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Monday, September 1, 2014

Frequently Used Equations of Physics & Physics Formulas

Mechanics
velocityaccelerationequations of motionnewton's 2nd law
v̅ = Δs
Δt
a̅ = Δv
Δt
v = v0 + at∑ F = m a
x = x0 + v0t + ½at2
∑ F = dp
dt
v = ds
dt
a = dv
dt
v2 = v02 + 2a(x − x0)
 = ½(v + v0)
weightcentrip. accel.momentumefficiency
W = m g
ac = v2
r
p = m v
ℰ = Wout
Ein
dry friction
ƒ = μNac = − ω2 r
impulseimpulse–momentumworkwork–energy
J = F̅ ΔtF̅ Δt = m ΔvW = Δs cos θΔs cos θ = ΔE
J = 
dt

dt = Δp
W = 
F · ds

F · ds = ΔE
kinetic energypotential energypower
K = ½mv2
ΔU = − 
F · ds
 = ΔW
Δt
P = dW
dt
gravitational p.e.
ΔUg = mgΔhF = − ∇U = F̅v cos θP = F · v
angular velocityangular accelerationequations of rotation2nd law for rotation
ω̅ = Δθ
Δt
α̅ = Δω
Δt
ω = ω0 + αt∑ τ = I α
θ = θ0 + ω0t + ½αt2
∑ τ = dL
dt
ω = dθ
dt
α = dω
dt
ω2 = ω02 + 2α(θ − θ0)
ω̅ = ½(ω + ω0)
v = ω × ra = α × r − ω2 r
torquemoment of inertiarotational workrotational power
τ = rF sin θI = ∑ mr2W = τ̅ΔθP = τω cos θ
τ = r × F
I = 
 r2 dm
W = 
 τ · dθ
P = τ · ω
rotational k.e.angular momentumfrequencyhooke's law
K = ½Iω2L = mrv sin θ
ƒ = 1
T
F = − k Δx
L = r × pelastic p.e.
L = I ωω = 2πƒUs = ½kΔx2
universal gravitationgravitational fieldgravitational p.e.gravitational potential
Fg = − Gm1m2 r̂
r2
g = − Gm r̂
r2
Ug = − Gm1m2
r
Vg = − Gm
r
orbital speedescape speeds.h.o.simple pendulum
v = √ Gm
r
v = √ 2Gm
r
T = 2π √ m
k
T = 2π √ 
g
densitypressurepressure in a fluidbuoyancy
ρ = m
V
P = F
A
P = P0 + ρghB = ρgVdisplaced
volume flow ratemass flow ratevolume continuitymass continuity
φ = V
t
I = m
t
A1v1 = A2v2ρ1A1v1 = ρ2A2v2
bernoulli's equationaerodynamic dragkinematic viscosity
P1 + ρgy1 + ½ρv12 = P2 + ρgy2 + ½ρv12R = ½ρCAv2
ν = η
ρ
dynamic viscosityreynolds numbermach numberfroude number
η = /A
Δvxz
Re = ρvD
η
Ma = v
c
Fr = v
g
η = F/A
dvx/dz
young's modulusshear modulusbulk modulussurface tension
F = E Δℓ
A0
F = G Δx
Ay
F = K ΔV
AV0
γ = F
Thermal Physics
solid expansionliquid expansionsensible heatideal gas law
Δℓ = αℓ0ΔTΔV = βV0ΔTQ = mcΔTPV = nRT
ΔA = 2αA0ΔTlatent heatmolecular constants
ΔV = 3αV0ΔTQ = mLnR =Nk
maxwell-boltzmannmolecular k.e.molecular speed
− mv2
p(v) = 4v2
m3/2
e2kT
√π2kT
K⟩ = 3 kT
2
vp = √ 2kT
m
v⟩ = √ 8kT
πm
vrms = √ 3kT
m
heat flow ratethermal conductionstefan-boltzmann lawwien displacement law
Φ̅ = ΔQ
Δt
Φ = dQ
dt
Φ = kAΔT
Φ = εσA(T4 − T04)
λmax = b
T
internal energythermodynamic workfirst lawentropy
ΔU = 32nRΔT
W = −
P dV
ΔU = Q + W
ΔS = ΔQ
T
S = k log w
efficiencycoefficient of performance
real = 1 − QC
QH
ideal = 1 − TC
TH
COPreal = QC
QH − QC
COPideal = TC
TH − TC
Waves & Optics
periodic wavesfrequencybeat frequencyintensity
v = ƒλ
ƒ = 1
T
fbeat = fhigh − flow
I = P
A
power levelinterference fringes
β = 10 log I = 20 log P
I0P0
nλ = d sin θ
nλ ≈ x
dL
index of refractionsnell's lawmirrors and lensesspherical mirrors
n = c
v
n1 sin θ1 = n2 sin θ2
1 = 1 + 1
ƒdodi
ƒ = r
2
critical angle
sin θc = n2
n1
M = hi = di
hodo
Electricity & Magnetism
coulomb's lawelectric field
F = k q1q2
r2
E = Fe
q
E = k ∑ q r̂
r2
E = k 
dq r̂
r2
field and potentialelectric potential
 = − V
d
ΔV = ΔUE
q
V = k ∑ q
r
V = k 
dq
r
E = − ∇V
capacitanceplate capacitorcylindrical capacitorspherical capacitor
C = Q
V
C = κε0A
d
C = 2πκε0
ln (b/a)
C = 4πκε0
(1/a) − (1/b)
capacitive p.e.electric current
U = 1 CV2 = 1Q2 = 1 QV
22C2
 = Δq
Δt
I = dq
dt
ohm's lawresitivity–conductivityelectric resistanceelectric power
V = IR
ρ = 1
σ
R = ρℓ
A
P = VI = I2R = V2
R
E = ρ J
J = σE
resistors in seriesresistors in parallelcapacitors in seriescapacitors in parallel
Rs = ∑ Ri
1 = ∑ 1
RpRi
1 = ∑ 1
CsCi
Cp = ∑ Ci
magnetic force
FB = qvB sin θFB = q v × BFB = IB sin θdFB = I dℓ × B
biot-savart lawsolenoidstraight wireparallel wires
B = μ0I
ds × r̂
r2
B = µ0nI
B = μ0I
r
FB = μ0I1I2
r
motional emfelectric fluxmagnetic fluxinduced emf
V = BvΦE = EA cos θΦB = BA cos θ
ℰ = − ΔΦB
Δt
ℰ = − dΦB
dt
ΦE = 
E · dA
ΦB = 
B · dA
gauss's lawno one's lawfaraday's lawampere's law
 E · dA = Q
ε0
∯ B · dA =0
∮E · ds = − dΦB
dt
∮B · ds = μ0ε0 dΦE + μ0I
dt
∇ · E = ρ
ε0
∇ · B =0
∇ × E = − ∂B
t
∇ × B = μ0ε0 ∂E + μ0 J
t
Modern Physics
time dilationlength contractionrelativistic massrelative velocity
t' = t
√(1 − v2/c2)
ℓ' = ℓ √(1 − v2/c2)
m' = m
√(1 − v2/c2)
u' = u + v
1 + uv/c2
relativistic energyrelativistic momentumenergy-momentummass-energy
E = mc2
√(1 − v2/c2)
p = mv
√(1 − v2/c2)
E2 = p2c2 + (mc2)2E = mc2
relativistic doppler effectphoton energyphotoelectric effectphoton momentum
λ0 = ƒ = √ 
1 − v/c
λƒ01 + v/c
E = hfKmax = E − ϕ = h(ƒ − ƒ0)
p = h
λ
schroedinger's equationuncertainty principlerydberg equation
iℏ  Ψ(r, t) = − 2 ∇2Ψ(r, t) + V(r)Ψ(r, t)
∂t2m
Δpx Δx ≥ ℏ 
2
1 = −R 
1 − 1
λn2n02
Eψ(r) = − 2 ∇2ψ(r) + V(r)ψ(r)
2m
ΔE Δt ≥ ℏ 
2
half life
N = N02t


One Dimensional Motion

Time and Distance

By one dimension we mean that the body is moving only in one plane and in a straight line. Like if we roll a marble on a flat table, and if we roll it in a straight line (not easy!), then it would be undergoing one-dimensional motion. There are four variables which put together in an equation can describe this motion. These are Initial Velocity (u); Final Velocity (v), Acceleration (a), Distance Traveled (s) and Time elapsed (t). The equations which tell us the relationship between these variables are as given below.

v = u + at

2 = u 2 + 2as Physics Calculator click for calculator

s = ut + 1/2 at 2

Two and Three Dimensional Motion

Scalar or Vector?

To explain the difference we use two words: 'magnitude' and 'direction'. By magnitude we mean how much of the quantity is there. By direction we mean is this quantity having a direction which defines it. Physical quantities which are completely specified by just giving out there magnitude are known as scalars. Examples of scalar quantities are distance, mass, speed, volume, density, temperature etc. Other physical quantities cannot be defined by just their magnitude. To define them completely we must also specify their direction. Examples of these are velocity, displacement, acceleration, force, torque, momentum etc.

Parallelogram law of vector addition

If we were to represent two vectors magnitude and direction by two adjacent sides of a parallelogram. The resultant can then be represented in magnitude and direction by the diagonal. This diagonal is the one which passes through the point of intersection of these two sides.

Resolution of a Vector

It is often necessary to split a vector into its components. Splitting of a vector into its components is called resolution of the vector. The original vector is the resultant of these components. When the components of a vector are at right angle to each other they are called the rectangular components of a vector.

Rectangular Components of a Vector

As the rectangular components of a vector are perpendicular to each other, we can do mathematics on them. This allows us to solve many real life problems. After all the best thing about physics is that it can be used to solve real world problems.
Note: We will show all vector quantities in bold. For example A will be scalar quantity and A will be a vector quantity.
Let A x and A y be the rectangular components of a vector A
then
A = A x A y this means that vector A is the resultant of vectors A x and A y
A is the magnitude of vector A and similarly A x and A y are the magnitudes of vectors A x and A y
As we are dealing with rectangular components which are at right angles to each other. We can say that:
A = (A x + A y1/2
Similarly the angle Q which the vector A makes with the horizontal direction will be
Q = tan -1 (A x / A y)

Laws of Motion

Newton's laws of motion

Through Newton's second law, which states: The acceleration of a body is directly proportional to the net unbalanced force and inversely proportional to the body's mass, a relationship is established between
Force (F), Mass (m) and acceleration (a). This is of course a wonderful relation and of immense usefulness.

F = m x a Physics Calculator click for calculator

Knowing any two of the quantities automatically gives you the third !!

Momentum

Momentum (p) is the quantity of motion in a body. A heavy body moving at a fast velocity is difficult to stop. A light body at a slow speed, on the other hand can be stopped easily. So momentum has to do with both mass and velocity.

p = mv Physics Calculator click for calculator

Often physics problems deal with momentum before and after a collision. In such cases the total momentum of the bodies before collision is taken as equal to the total momentum of the bodies after collision. That is to say: momentum is conserved.

Impulse

This is the change in the momentum of a body caused over a very short time. Let m be the mass and v and u the final and initial velocities of a body.

Impulse = Ft = mv - mu Physics Calculator click for calculator

Work, Energy and Power

Work and energy

As we know from the law of conservation of energy: energy is always conserved.
Work is the product of force and the distance over which it moves. Imagine you are pushing a heavy box across the room. The further you move the more work you do! If W is work, F the force and x the distance then.

W = Fx

Energy comes in many shapes. The ones we see over here are kinetic energy (KE) and potential energy (PE)

Transitional KE = ½ mv 2

Rotational KE = ½ Iw 2

here I is the moment of inertia of the object (a simple manner in which one can understand moment of inertia is to consider it to be similar to mass in transitional KE) and w is angular velocity

Gravitational PE = mgh Physics Calculator click for calculator

where h is the height of the object

Elastic PE = ½ k L 2

where k is the spring constant ( it gives how much a spring will stretch for a unit force) and L is the length of the spring.

Power

Power (P) is work( W) done in unit time (t).

P = W/t

as work and energy (E) are same it follows power is also energy consumed or generated per unit time.

P = E/t

In measuring power Horsepower is a unit which is in common use. However in physics we use Watt. So the first thing to do in solving any problem related to power is to convert horsepower to Watts. 1 horsepower (hp) = 746 Watts

Circular Motion

Circular Force
In the diagram v is the tangential velocity of the object. a is the centripetal (acting towards the center of the circle) acceleration and F is the centripetal forcer is the radius of the circle and m is mass of the object.
as work and energy (E) are same it follows power is also energy consumed or generated per unit time.

a = v 2 / r

F = ma = mv 2/r

Gravitation

Kepler's Laws

Towards the end of the sixteenth century, Tycho Brahe collected a huge amount of data giving precise measurements of the position of planets. Johannes Kepler, after a detailed analysis of the measurements announced three laws in 1619.
1. The orbit of each planet is an ellipse which has the Sun at one of its foci.
2. Each planet moves in such a way that the (imaginary) line joining it to the Sun sweeps out equal areas in equal times.
3. The squares of the periods of revolution of the planets about the Sun are proportional to the cubes of their mean distances from it.

Newton's law of universal gravitation

About fifty years after Kepler announced the laws now named after him, Isaac Newton showed that every particle in the Universe attracts every other with a force which is proportional to the products of their masses and inversely proportional to the square of their separation.
Hence:
If F is the force due to gravity, g the acceleration due to gravity, G the Universal Gravitational Constant (6.67x10-11 N.m2/kg2), m the mass and r the distance between two objects. Then

F = G m 1 m 2 / r 2

Acceleration due to gravity outside the Earth

Here let r represent the radius of the point inside the earth. The formula for finding out the acceleration due to gravity at this point becomes:

g' = ( r / re )g

In both the above formulas, as expected, g' becomes equal to g when r = re.

Properties of Matter

Density

The mass of a substance contained in unit volume is its density (D).

D = m/V

Measuring of densities of substances is easier if we compare them with the density of some other substance of know density. Water is used for this purpose. The ratio of the density of the substance to that of water is called thepecific Gravity (SG)S of the substance.

SG = D substance / D water

The density of water is 1000 kg/m 3

Pressure

Pressure (P) is Force (F) per unit area (A)

P = F/A

Specific Heat

You may have noticed that metals, for example copper, heat faster than water. You would require 4186 J of heat to raise the temperature of water by 1 degree Celsius. On the other hand 1 kg of copper would zoom to this temperature after it receives only 387 J of heat. It is known that every substance has a unique value of amount of heat required to change the temperature of 1 kg of it by 1 degree Celsius. This number is referred to as the specific heat of the substance. Let Q be the heat transferred to m kg of a substance, thereby changing its temperature by dT. The specific heat c of the substance is defined as

c = Q/mdt

Juggle the expression, and we get the heat transferred from a body to its surroundings or the other way around. This is given by.

Q = m c dT

For example the heat required to increase the temperature of half a kg of water by 3 degrees Celsius can be determined using this formula. Here m, mass of water is 0.5 kg and the dt, the temperature rise = 3 deg C and we know the specific heat of water is 4186 J/kg. So here the heat required will be
Q = 0.5 x 4186 x 3 =6280 J
It is as simple as that !!
he table below gives the specific heat of some common substances
J/kg. o Ccal/g. o C
Aluminium9000.215
Copper3870.0924
Glass8370.200
Gold1290.0308
Ice20900.500
Iron4480.107
Silver2340.056
Steam20100.480
Water41861.00

Electricity

Electricity

According to Ohm's Law electric potential difference(V) is directly proportional to the product of the current(I) times the resistance(R).

V = I R

The relationship between power (P) and current and voltage is

P = I V

Using the equations above we can also write

P = V 2 / R

and

P = I 2 R

Resistance of Resistors in Series

The equivalent resistance (R eq) of a set of; resistors connected in series is

eq = R 1 + R 2 + R 3 + - - -

Resistance of Resistors in Parallel

The equivalent resistance (R eq) of a set of resistors connected in parallel is

1/R eq = 1/R 1 + 1/R 2 + 1/R 3 + - - -






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