PHYS 114 Midterm II
if Fnet = 0, what is the change in momentum
0
What is Young's modulus?
A measure of stiffness/ how difficult it is to change the shape of a material it is the property of a material
rewrite Hooke's law with the equation for k
F = YA/L x delta L
what is the equation for net force
F = ma
what is stress's equation
F/A
what is Hooke's Law
F=-k*deltax
what is the units of impulse
N x s
how do you calculate impulse
Net Force (F) x Time (t)
what is shear
Shearing forces are unaligned forces pushing one part of a body in one direction, and another part the body in the opposite direction. -can lead to torgue
what is torque
The ability of a force to cause rotation around an axis. it is a measure of how effective a force is at causing an object to rotate
if you increase an animal's size by a factor of X, the stress in its leg bone will increase by what factor
X
what is strain's equation
Y (delta L/L)
what is a perfectly inelastic collision
a collision in which the 2 objects stick together and move with a common final velocity
what is an external force
a force from the surroundings
what is a pliant material
a material that shows large deformation with small ofrces
what is a collision
a short duration interaction between two objects
what is a positive torque
a torque in the counterclockwise direction
what improves stability
a wider base of support and/ or a lower center of gravity
what is a ductile object
an object that can be deformed without breaking
what is a stable object
an object whose center of gravity is over the base of support
what is a rigid material
anything that experiences very small changes in dimension with normal force
where should gravitational torque be applied
at the center of gravity
what is a negative torque
clockwise turn
how do you calculate friction
coefficient of static/kinetic friction * normal force
what two factors influence the length by which it extends when force is applied
cross section initial length
how do you calculate hydrostatic strain
delta volume / volume
where is torque 0 in static equilibrium
everywhere the implication is that you can pick any point you wish as a pivot point to calculate the torque
what is the equation for torque
force (perpendicular)x moment arm (r)
what is restoring force
force that restores a system to an equilibrium systems that exhibit restoring forces are elastic
what is an internal force
forces that act only between objects within a system
what is friction dependent on
friction is dependent on normal force/ not surface area
what is the impulse momentum theorem
impulse = momentum (final) - momentum (i)
how can you calculate Fnet looking at a free-body diagram
in each coordinate, x & y, you subtract the net negative forces from the net positive forces
is an explosion an internal or external force
internal
what does a large K in Hooke's law mean
it is a stiffer spring
what is the impulse approximation
it tells us to ignore small forces during the brief impulse force
is impulse a type of force
it's impulse force, yes which also means it is a vector
what is the formula for k in Hooke's lawa
k = YA/L L: length A: cross section Y: Young's modulus
Beyond elastic limit: what is the linear region what is the tensile strength
linear region: young's modulus tensile strength: breaking point/ failure it is the largest stress the material can sustain before breaking
what is easier to stretch, a longer or shorter material
longer materials
what is more difficult to stop, an object with more or less momentum
more
what causes acceleration
net force
can a Young modulus change for a single material
no
is there torque when an object's center of gravity is directly above the pivot point
no
is there torque when an object's center of gravity is directly below the pivot point
no
is Hooke's law always true when an object is stretched/ compressed
no, if it is stretched/ compressed too far, hooke's law does not apply
is static friction constant
no, it depends on the force applied to an object
do biological materials follow the typical stress strain relationship
no, they have a non-linear stress strain curve
how much torque comes from force applied perpendicular to the radial line
none
what is normal force? how does it prevent us falling through objects
normal force adjusts itself so that the object stays on the surface without penetration
how do you calculate momentum
p = mass * velocity
does Strain include young's modulus
question for class
what are the 5 steps for solving impulse and momentum problems
sketch the system define coordinate define symbols list known info identify unknown
What is k in Hooke's Law?
spring constant, this is dependent on the spring
what direction does spring force point
spring force always points in the direction opposite the displacement from equilibrium
what is stronger at its maximum, the coefficient of static, kinetic, or rolling friction
static > kinetic > rolling
what is the x axis in the stress strain curve
strain
what is the formula for hooke's law using stress and strain
stress = strain
what is hydrostatic stress
stress/ compression from every direction
define the universe
system + surroundings
how is Newton's first law related to Newton's second law
the 1st law is a specific example of the 2nd law
what is impusle
the change in momentum
what force causes torque
the force applied perpendicular to the radial line
what is torque related to
the magnitude of the force the distance between where the force is applied and the pivot point the angle at which the force is applied
what is the ultimate stretch of an object
the maximum an object can stretch before breaking
what is related to the change in momentum of a system
the net force that acts on that sysm
in what direction is rolling friction
the opposite direction of motion
what is apparent weight
the sensation of weight is due to contact force it is the magnitude of supporting contact force
what does it mean when momentum is conserved
total momentum of 2 objects during and after a collision is unchanged impulses are equal and opposite, therefore the change in momentum is equal
when is there a change in momentum in a system
when force is from the surroundings
what is an inelastic collision
when objects stick together
what is an explostion
when particles of the system move apart after a brief intense interaction it is the opposite of collision
what is weightlessness
when someone is in free fall
when is an object at static equilibrium
when the object has a net force of 0 and a net torque of 0
is kinetic friction constant
yes
do objects moving from one momentum to another always have the same impulse
yes, although force and time vary
is biological material elastic
yes, many pliant biological materials have low stiffness and large tensile strength