Dynamics Notes Flashcards
Newton’s First Law: An object has no forces acting on it. If it is at rest, it will …. If it is moving, it will continue to move in a …. at a ….
remain at rest; straight line; constant speed
If a force is being exerted on an object, you must be able to identify a specific … (…) of that force. A force is not exerted on an object unless there is an identifiable specific …
cause (agent); cause
Net force = …. of forces/ … force
superposition; resultant
a compressed spring exerts a … force on an object
pushing
a stretched spring exerts a … force on an object
pulling
the force of a fluid (gas/liquid) on a moving object is called … and points in the direction … of motion
drag; opposition
drag is large for objects moving at … or in …
high speeds; dense fluids
drag is small for objects that are … and …, moving in air, with a speed that is …
heavy; compact; not too great
thrust: when a jet/ rocket engine …. at ….; force opposite the direction in which …
expels gas; high speeds; exhaust gas is expelled
an object pulled with a constant force moves with a
constant acceleration
the tendency to resist a change in velocity (to resist speeding up/slowing down) is called
inertia
more massive objects have more
inertia
Newton’s Second Law: an object of mass m subjected to forces F1, F2, F3, … (this is not a fill-in the blank) will undergo an acceleration given by: …. where the net force is the vector sum of all forces acting on the object. the acceleration vector points in the same direction as the …
a = ∑F/ m; net force vector
1 N =
1 (kg*m)/ s^2
1 lb = … N
4.45
Newton’s Third Law: every force occurs as one member of an … pair of forces. Defines a force as an ….
action/reaction; interaction
the two members of an action/reaction pair act on two
different objects
the two members of an action/reaction pair point in … and are equal in ..
opposite directions; magnitude
friction that prevents slipping is
static friction
when walking, static friction points in the … direction to prevent your foot from slipping …
forward; backward
friction when walking is static because your feet are not … even though your body is in …
sliding; motion;
cars use static friction to propel themselves as well. Car tires push .. against the road and the road surface then pushes the car tires …
backward; forward
Objects at rest are in …. equilibrium. Objects moving at constant velocity are in … equilibrium
static; dynamic
Your sensation of weight–how heavy you feel– is due to …. (this is …)
contact forces supporting you; normal force
apparent weight (wapp) = magnitude of
supporting contact forces (normal force)
in equilibrium, actual weight and apparent weight
are generally the same
When wapp > w, you feel
heavier
scale readings show
apparent weight
a person/ object in free fall has … apparent weight
zero
weighless does not mean no weight– refers to
no apparent weight
static friction acts in response to an
applied force
higher coefficient of static friction → greater … between object and surface, and the harder it is to make the object …
stickiness; slip
coefficient of static friction applies only to …., as any static friction (besides …) would be equal to the …
max static friction; max static friction; opposing force
magnitude of static friction adjusts itself so that the net force is … and the object doesn’t …
zero; move
magnitude of static friction cannot exceed the ….. If the friction force needed to keep the object stationary is greater than Fs, max, the object … and starts to …
max; slips; starts to move
kinetic friction has a nearly … magnitude
constant
magnitude of kinetic friction force does not depend on how … the object is sliding
fast
a wheel rolling on a surface experiences a form of static friction, as the portion of the wheel that contacts the surface is … with respect to the surface
stationary
objects in contact have the same …
acceleration
a massless string/rope “transmits” a force undiminished from one end to the other: If you pull on one end of a rope with force F, the other end of the rope pulls on what it’s attached to with a force of the ….
same magnitude F.
the tension in a massless string/roe is the … from one end to the other
same
for massless ropes/strings and massless, frictionless pulleys:
if a force pulls on one end of a rope, the tension in the rope equals the magnitude of the …
If two objects are connected by a rope, the tension is the same at both ends.
If the rope passes over a pulley, the tension in the rope is ….
pulling force; unaffected
force diagrams represent a
particular instant in time
If the sum of the forces points in the same direction as the system object’s velocity, the object ….; if it is in the opposite direction, it ….
speeds up; slows down
… reference frame: one in which an observer sees that the velocity of the system object remains unchanged if no other objects exert forces on it or if the sum of all forces exerted on the system object is zero.
inertial
for observers in …. reference frames, the velocity of the system object can change even though the sum of forces exerted on it is zero
noninertial
Newton’s First Law: for an observer in an inertial reference frame when no other objects exert forces on a system object or when the forces exerted on the system object add to zero, the object continues moving at …. (including remaining at ..)
constant velocity; rest
Inertia is the phenomenon in which a system object continues to move at …. when the sum of the forces exerted on it by other objects is …
constant velocity; zero
inertia represents …, is not a …., and expresses a resistance to …
mass; force; acceleration
Newton’s Second Law expresses a cause-effect relationship: force (….) is the cause of … (….)
cause; acceleration; effect
coefficient of static friction is a measure of the relative difficulty of
sliding two surfaces across each other.
Maximum static friction force depends on the … of the two surfaces and on the magnitude of the …. exerted by one surface on the other (same for kinetic friction)
roughness; normal force
the magnitude of the static friction force is always less than or equal to the product of these two quantities:
0 <= fs <= mu * Fn
Under the same conditions, the magnitude of the kinetic friction force is always … than the magnitude of the …
lower; maximum static friction force
Expression for kinetic friction is applicable only for …, not … objects. It also fails for objects moving at …
sliding objects; rolling; high speed
Models for static and kinetic friction assume … and … surfaces
rigid; consistent
