phyFinal Flashcards
Vernier caliper precision?
0.01 cm / 0.1 mm
Micrometer precision?
0.001 cm / 0.01 mm
Formula for pendulum time to complete one cycle
2π√((Length of string (m))/(Accleration from gravity))
Relationship between time period (s) and length (m)?
Time period varies as / is proportional to square root of length.
First law of motion?
Every body continues in state of rest/uniform motion unless external force acts on it.
Second law of motion formula with units?
F(N) = m(kg) x a (ms-2)
Define inertia
Reluctance of object to change its state of rest/uniform motion due to its mass.
Define terminal velocity
Maximum velocity of falling object in fluid medium, when air resistance = object weight, resultant force on object 0, object has no acceleration.
Describe parachutist motion
- Person immediately A due to gravity.
- UDF from AR increasing, A/RF decreasing.
- TV: UDF = W, A/RF 0.
- Descent continues at constant TV.
- Parachute opens, increased SA, increased UDF from AR supersedes W, deccel immediately.
- UDF decreasing, A/RF increasing.
- 2nd slower TV: UDF = W, A/RF 0.
- Descent continues at constant slower TV.
Describe how surface area and weight affects terminal velocity.
Same SA, heavier object takes longer time to reach TV, has faster TV.
Same weight, larger SA object takes shorter time to reach TV, has slower TV.
Describe stable equilibrium tilt
Object tilted, CG raised, line of action of force remains in BA, (A)CWM of weight about contact point causes it to return to original position.
Describe unstable equilibrium tilt
Object tilted, CG falls, line of action of force falls outside BA, (A)CWM of weight about contact point topples it.
Describe neutral equilibrium tilt
Object tilted, CG stays at same level, moment of weight about contact point 0, stays in same position.
Define stability
Ability of object to return to original position after it has been tilted slightly.
How to increase stability?
Lower CG (by adding load at BA)
Increase/widen BA
Define moment of a force + formula
Product of force and perpendicular distance from line of action of force to the pivot
Moment(Nm) = F(N) x D(m)
Define prinicple of moments
When body is in equilibrium, sum of CWM about pivot = sum of AWCM about same pivot.
Define conservation of energy
Energy cannot be created or destroyed, can be converted from one form to another or transferred from one body to another, but total amount in an isolated system remains constant.
Formula for gravitational potential energy?
m(kg) x g(nkg-1) x h (m)
Formula for kinetic energy?
1/2 x m(kg) v(ms-1)2
Define energy + unit
Energy: capacity of a body to do work.
Joule: work done by a force of 1 N which moves object through distance of 1 m in the direction of the force.
Define power + unit
Power: rate of doing work / rate at which energy changes from one form to another.
Watt: Rate of energy conversion of 1 J/s
Define pressure + formula for all states
Pressure: force acting per unit area.
Solid: P (Pa) = F(N)/A(m2)
Liquid: P (Pa) = h(m) x ρ(kg/m3) x g(N/kg)
Gas: P(Pa) x V(m3) = nR x T (K)
Define (specific) heat capacity + formulae
Amount of thermal energy needed to raise temperature of (specific: unit mass of) substance by 1K/1C.
C = Q(J)/θ(C or K)
JK-1 or JC-1
C = Q(J)/θ(C or K)/m(kg)
Jkg-1K-1 or Jkg-1C-1
Define latent heat, (specific) latent heat of fusion, (specific) latent heat of vaporisation.
L: energy abosrbed/released by substance during state change, without temperature change.
Lf: amount of thermal energy needed to change (specific: unit mass of) substance from solid to liquid without temperature change.
Lv: amount of thermal energy needed to change (specific: unit mass of) substance from liquid to gas without temperature change.
T constant, why V decrease cause P increase?
When V decrease, no. of air molecules per unit V increase, more frequent collisions between molecules and container walls, avg F of molecules on walls increase, P increase.
V constant, why T increase cause P increase?
When T increase, avg KE of air molecules increase, avg speed of molecules increase, more frequent and vigorous collisions between molecules and container walls, avg F of molecules on walls increase, P increase.
P constant, why T increase cause V increase?
When T increase, avg KE of air molecules increase, avg speed of molecules increase, more frequent and vigorous collisions with container walls, avg F of molecules on walls increase, exerts net upward F on container, P inside container greater than atm P, gas V increase until container P = atm P.
Pascal’s principle?
Pressure applied to an enclosed fluid is transmitted without loss to every part of the fluid and container walls.
Define conduction
Transfer of thermal energy through a medium without it moving.
Describe conduction in non-metals + metals
Both: When heated, particles at heated region gain TE, vibrate more vigorously, collide with neighbouring particles, transferring TE to the next in the medium.
Metals: Mobile electrons gain KE, move more rapidly, collide with atoms in cooler part of the metal, transferring their energy.
Conduction speed for different states and reason?
As state changes from solid to liquid to gas, particles spaced farther apart, less collisions between particles, conduction slower.
Define convection
Transfer of thermal energy through convection currents in a fluid, due to a difference in densities.
Describe convection current in liquid
When liquid at container bottom heated, it expands, becomes less dense than water at top, water at bottom rises, water at top sinks. Difference in water densities in top and bottom sets up convection current.
Define radiation
Transfer of thermal energy by electromagnetic waves like infrared radiation without aid of medium.
Compare Black/dull/rough vs white/shiny/smooth surface’s heat absorption, emission, reflection.
Black/dull/rough
Good heat absorber
Good heat emitter
Poor heat reflector
White/shiny/smooth
Poor heat absorber
Poor heat emitter
Good heat reflector
Describe evaporation and its cooling effect
At liquid surface, liquid molecules with higher KE have enough energy to overcome downward attractive force of other molecules and escape into atmosphere, so avg KE of remaining molecules decreases, temperature decreases,liquidcools.
Two laws of reflection?
Incident ray, reflected ray normal at point of incidence coplanar.
Incident ray angle = Reflection ray ang
Definition and two laws of refraction?
Definition: Bending of light as it passes from one optical medium to another due to speed change.
Incident ray, refracted ray, normal at point of incidence coplanar.
Snell’s Law: for two given media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction r is a constant (refractive index).
Define critical angle and condition for total internal reflection
Critical angle: angle of incidence when angle of refraction is 90°. n = 1/sin C
Total internal reflection occurs when light ray in optically denser medium strikes its boundary with an optically less dense medium, angle of incidence is greater than critical angle.
Scalar vs vector quantity?
Scalar: Physical quantity with magnitude
Vector: Physical quantity with magnitude and direction
c
10^-2
m
10^-3
μ
10^-6
n
10^-9
