Physics Flashcards
what is kinetic energy? how is it calculated? and what is the SI unit?
K= 1/2mv^2
SI unit is J or Joules
what is Joule (J) equal to?
kg x m^2 divided by seconds squared
Kinetic energy is a function of the _______ of speed. If speed doubles, the kinetic energy will ________, assuming the mass is constant.
square
quadrupled
How is gravitational potential energy calculated?
U=mgh
U is potential energy, m is the mass in kg and h is the height
tripling the height or tripling the mass of the object, will do what to the gravitational potential energy?
increase it by a factor of 3
what is elastic potential energy? what is it determined or calculated with?
when springs are stretched or compressed from its equilibrium length, the spring has elastic PE
U= 1/2kx^2
k is the spring constant, x is the measure of displacement from equilibrium
how is total mechanical energy calculated?
E=U+K
U is potential energy and K is kinetic energy
what does the first law of thermodynamics account for?
energy can neither be created nor destroyed- it can only be transfered from onw form to another
what are conservative forces?
path dependent and do not dissipate energy
most commonly they have potential energy associated with them ex: gravtiational and electrostatic forces
what are examples or conservative forces? non conservative forces?
conservative forces: gravity and electrostatic forces. they conserve mechanical energy
nonconservative forces: friction and air restistance. they dissipate mechanical energy as thermal or chemical energy
what is work?
the process by which energy is transferred from one system to another
what forces are capable of doing work?
only forces parallel or antiparallel to the displacement vecotr will do work (that is transfer energy)
work and energy are not the same thing. work is the process by which a quantity of energy is moved from one system to another
when do we say that work was done by the gas and the work is positive?
when a gas expands
when do we say that work was done on the gas and the work is negative?
when a gas is compressed
how do you calculate the work done on or by a system?
by finding the area under the pressure-volume curve
If the volume stays constant as pressure changes then how much work is done?
no work is done because there is no area to calculate
what is the work done on a system in an isovolumetric or isochoric process?
no work is done because the volume is constant as pressure changes
If pressure remains constant as volume changes ( isobaric processes), then how is the area under the curve calculated?
the length of P and the width change in V so with isobaric processes where pressure is constant work is calculated as
W=P x change in V
what is Power? and what are the SI units for it?
a measure of the rate of energy consumption, transfer or transformation per unit time
P= W/t= change in E/t
SI unit is watt (W), which is equal to J/s
power can also be calculated in circuits, resistors and capacitors and it is known as electric power. what is the equation for electric power?
P= IV
I is current and V is electrical potential difference (voltage)
what is the relationship between work and energy?
there is a direct relationship between the work done by all the forces acting on an object and the change in kinetic energy of an object
when one calculates the change in kinetic energy, experieinced by an object, then what is the net work done on or by an object?
the same as the change in kinetic energy
how is the first law of thermodynamics expressed?
the change in systems internal energy (U) is equal to the heat transferred into the system (Q) minus the mechanical work done by the system (W)
change in U= Q - W
when is Q ( heat transferred into the system) positive? and when is it negative?
positive when heat flows into the system
negative when heat flows out of the system
when is W (work done by the system) positive and when is it negative?
positive when work is done by the system (expansion)
negative when work is done on the system (compression)
what does it mean when the change in internal energy is a positive value? when it is a negative value?
positive value: increasing temperature
negative value: decreasing temperature
what is Heat?
the process of energy transfer between two objects at different temperatures and will continue until the two objects come into thermal equilibrium at the same temperature
what is conduction?
the direct transfer of energy from molecule to molecule through molecular collisions. two things need to come in contact in order for energy to be transferred
what is convection?
the transfer of heat by the physical motion of a fluid over a material.
since it involves flow, only liquids and gases can transfer heat by these means
what is radiation?
the transfer of energy by electromagnetic waves. transfer of energy through a vacuum.
how can you determine the heat gained or lost by an object and the change in temperature of that object?
q=mc(delta)T
m is mass, c is specific heat, and delta T is change in temp in C or K
specific heat of water is 4.184 J/g x K
when do phase changes occur?
at a constant temperature and the temperature will not begin to change until all of the substance has been converted from one phase to the other
what are phase changes related to?
changes in potential energy
how do you calculate the amount of heat added or removed for a system experiencing a phase change?
q=mL
q is the amount of heat gained or lost, m is the mass of substance, L is the heat of transformation or latent heat of the substance
what is the corresponding heat of transformation with the phase change of liquid to solid or solid to liquid?
heat of fusion
what is the corresponding heat of transformation with a phase change from liquid to gas or gas to liquid?
heat of vaporization
what is an isothermal process? how does it relate to the equation of the first law of thermodynamics?
change in U = 0 (constant temperature so no change in internal energy)
first law reduces to Q=W
heat equals Work
What is an Adiabatic process? how does it relate to the first law of thermodynamics?
Q= 0 ( no heat exchange)
first law reduces to change in U = -W
what is an Isobaric process?
constant pressure
the normal equation is used: change in U = Q - W
what is an isovolumic process and how does it relate to the first law of thermodynamics?
no change in volume and therefore no work accomplished
also called isochoric
so the change in U= Q
How are the processes indicated on a Pressure-Volume graph?
- isobaric
- isothermal
- adiabatic
- isovolumic (isochoric)
isobaric: horizontal line
isothermal: less steep of a hyperbola
adiabatic: more steep of a hyperbola
Isovolumic: vertical line
***pressure is on the Y axis and Volume is on the X axis
what is density and how is it calculated? what are the SI units for it?
what is the density for water?
p=m/V
p(rho) represents density, m is mass and V is volume
kg/m^3, g/mL, or g/cm^3
waters density is 1 g/cm^3
how is the weight of any volume of a substance with a known density calculated?
by multiplying the substance’s density by it’s volume and its acceleration due to gravity
what is specific gravity and how is it calculated?
when the density of a fluid s compared to that od pure water at 1 atm and 4 degrees C
calculated by p(rho) / 1g/cm^3
what is pressure? how is it calculated and what is the SI unit for it?
pressure is the ratio of the force per unit area
P=F/A
SI unit is the pascal (Pa) which is equivalent to 1 N/m^2
what is absolute (hydrostatic) pressure? and what is the equation for it?
the total pressure that is exerted on an object that is submerged in a fluid. (could be either iquids or gases)
P=Po + p(rho) x g x z
P is absolute pressure, Po is pressure at the surface, p(rho) is the density of the fluid, g is acceleration due to gravity, z is the depth of the object
what is gauge pressure?
the amount of pressure in a closed space above and beyond atmoshperic pressure
Pgauge= P - Patm or absolute pressure - atmospheric pressure
when applying pascals principles, what is important to remember when there is a large area? small area?
the larger the area, the larger the force, although this force will be exerted through a smaller distance
a small force over a small area through a large distance to generate a much larger force over a large area through a smaller distance
what is the equation for work as the product of constant pressure and volume change as in an isobaric process?
W=P x (delta V)= F1d1=F2d2
how is the buoyant force magnitude calculated?
density of fluid times the Volume submerged times gravity.
or
density of fluid times the Volume of fluid displaced time gravity
when will an object float?
if its average density is less than the average density of the fluid it is immersed in
what does surface tension result from?
cohesion, the attractive force that a molecule of liquid feels toward other molecules of the same liquid
cohesion occurs btwn molecules with the same properties