physics Flashcards
physics is all about ?
defining fundamental/measurable quantities N relations between these quantities
physics type of quantities
scalar = (scale + ar ) = magnitude
vectors = magnitude + direction
common scales of physics (6)
mass, distance, speed, volume, temperature, energy
vector symbol
one directional arrow above or a subscript character under variable name
(occasionally, they are in bold letter without arrow)
simple diagrams (1 directional) names
object model (scalar) and motion diagram (vectors)
graph speeding up or slowing down?
in position vs time graph:
-if the line is becoming horizontal, slowing down
in velocity vs time graph:
-if it’s going away from x-axis, speeding up
area under the line(curve) of graph
- area as in geometry
- the shape is towards x-axis
> > velocity vs time graph = displacement
acceleration vs time graph
= change in velocity = final velocity - initial velocity
* not velocity!
-it’s easier to calculate if the acceleration(/slope of line) is constant.
-if curve, break them into many rectangles using the x-axis intervals.
slopes between 3 graphs
** the constant diagonal line MUST cross (0,0) unless initial point given cannot do so
-if d vs t graph is going constant to up right,
the v vs t graph has horizontal above x-axis line
-if v vs t graph is going constant to down right,
the a vs t graph has horizontal below x-axis line
4 (important) kinematic equations
v = final velocity, v0 = initial velocity, t= time
s = displacement, va = average velocity, a=acceleration
> [no s] v = v0 + at { from y=mx+b }
> [no v] s = v0 t + 1/2 a t^2
> [no t] v^2 = v0^2 + 2 a s
> [no a] s = t va { va = (v+v0)/2 }
standard si units
meter m, second s, kilogram kg, kelvin K,
[electric current] ampere A,
[amount of substance] mole mol,
[luminous intensity] candela cd
amount of substance
-1 mole of any compound= 6.022 x 10^23 particles
-particles is also molecules
-1 mole of h2o = 1 mole of co2 but
the mass(/other values) of h2o in 1 mole ≠
that of co2 in 1 mole
-hence, use to compare other quantities
kelvin and celsius equation
K = C + 273.15
horizontally thrown objects in air
comparison (constant acceleration)
- /\y more, air time greater (acceleration constant)
- /\x more, initial v greater (air time same)
- initial v greater, air time lesser (/\x same)
horizontally thrown objects calculation
(known variables without info)
> > know:: X: x0 ax (vx=v0x), Y: v0y ay
to know:: X: x vx, Y: y y0 vy, t
- y0 can be zero. if it is, y is negative.
equation: y= 1/2 ay t2, x= vx t, vy = at
net force, weight and tension
when moving upward means tension > weight and net force is positive
spring n force
Fs = kx
Fs: force required to stretched/pressed a spring (N)
k: stiffness of spring (N/m); the bigger this, the harder stretch/press
x: displacement of spring after being stretched or pressed (m)
object sliding down inclined plane
-remember, there is another right triangle in there.
-gravity (g), going vertically downward, is NOT a acceleration. it is a ‘resulted’ acceleration formed from two other accelerations.
-gravity is a DIAGONAL acceleration of horizontal and vertical acceleration. (** you need to visualize this. very important in this type of situation)
-the acceleration along the inclined plane is called A_parallel and the perpendicular to that is, yes, A_perpendicular.
gravitational/inertial/ mass
-inertial mass is best measured using force sensor and/or on frictionless surface
-gravitational mass is best measured using only vertical motion or as close as it can to that only
-in the end they are all ‘mass’ that have the same value
calculation shortcut:
the plane slowly raise to a given degree make object start sliding down. find coefficient
tan (degree)
calculation shortcut:
frictionless; an object pulling another off the table from rest.
2 masses given, find speed in given time
a = m_p * g / (m_p + m_o)
v = at
[ m_p = mass pull, m_o = mass object ]
calculation shortcut:
pulley between 2 objects release from rest.
2 masses given, find displacement in given time
a = g * (m_h - m_l) / (m_h + m_l)
x = 0.5 a t^2
[ m_h = mass heavy, m_l = mass light ]
calculation shortcut:
object pushed from diagonally above moving horizontally.
object mass, friction, diagonal degree given. ask normal force.
N = W + ( F_f * tan(degree) )
[ N=normal force, W=weight, F_f=friction ]
vector field
no intersection, curving
tail to head, 1 direction (can turn)
4 fundamental forces
-gravity (attractive force b/t obj with mass)
-weak interaction or weak nuclear force
(force causes neutron to turn into proton)
10^25 * gravity
-electrostatic/electromagnetic force
(attractive/repulsive force b/t charged obj)
10^36 * gravity
-strong nuclear force
(inside atom, force b/t protons in nucleus)
10^38 * gravity
gravity
6.67 * 10^-11 N (m/kg)^2
centripetal acceleration & force
a = linearV^2/r = rangularV^2
linearV=rangularV
-the thing moving in circle is not because there is external force making them move, it’s the gravity and tension towards the pivot what’s causing them to move
v = 2 pi r / T
[T is called period here. time needed to go the whole trip in circular]
forces on object, when an object is being spun at high speed making it stuck to the wall, without floor and ceiling
the normal force is towards middle horizontal.
the friction force is upwards opposite gravity.
force of gravity, downwards.
forces on object, pendulum style circular motion
degree slope tension force towards pivot.
force of gravity.
forces cause by spring
F = kx
k is spring constant in N/m unit (also known as m/s^2)
x is the change of position (x-x0)
graph g as a function of 1/r^2
-this mean g is on y-axis and x-axis has 1/r^2
-by the equation g= GM/r2, we should see
g = (GM) (1/r2) | compare y=mx
this means the slope is GM
