physics

Question 1

physics is all about ?

Answer 1

defining fundamental/measurable quantities N relations between these quantities

Question 2

physics type of quantities

Answer 2

scalar = (scale + ar ) = magnitude
vectors = magnitude + direction

Question 3

common scales of physics (6)

Answer 3

mass, distance, speed, volume, temperature, energy

Question 4

vector symbol

Answer 4

one directional arrow above or a subscript character under variable name
(occasionally, they are in bold letter without arrow)

Question 5

simple diagrams (1 directional) names

Answer 5

object model (scalar) and motion diagram (vectors)

Question 6

graph speeding up or slowing down?

Answer 6

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

Question 7

area under the line(curve) of graph
- area as in geometry
- the shape is towards x-axis

Answer 7

> > 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.

Question 8

slopes between 3 graphs

Answer 8

** 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

Question 9

4 (important) kinematic equations

Answer 9

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 }

Question 10

standard si units

Answer 10

meter m, second s, kilogram kg, kelvin K,
[electric current] ampere A,
[amount of substance] mole mol,
[luminous intensity] candela cd

Question 11

amount of substance

Answer 11

-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

Question 12

kelvin and celsius equation

Answer 12

K = C + 273.15

Question 13

horizontally thrown objects in air
comparison (constant acceleration)

Answer 13

• /\y more, air time greater (acceleration constant)
• /\x more, initial v greater (air time same)
• initial v greater, air time lesser (/\x same)

Question 14

horizontally thrown objects calculation
(known variables without info)

Answer 14

> > 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

Question 15

net force, weight and tension

Answer 15

when moving upward means tension > weight and net force is positive

Question 16

spring n force

Answer 16

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)

Question 17

object sliding down inclined plane

Answer 17

-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.

Question 18

gravitational/inertial/ mass

Answer 18

-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

Question 19

calculation shortcut:
the plane slowly raise to a given degree make object start sliding down. find coefficient

Answer 19

tan (degree)

Question 20

calculation shortcut:
frictionless; an object pulling another off the table from rest.
2 masses given, find speed in given time

Answer 20

a = m_p * g / (m_p + m_o)
v = at

[ m_p = mass pull, m_o = mass object ]

Question 21

calculation shortcut:
pulley between 2 objects release from rest.
2 masses given, find displacement in given time

Answer 21

a = g * (m_h - m_l) / (m_h + m_l)
x = 0.5 a t^2

[ m_h = mass heavy, m_l = mass light ]

Question 22

calculation shortcut:
object pushed from diagonally above moving horizontally.
object mass, friction, diagonal degree given. ask normal force.

Answer 22

N = W + ( F_f * tan(degree) )

[ N=normal force, W=weight, F_f=friction ]

Question 23

vector field

Answer 23

no intersection, curving
tail to head, 1 direction (can turn)

Question 24

4 fundamental forces

Answer 24

-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

Question 25

gravity

Answer 25

6.67 * 10^-11 N (m/kg)^2

Question 26

centripetal acceleration & force

Answer 26

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]

Question 27

forces on object, when an object is being spun at high speed making it stuck to the wall, without floor and ceiling

Answer 27

the normal force is towards middle horizontal.
the friction force is upwards opposite gravity.
force of gravity, downwards.

Question 28

forces on object, pendulum style circular motion

Answer 28

degree slope tension force towards pivot.
force of gravity.

Question 29

forces cause by spring

Answer 29

F = kx
k is spring constant in N/m unit (also known as m/s^2)
x is the change of position (x-x0)

Question 30

graph g as a function of 1/r^2

Answer 30

-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