshoot a circular path and trace an oval path called an ellipse
why does weightlessness seem to occur?
when two objects accelerate at the same rate
Define momentum (p)?
the property of moving things; inertia in motion
true or false; an object at rest has no momentum?
true; it’s not in motion; momentum is not something an object has but something it can provide
define impulse (I)
change in momentum
true or false; in an interaction, impulses are equal and opposite
true
true or false; whenever you exert a net force, you also exert an impulse
true
When does impulse = momentum
when the initial momentum is zero
is an object brought to rest when impulse = initial momentum?
yes
how do we change the momentum of an object?
we must apply an impulse
What forces can cause an object to accelerate? internal or external forces?
external forces; which are forces applied from outside the system
Is change in momentum possible if there is no external force present?
No
when is momentum conserved (no momentum gained and no momentum lost)
Momentum is conserved in a closed system where no external forces are acting
true or false; momentum is conserved in collisions
true; this means that the net change in momentum of system in colliding objects is unchanged before and after the collision
why is momentum conserved in a collision?
this is because the forces that act DURING the collision are internal forces ( the existing momentum is just redistributed)
what are the two types of collision?
elastic and inelastic
What does elastic collision mean
colliding objects REBOUND without lasting deformation and generation of heat
what does inelastic collision mean?
characterized by lasting deformation or the generation of heat or both
What happens in a perfectly inelastic collision
the objects stick together (however momentum is conserved as well even when colliding objects become entangled
what is energy
the property of system that enables it to do WORK
What is power
rate of work
What is energy measured in?
Joules
Define mechanical energy
the form of energy relative to the position of the interacting bodies (potential energy) or their motion
What are the forms of mechanical energy?
Kinetic energy
potential energy
or both
What is potential energy
the stored energy due to an objects’ position relative to another object
What is gravitational potential energy (GPE)
the potential energy of a body due to elevated positions (GPE = mgh)
define kinetic energy
energy of motion; depends on the reference frame; always positive
true or false; only part of the total work that you do in changing the objects’ KE, the rest is going to heat
true
true or false; WORK is not a form of energy; but a way of transferring energy from one place to another or one form to another
true
What is the law of conservation of energy?
Energy can neither be created nor destroyed; it may be transformed from one form into another ; but the total amount of energy never changes
What is a machine
a machine is device for multiplying forces or simply changing the direction of the forces
What is a fulcrum (imagine a triangle)
a point of support on which lever, rotates
What does a pulley change
the direction of force input
what happens when the fulcrum of a lever is relatively close to the load?
the small input force will produce a large output force. This is because the input force is exerted through a large distance and the load is moved over a corresponding short distance
true or false; the forces acting on a machine can change, but the work input and work output will remain the same
true
define efficiency
the percent of work input put into a machine that is converted to useful work output
what happens when the efficiency of a machine is low
more of the work input is degraded to thermal energy
when does inefficiency occur?
whenever energy in the world around is transformed from one form to another
what happens when energy is transformed?
there is a dilution of USEFUL energy
- the amount of usable energy decreases with each transformation until there is nothing left but thermal energy at ordinary temperature
define RPM
revolutions per minute
Define rotational inertia
- the property of an object to resist changes in rotational state of motion
an object rotating about an axis tends to remain rotating about the same axis unless inferred with by some external influence (torque)
What does rotational inertia depend on?
distribution of MASS
true or false; the greater the distance between the bulk of an object’s mass and its’ axis of rotation, the greater the rotational inertia
true
