Forces, Energy, Reactivity, Electricity, Rates of Reaction, Photosynthesis, Sound, Space, Genes & Inheritance Notes

Introduction To Density

Density is defined as mass per unit volume: $density = \frac{mass}{volume}$
An object will sink in water if it is more dense than water, and float if it is less dense than water.
Gases are generally less dense than liquids because particles are further apart.
The density of a gas increases when the gas is compressed because the same number of particles occupies a smaller volume.

Ways To Calculate Volume

Way 1 (for regular blocks):
1. Measure the length, width, and height of the block.
2. Multiply the three measurements together to get the volume.
Way 2 (for irregular blocks):
1. Pour a certain amount of water into a measuring cylinder.
2. Place the irregular block into the measuring cylinder.
3. Observe the change in volume.
4. Subtract the initial volume from the final volume to determine the volume of the object.

Heat and Temperature

Heat is the total thermal energy of vibrating particles in an object.
Temperature is the average energy of the vibrating particles in an object.
Thermal energy is measured in joules.
When the thermal energy of an object increases, the particles vibrate faster, increasing the energy in the particles.

Conservation of Energy

When energy is conserved, the total quantity of energy remains the same, even when energy is stored, changed, transferred, or dissipated.
The total energy input to a system is equal to the total energy output.
Example of an energy diagram: Light energy is considered useful, while thermal energy is often wasted. If 10% of the energy is useful, 90% is wasted.

Law of Conservation of Energy

Energy cannot be created or destroyed, but it can be changed, transferred, or dissipated.

Moving from Hot to Cold

When you hold a hot drink, heat transfers to your hands because the drink has a higher temperature than your hands.
Thermal energy always moves from hotter places to colder places.
When thermal energy is removed from a hot object, it dissipates.

Feeling Cold

Cold is not an energy store and cannot move; it represents a lack of thermal energy.
Thermal energy transfers away from your hands to the ice when you hold ice.
You feel cold because thermal energy is leaving your hands.

Conduction

Vibrating particles push against neighboring particles, causing them to vibrate more vigorously.
Conduction works best in solids.
Metals are good conductors of heat, whereas wood and plastic are poor conductors (insulators).
Conductors allow heat to pass through, while insulators do not.

Convection

When a gas or liquid is heated at the bottom, the particles vibrate and take up more space, becoming less dense and rising.
This upward movement is called convection.
The movement around the heated liquid or gas is called a convection current.
Convection cannot happen in solids.

Radiation

Thermal energy transfer via radiation can occur very quickly.
The hotter the object, the more radiation it emits.
Radiation can pass through a vacuum.
Dull, black, and large surface areas are the best emitters and absorbers of radiation.
Shiny, white or silver, and small surface areas are the worst emitters and absorbers of radiation.

Evaporation

Evaporation is the change of state from liquid to gas.
When the particles with the highest energy escape from the liquid, the average energy of the remaining particles decreases.
Different liquids have different forces holding their particles together.
Perfumes evaporate quickly because they have weaker forces between their particles, allowing them to be smelled.

Reactivity Series

The reactivity series lists metals in order of their reactivity:

Most Reactive: Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Zinc (Zn), Iron (Fe), Copper (Cu), Silver (Ag), Gold (Au): Least Reactive

Displacement Reactions

Example: $CuSO4 + Fe \rightarrow FeSO4 + Cu$
Iron displaces copper in copper sulfate, forming iron sulfate.
A more reactive metal will displace a less reactive metal in a reaction.
This reaction is called a displacement reaction.

Using the Reactivity Series

Example: Aluminium + iron oxide → Aluminium oxide + Iron.
This reaction is exothermic.
The heat produced is so high that the iron produced is molten.
The molten iron can be reshaped; this process is also known as the thermite reaction.

Carbon Displacement

Carbon can displace some metals, such as zinc, iron, tin, or lead.
Iron ore is mainly made of iron oxide.
Pure iron is made by combining iron oxide and carbon.

Salts

Hydrochloric acid (HCl) forms chlorides.
Sulfuric acid ( $H2SO4$ ) forms sulfates.
Nitric acid ( $HNO_3$ ) forms nitrates.

Making Salts

Metal + Acid:
- $Acid + Metal \rightarrow Salt + Hydrogen$
Metal Oxide + Acid:
- $Metal Oxide + Acid \rightarrow Salt + Water$
Some metals will not react with acids; alternative methods are required for unreactive metals.

Other Ways of Making Salts

Carbonates, such as calcium carbonate, are salts formed by the reaction of a metal with carbonic acid.

Neutralization

The general equation for neutralization is:
- $ACID + ALKALI \rightarrow SALT + WATER$
Alkalis react with acids to neutralize them, producing a salt.

Metal Oxides and Bases

Soluble metal bases form alkalis when they dissolve in water.
Some metal oxides are not soluble in water and do not form alkalis, but they can still react with acids to form salts.
Metal oxides are called BASES.

Rearranging Atoms

Rearrangement of atoms refers to how atoms change their positions and bonding during a chemical reaction.
The atoms themselves don't change -- only their bonding changes.
New substances with different properties are formed.

Law of Conservation of Mass

The number of atoms before and after a reaction stays the same.
Nothing is lost or created -- just rearranged!
This is called the Law of Conservation of Mass.

Examples

$Iron (Fe) + Oxygen (O2) \rightarrow Iron Oxide (Fe2O_3)$
$2Na + Cl_2 \rightarrow 2NaCl$

Parallel Circuits

Series circuits:
- Only one path for current flow.
- Current is the same throughout the circuit.
- Current flows from one component to another.
Parallel circuits:
- Multiple branches of current flow.
- Components in the branches are connected in parallel.
- Current in all shared branches adds up to the total.

Parallel Circuit Examples

A1 is the same as A4.
A2 and A3 add up to A1 and A4.
Total current is $3.5A \rightarrow 1A + 2A + 0.5A = 3.5A$
Current may differ according to the components on the branches.
If one current is missing, subtract the total current with the remaining ones.

Advantages of Parallel Circuits

The current through a branch can keep flowing, even if the current stops flowing in other branches.
If a component in one branch stops working, the other branches are not affected.
Components in the same circuit can be switched on and off independently.

Current and Voltage in Parallel Circuits

Voltage is linked to electrical energy in circuits.
It's related to the electrical energy supplied to a circuit.
Measured in volts (V) and have voltage ratings.
Measure with a voltmeter.

Voltmeter

Measures voltage.
Measures the energy difference either side of a component.
Connected in parallel with the component.

Voltage in Series Circuit

Voltage across all components adds up to the total supplied voltage.
The amount of voltage shared through components may differ depending on the components.
Adding more components means they will get a lesser share of the voltage.
Increasing cells also increases voltage.

Voltage and Current in Parallel Circuit

Voltage across each branch equals the voltage of the supply.
Adding more components to any one branch will decrease the current in that branch.
Adding cells to a parallel circuit increases the voltage and current across each branch.

Resistance

Measure of how easy or difficult it is for electrons to move through a material.
Resistance is measured in units called ohms (Ω).
Conductors such as copper have low resistance.
Insulators such as most plastics have high resistance.

Ohm's Law

Voltage = Current x Resistance
$V = I \times R$
V - voltage/volts
I - current/amps
R - resistance/ohm

Resistors

A type of electrical component designed to have a known resistance.
Many resistors have colored bands; the colors form a code to show the resistance value in ohms.
The circuit symbol for a resistor indicates its function in a circuit.
The value of the resistor is written with the circuit symbol, including the unit R.

Practical Circuits

Variable resistors can change resistance.
Examples include dimmer switches for lamps and volume controls for music players.
The symbol for a variable resistor is similar to that for a fixed resistor but includes an arrow through the symbol.

Everyday Circuits

Electric circuits are used in many places like homes and schools.
Cars feature warning sounds when headlights are left on.
When a lamp with a low voltage rating is used in a circuit with a high voltage battery, a resistor can ensure it works properly.

Rates of Reaction

$F1 = G \frac{m1 m_2}{d^2}$
$E=mc^2$

Why does the rate of reaction change?

At the start of the reaction, there are many particles that have not reacted, causing collisions to those who have already reacted, consuming more carbon dioxide.
As the particles react, the number of unreacted particles decreases, lowering the chance of 2 unreacted particles colliding with each other, and thus less carbon dioxide is consumed.

Measuring the Rate of Reaction

High concentration or high pressure corresponds to a higher rate, while low concentration or low pressure corresponds to a lower rate.

Surface Area and the Rate of Reaction

More surface area leads to more effective collisions, increasing the rate of reaction.

Temperature and the Rate of Reaction

The higher the temperature, the faster the collisions will happen.

Concentration and the Rate of Reaction

Lower Concentration: Fewer particles to collide means less collisions, fewer successful collisions, results in less product made in the same time, a slower rate of reaction.
Higher Concentration: More particles to collide means more collisions, a greater chance of successful collisions results in more product made in the same time, a faster rate of reaction.

Photosynthesis

Word equation: Water + Carbon Dioxide → Glucose + oxygen
Chemical equation: $6H2O + 6CO2 \rightarrow (sunlight) \rightarrow C6H{12}O6 + 6O2$
Sunlight is collected for photosynthesis by chlorophyll, a green pigment located in chloroplasts.

Importance of Photosynthesis

Provides oxygen: The only source of oxygen on Earth’s surface are from plants. All living organisms require oxygen for respiration.
Provides food and energy: Energy in sunlight is used by plants. Carbohydrates contain some energy that was in sunlight. Most food sources in food chains are from plants making glucose. Without them, food is scarce for the entire world.

More about Photosynthesis

Plant cells contain chlorophyll within chloroplasts that enable photosynthesis, allowing carbon and water to react.
Leaves are very thin, so it is easy for sunlight to reach the cells inside the leaf
Chloroplasts needs plenty of water to make photosynthesis
Gas is easily diffused through air and between the cells

Important Minerals for Plants

Magnesium is needed to make the green pigment in plants (chlorophyll), allowing plants to convert carbohydrates into proteins.
Nitrate is also essential

The Carbon Cycle

Carbon (C) is a non-metal and part of many compounds that make up cells
Examples: diamonds and graphite
All organisms and decomposers respire.
Fossil fuels take a long time to break down.
Dead organisms' fossil fuels contain carbon from fat, protein, and carbohydrates.
Burning fossil fuels releases carbon through combustion.

Climate Changes

Greenhouse gases, such as Carbon dioxide and methane, are increasing due to human activities.
Climate change is a long-term pattern that changes over decades to centuries.

Introduction to Sound

How is sound produced? Through the vibration of particles.
How is sound propagated? By the vibration of particles parallely to the direction of the wave - longitudinal wave.
Speed of sound: Solid: 5000m/s, Liquid: 1500m/s, Gas: 330m/s

Loudness and Pitch

Loudness is indicated by amplitude.
Pitch is indicated by frequency.
Hz/Hertz is the unit for frequency, e.g., 200Hz means 200 waves in 1 second.

Reinforce and Cancellation

Waves reinforce when peak meets with peak or when trough meets with trough.
Waves cancel when peak meets with trough.

Examples of Waves

Light waves ripple on a water surface.
S-waves, sound waves.
Transverse wave: vibrations of particles are perpendicular to the direction of travel. Example slinky moving up and down
Longitudinal wave: vibrations of particles are parallel to the direction of travel. Example slinky moving back and forth.

Formation of the moon

The Fission theory The Capture theory The Collision theory/ Giant impact hypothesis
The Fission theory: moon was formed by splitting away from Earth -4cm/per year of the moon splitting away.
The Capture theory: captured by gravitational energy. Evidence that supports:
The Collision theory:Earth collided w/ a protostar called Theia Dust & gases formed the moon
the composition of rocks are the same the theory fits w/ how the theory of solar system is formed.
Evidence that is against: composition of moon should be more similiar to Theia than Earth surface of Earth doesn’t appear to be molten despite the high temperature from the giant impact.

Nebulae

clouds of dust & gases & where stars are formed. made w/ Hydrogen gas & Helium gas.
Orion Nebulae = Northern atmosphere
Carina Nebulae = Southern atmosphere

Tectonics

earthquake, tsunami & volcano eruptions are all caused by the movement of tectonic plates
when the mantle near the core is heated, the hot mantle rises up, forming volcano eruptions pushing the tectonic plates away from each other
Evidence: distribution of fossils from the same species are found in different continents, suggesting they were once joined occurence of the earthquake along the fitting coastline. Seismic wave produced by collision of 2 tectonic plates causing earthquake & tsunami

Genes, Chromosomes, and DNA

Gene: A small section of DNA that carries information determining our characteristics.
Chromosome: Carries all genetic information from parents.
DNA: Carries the instructions for the development, growth, reproduction, and functioning of all life.

Gametes

Sperm Cell (Male Gamete)
- Very small cells with tails for swimming movements.
Egg Cell (Female Gamete)
- Much bigger than a sperm cell because it contains food reserves.

Fertilization

The joining of the sperm cell with an egg cell.
The head of the sperm cell enters the egg cell.
The nucleus of the sperm cell & nucleus of the egg cell fuse together forming a new cell called a zygote.
Over the next few days, weeks, months, this single cell divides over and over again, eventually producing all of the million cells in a human body

Genetic Mutation

A change in the DNA sequence.
An example of genetic mutation is the pigmentation on cows. The spots on the cow helps them deter flies.