Midterm
EngSci
Force
Lever
Force & Distance Magnifier
Distance magnifier: bigger movement (to load) from a smaller movement (to effort)
Moment
Definition: A turning effect between the bar and the pivot in a lever
EQUILIBRIUM
principle of moment: anti-clockwise moments=clockwise moments
which means balancing
3 factors of moment
1️⃣Distance (the length of the object to the pivot, in cm or m)
2️⃣force created by the amount of mass (in N)
Moment (Unit usually Ncm | Nm)
Moment(Nm)=Force(N) x Distance(m)
3 parts of a lever
Pivot / Fulcrum (Where the bar rotates about)
Effort (a force you applied to the bar)
Load (weight of an object you lift)
Force magnifier: helps overcome large force (load) using a small force (effort)
Tension
Hooke's Law
Describing that "there is proportionality between the load applied to an object and the extended length of the object"
The Spring Experiment
In a nutshell: The load applied to the spring is proportional to the extension length of the spring.
Pressure
3 factors of pressure
Pressure itself (Unit presented in N/cm2 | N/m2)
force (in N)
Area (of the exerting object)
Pressure (N/m^2) = force (N) / Area (m^2)
Gas
What affects gas pressure?
adding more gas: increases the pressure, because more particles hit the balloon inside
decreasing volume: increases pressure because more collision in smaller space
increasing temperature: increases the pressure because particles move faster
Atmospheric pressure: air around us exerts gas pressure to our body all the time
atmosphere pressure near earth's surface is bigger, because the air particles are pulled by gravity towards the earth. If the particles are together, the pressure is bigger
(Explained using a balloon) the collision of air particles (moving fast) with walls of the container
Definition: a measure of the force exerted by an object or substance over a certain area
Example: Knife (small surface = large pressure)
Liquid
liquid pressure at the bottom is the highest because of increasing weight of water
Motion
3-Newton
BALANCE is an important term
First law of motion: unless an external force is applied, stationary objects will remain stationary, and moving object will continue to move in a straight line at a steady speed
inertia(惯性）- object resist changes to their motion
2-Galileo's Experiement
比萨斜塔实验
thought experiment->you do not need a force to keep something moving!
1-Aristotle's Theory
"When a force is removed, the object will stop."
incorrect. He didn't understand friction
object move only when they're pushed
1-2-3-: chronological order
Compression
only happens in gas, not liquid or solid, because the particles are already very close together
When too compressed, gas turns to liquid (because when the molecules are all together, they loses motion)
can happen inwards and outwards
Diffusion
Definition: The movement of molecules to spread and mix unevenly from a high concentration to a low concentration
What affects the speed of diffusion?
Temperament
increase heat = increase particle movements = diffuse quicker and more evenly
Air Convection(气流）
distributes the particles more quickly = quicker diffusion
Experiments
graph
make the line of best fit
Anomalous result is often caused by inaccuracies in experiments, they should be checked
Chemistry
Concentration + Dilution
e.g. 8 potassium manganate particles in 10 particles of water(44%) --> 8 potassium manganate particles in 14 particles of water(36%) DILUTION
Increase Concentration or Decrease Dilution: Add more solute
For acids, concentrated ones are more corrosive than the diluted ones
Decrease Concentration or Increase Dilution: Add more solvent
solute + solvent -> solution
Concentration or Purity: the amount of solute in the solution
Separation techniques
Decanting
control the "gate" for the speed of letting the solution out from the decanting flask/seperating funnel
Solutions with high density: go to the bottom (vice versa)
In reality it can be done by simply pouring / skimming (吃火锅撇油沫)
Purity / Pure Substance
Marker
The boiling point and the melting point is the marker to identify pure substances
e.g. Experiment: Heating and cooling curve of stearic acid (liquid salol)
the boiling point and melting point of pure substance is always constant
(representation in graph: steadily remain in a certain temperature in a certain amount of time)
Basic concepts
It can be an element or a compound
Element: pure substance made up of only 1 atom or molecule of an element
Works for solutions made up of 2 or more liquids that have different densities and cannot react
Evaporation
Filtration
Magnetism
Chemical Reactions
Making Salts
Method 1: metal compound + acid -> metal salt + water
EG. Lead Oxide + Hydrochloric Acid -> Lead Chloride + Water (PbO + 2HCl -> PbCl2 + H2O)
Method 2: metal carbonate+acid -> metal salt + water + carbon dioxide
EG. Lead Carbonate + Sulphuric Acid -> Lead Sulphate + Water + Carbon Dioxide (PbCO3 + H2SO4 -> PbSO4 + H2O + CO2)
Metal Salts depend on metal components and type of acid
Oxidation
Def: Metal and Oxygen reacts
metal+oxygen->metal oxide
eg. 2Mg + O2 = 2(MgO)
eg. 4Na+O2->2(Na2O)
*uses equation balancing
Characteristics
1- irreversible
2-new substance created
3-Rearrangement of Structure
How to identify if a chemical reaction has taken place: temperature, smell, color, gas/heat given out, pH changes, fizzling (or not), change of property etc.
Precipitation
Def: soluble substance + soluble substance reaching together to produce an insoluble substance(which is the ppt) and a soluble substance
soluble+soluble->insoluble+soluble
You can observe the ppt in these three ways:
1-ring at the top of solution
2-at the bottom
3-sporadic particles in the middle
eg. Sodium Hydroxide + Magnesium Nitrate = Magnesium Hydroxide(insoluble)+ Sodium Nitrate
eg. Potassium Iodide + Lead Nitrate -> Lead Iodide (insoluble) + Potassium Nitrate
Displacement
Def: the metal higher in the reactivity series displaces (push away from compound) the metal in the metal compound that is lower
metal (lower) compound + metal (higher)-> metal (higher) compound + metal (lower)
eg. Iron Sulphate + Zinc = Zinc Sulphate + Iron
The higher the higher element is (in the reactivity series), the bigger the reaction
Acid and Metal Reaction
Method: metal + acid -> metal salt + hydrogen
common acids ->metal salt
Hydrochloric (HCl) -> Chloride
Sulphuric (H2SO4) -> Sulphate
Nitric (HNO3) -> Nitrate
The lower the pH of Hydrogen, the higher the concentration, which means bigger reaction, vice versa
eg. Zinc + Hydrochloric Acid -> Zinc Chloride + Hydrogen (Zn + 2HCl -> ZnCl2 + H2)
eg. Magnesium + Nitric Acid -> Magnesium Nitrate + Hydrogen (2Mg + 2HNO3 -> 2MgNO3 + H2)
"a lit spill will combust with hydrogen with a squeaky pop" (a lit spill is a test for the presence of hydrogen; When brought to a flame, a hydrogen will produce a squeaky pop.
"even though the change we see can be subtle, reaction still happens"
Basic Knowledges
Periodic Table
Mg - Atomic Mass: 24
it's based on the sum of protons and neutrons
Mg- Atomic Number: 12
equals the number of electrons
distribution pattern: 1st layer maximum 2; 2nd layer maximum 8; 3rd layer maximum 8. When the electron exceeds the maximum amount, it's in the next layer
Balance Equations
process of ensuring that the number of atoms of each element is the same on both sides of the equation (The atom is acquired by multiplying the coefficient and the subscript) Penvose: What you start with what you must end with
Inertia
Dilution:addition of solvent, which decreases the concentration of the solute in the solution
Common Elements
transition(al) elements
79-Gold Au
47-Silver Ag
30-Zinc Zn
29-Copper Cu
28-Nickel Ni
27-Cobalt Co
26-Iron Fe
80-Mercury Hg
25- Manganese Mn
7th Group
17-Chlorine Cl
6th Group
16-Sulfur S
8-Oxygen O
5th Group
15-Phosphorus P
7-Nitrogen N
4th Group
50-Tin Sn
6-Carbon C
14-Silicon Si
3rd Group
13- Aluminum Al
2nd Group
20-Calcium Ca
12-Magnesium Mg
1st Group
19-Potassium K
11-Sodium Na
3-Lithium Li
1-Hydrogen H
the property of an object that resists changes in its motion
an object at rest tend to stay at rest
an object in motion tends to keep moving in constant speed in a straight line
pulling force or the ability to stretch
Chromatography
Why pencil line? Pencil cannot be dissolved, while ink can
Can be used to identify different dyes/inks, because every ink's composition is unique, just like finger prints
In a nutshell: 拿个专用纸，铅笔画一条，马克笔点几点，放酒精里，正好到铅笔的刻度，然后静待花开～(上面是Kenny写的，详细过程看P5~)
Distillation
A use for distillation: filtrating unclean substances in seawater （但是效果不咋地）
Simple Distillation
Also used for separating solutions with different boiling points, provided that boiling points differences is greater than 100C
Use it for obtaining a pure solution, or obtaining solvent out of mixture
平民窟办法：Conical flask + Delivery tube (一根玻璃管）+ Test tube + a beaker with full of ice (升降台看情况)
Pig Condenser that costs hundreds of pounds with a delivery arm and a round-bottom flask
Fractional Distillation
in petroleum refineries, crude oil is separated into different fractions based on their boiling points, such as gasoline, diesel fuel, kerosene, and jet fuel (industrial use)
SEE P1
SEE P2
Pivot
click to edit
click to edit
Effort👇
LOAD
a lever is essentially a simple machine or tool (according to pvs)
➡️anti-clockwise turning force
clockwise⬅️ turning force
distance between the LOAD and the PIVOT determines how easy it is to lift the load
because...
fun fact: 10N = 1kg
fun fact: 1N/m^2 = 1Pa
配合key words.doc食用效果更佳哦
Uses a magnet to separate magnetic substances from non-magnetic substance
Common elements in the reactivity series (list of metals arranged in order of their reactivity from highest to lowest)
(most reactive) Potassium
Sodium
Calcium
Magnesium
Zinc
Iron
Tin
Copper
(least reactive) Gold
Silver
“Please stop calling me a careless zebra in the classroom" Sun grunts
Aluminum
Carbon
If the metal in the compound is higher in reacting series then the other metal, no displacement happens
Steps: saturated solution->filter solution (residue, filter paper, funnel, conical flask, filtrate)->evaporate (evaporating dish)
Pure substance: single kind of matter that has a fixed or constant structure and cannot be broken down or transformed into other kinds of matter
Compound: pure substance when two or more elements are combined chemically in a fixed ratio
Def: substance that is added to a sample to help identify or track it. Markers can be used to detect the presence of a particular chemical or to monitor the progress of a reaction.
SEE P3
efficient method for separating solution with different, similar boiling points
SEE P4
SEE P5
Def: technique for separating the components, or solutes, of a mixture
(感兴趣的推荐看）
Why separated? alcohol dissolves the mixture in a fluid solvent called the mobile phase, which carries it through a system on which a material called the stationary phase is fixed, and the constituents travel at different apparent velocities in the mobile fluid, causing them to separate based on the differential partitioning between the mobile and the stationary phases
separate a solvent from a dissolved solid
How? When a solution is heated, the solvent evaporates and crystals of the solute are left behind.
separate insoluble solids from liquids and gases using gravity and the filter medium which allows fluid to pass
SEE P6
SEE P7
colors of metal salts
Iron-green
Copper-blue
Gold-gold
Cobalt-red