Physics Equations Flashcards
Fluids: What is the equation for density and the units?
ρ = m / V where units are kg / m^3
Fluids: What is the “Weight” of a fluid in terms of an equation?
Wfluid = Vρg
ρ = density of fluid g = acceleration by gravity
Fluids: What is specific gravity?
density of a substance relative to water
Specific g = ρ / ρh2o
If something is twice as dense as water it has a specific gravity of 2
Fluids: What is the most simple formula for pressure?
P = F (perpendicular) / A
Fluids: what is the equation for gauge pressure?
Pgauge = ρfluidgD
D - depth from surface
Fluids: For an object immersed under fluid what is the equation for total pressure?
Pgauge + Psurface = Ptotal
where Pgauge = ρfluidgD
Psurface is probably 1 atm
Fluids: Archimedes principle states that the force acting upwards on a submerged object is equal to the weight of the fluid displaced by that object. What force is this and what is it in an equation?
Buoyant force
Fb = ρfluid x Vsubmerged x g
if the object if fully submerged then V is equal to the total volume of the object
Fluids: what is true of an object floating on a liquid?
Fnety = 0
therefore W = Fb
Fluids: What is the relationship of ρ and V for an object floating?
For a floating object W-object = Fb
ρobject x V object x g = ρfluid x V submerged x g
rearrange to find
ρobject V-Submerged
———– = ———————
ρfluid V-object
Fluids: What is flow rate of a fluid measured in?
Volume / time therefore m^3 / s
Fluids: What is the equation for flow rate if speed is constant for any given cross sectional area within the tube?
flow = Av
A = cross sectional area of any given point v = flow speed
m^2 x m/s = m^3 / s
Fluids: What is the law of continuity? What is it’s equation?
continuity = flow rate is constant throughout a pipe.
therefore for two sections f1 = f2
if f = Av then..
A1v1 = A2v2
Fluids: what 4 features make fluid have ideal flow?
- Fluid must be incompressible (ρ cant change)
- Viscosity must be negligible
- Flow must be laminar (no turbulence)
- Flow must be steady (volume/s is constant)
Fluids: for large changes in pressure, are gases ideal flowers?
no, gases are compressible often a high pressures violating an ideal flow law
fluids: What is Bernoulli’s equation?
P1 + ρgy1 + 1/2ρv1(^2) = P2 + ρgy2 + 1/2ρv2(^2)
first term = work
second term = PE
third term = KE
fluids: for fluids exposed to the Air, what is the pressure in Bernoulli’s equation?
Patm
fluids:
For fluids at the same height what is true about pressure and velocity?
For fluids at different heights what is true about pressure?
fluids at the same height are not subject to potential energy in Bernoulli’s equation. (ρgy term cancels)
Therefore, the faster a fluid is going (at the same height) the less pressure (on walls of pipe)
For fluids at different heights, the fluid at the higher height has less pressure.
Electrostatics: what is the value of the elementary charge (e)
1.6 x 10^-19 C
charge is quantized in e’s
Electrostatics: Equation for the electrostatic force felt between two charges?
q1q2
Fe = K ——–
r^2
Where K = 9 x 10^9
Note the equation for force felt between two charges is very similar to force felt between two masses.
m1m2 Fg = G -------- r^2
Electrostatics: true or false, Fe is stronger than Fg
true
Electrostatics: What is sin30? sin45? and cos60?
sin30 = 1/2
sin45 = square-root- 2 / 2
cos 60 = 1/2
Electrostatics: which direction do electric fields move?
they move from positive to negative charges. Therefore if you place a positive charge in an electric field, it will feel a force in the direction of the field.
Electrostatics: what is the equation for the electrostatic force in a defined electric field?
Fe = q x E
E = electric field q = charge
note: if q is positive than Fe is positive therefore it will feel a positive (in direction of field) force
Electrostatics: if you combine Fe = qE and q1q2 Fe = K -------- r^2 What equation do you get?
Kq
E = ——– the units are N / C
r^2
q is the source charge producing the electric field
note that this is very similar to electrostatic force (which includes one extra charge on top)
note: E is a vector. Also, you must account an E for every charge.
Electrostatics: true or false, for any force, Fnet = ma still applies.
True!!
Electrostatics: what is electric potential? what is its equation ?
Electric potential is a scaler field permeating around a charge. Changes to Electric potential influence potential energy.
Kq φ = -------- the units are J / C or Volts (V) r
note that φ is very similar to electric field expect r is not squared (which it is in E) and φ is not a vector (E is)
Electrostatics: true or false, for every charge you must account for that charges personal contribution to total φ and to total E
true, except for φ you only account magnitude not direction.
Electrostatics: what is the equation for electrostatic potential energy?
ΔPEe = q x Δφ = qV
where Δφ and V are the same thing
Electrostatics: what is the relationship between work and ΔPEe?
Work done by the electric field = - ΔPEe = - qV
Electrostatics: what is true of kinetic energy in the absence of non-conservative (drag / frictions / etc.) forces?
ΔPEe = - ΔKE