Lecture 3_190606 Flashcards
Newton’s Laws
1) on object in motion stays in motion … at rest stays….
2) until acted on by a force, F(N) = m(kg)*a(m/s^2)
3) for every action there is an equal and opposite reaction
Mass (kg)
m = F(N)/a(m/s^2)
Velocity (m/sec)
v = Δx/Δt
Acceleration (m/sec2)
a = Δv/Δt
Force (kg * m/sec2)
F = m * a
Scalars
magnitude and units, but NOT direction
- distance
- speed
- mass
Vectors
magnitude, units, and direction
- displacement
- velocity
- weight
Fundamental forces
1) nuclear force (strongest)
2) electromagnetic force
4) gravitational force (weakest)
Nuclear force
Strongest
Holds protons & neutrons together in nucleus
Electromagnetic force
Holds electrons in atoms, tries to force protons apart
Gravitational force
Weakest
Holds earth in sun’s orbit and keeps you from floating away
Gravitational constant & Gravity
F.earth = G * m.earth * m / r.earth^2
g ~ 9.8m/s^2
lb vs kg
lb = force
kg = mass
2.2 lb / kg
N
= kgg = kgm/s^2 = force
Scales
measure weight
Balances
measure mass
Density
mass / volume = g/ml = g/cm^3, kg/m^3
density of water = 1g / 1ml
Specific gravity
density of substance / density of water
*unit-less
Pressure
= Force / Area
1 N / m2 = 1 Pa
Atmospheric Pressure
1 atm = 760 mm Hg = 760 Torr = 101.325 kPa = 14.7 psi
= 29.9 inches of Hg
Barometer
Compares atmospheric pressure to a vacuum
Patm = ρ * g * h – density, gravity, height
Manometer
Compares atmospheric pressure to an unknown pressure
ΔP = ρ * g * Δh
Aneroid Bellow Gauge
Use expansion of bellows by pressure
*useful for small or low pressures
Bourdon Gauge Use
coiled tube that “straightens” in response to pressure
*useful for high pressures
Ptotal = Pgauge + Patm
Work
a force acting through a distance
W = F (N) * d (m) – so N * m
1 N * m = 1 J (Joule) = 1 kg * m^2 / sec^2
Energy
The units for energy and work are the same – Joules (N*m or kg * m^2 / sec^2)
Another unit for energy =
1 calorie = energy needed to increase temp of 1g of H2O 1ºC NOTE: the “food” calorie, always written Calorie, is really a kcal (1000 calories). 1 kcal = 1000 cal = 4184 J
Kinetic Energy
KE = ½ * m * v2 = kg * m^2 / sec^2
Potential Energy
PE = m * g * h = kg * m^2 / sec^2
Internal Energy
The total energy of a system (kinetic energy + potential energy)
Potential Energy & Work
Imagine lifting an object
F = m * g
If I lift the object “d” distance up, then W = m * g * d
The increase in potential energy is ΔPE = m * g * d = W
Kinetic Energy & Work
Imagine pushing a car, and accelerating it:
a = F / m
Let’s assume I push with constant force for time, t, the car speeds up
W = ΔKE = ½ m * v.final^2 – ½ m * v.initial^2
Power
= Work / time
1 Watt = 1 J/sec = 1 kg * m^2 / sec^3
Laws of thermodynamics
0) if temp A = temp B, then = thermal equilibrium
1) ΔU = Q + W, change in internal energy = energy put into system + work done on the system
2) Heat flows from hot to cold
3) It’s not possible to reach absolute zero
Q > 0
endothermic process: energy flows into system (appears colder)
Q < 0
exothermic process: energy flows out of system (appears hotter)
W < 0
work done by system (expansion)
W > 0
work done on system (compression)
Heat
a measure of energy
Temperature
related to average kinetic energy of particles
KE = 3 * k * T / 2
Where k is Boltzmann’s constant (1.38E-23 J/K), and T is temperature in Kelvin
*When we increase the average energy per particle, we increase the temperature, and vice versa
Specific heat
energy necessary to change the temperature of 1 g of material by 1 degC
c = Q/(m*deltaT)
Heat capacity
C = Q/deltaT
