Newton’s Laws

Forces

What is a force?

• a force is an interaction between two or more objects

• it may be attractive or repulsive

• it is a push, a pull or a twist

Four types of forces:

• gravity - all objects with a mass are attracted to one another. The bigger the mass, the greater the attraction

• electromagnetic - due to charged particles interacting

• weak force - a force inside a proton

• strong nuclear force - binds protons together in the nucleus

all other forces are just forms of these four

Important facts about forces

• they always come in pairs - every action has an equal opposite reaction (3rd Law)

• they can be balanced or unbalanced

• an object can continue moving without a force being applied to it - inertia (1st Law)

• forces act on an object, they are not a feature of the object

• there are both contact and non-contact forces

Contact and non-contact forces

Balanced and Unbalanced forces

• if forces in opposite directions are equal then they are balanced - there is no acceleration

• the object will stay still (if not moving) or will move with constant speed and direction

• if forces in opposite directions are not equal then they are unbalanced - there is acceleration

Newton’s First Law

an object will remain at rest, or remain in motion with constant speed and direction, unless acted on by an unbalanced force

this is often called inertia. inertia is the reluctance of an object to change. the greater the mass, the greater the inertia

Newton’s Second Law

If the resultant force is unbalanced, the object will move

How quickly it changes its speed is dependent on the force applied and the mass of the object

F=ma

This relates to inertia. The larger the mass, the more difficult it is to get the object to accelerate

The acceleration of an object is directly proportional to the force applied. The acceleration of an object is also inversely proportional to the mass of an object

Calculating acceleration

In reality, the acceleration of the object depends on the forces applied. You cannot apply an acceleration to get a force!

a = F/m

Newton’s 3rd Law

For every action there is an equal an opposite reaction

when body A exerts a force on object B, then object B will exert an equal force on A in the opposite direction

Remember: forces are interactions between bodies

Newton’s 3rd Law states that both bodies are always affected in an interaction

Whenever there is an action, there is always a reaction

F(ab) = -F(ba)

Key points

• forces always come in pairs. we call these ‘newtonian pairs’

• these forces act on different objects( each other). this is why they don’t cancel out

• forces are always of the same type, eg. pushing a box on the floor (contact) and the friction on the floor (contact)

• the forces are always equal in magnitude but opposite in direction

• they have different effects on the objects they are acting on because of Newton’s 2nd Law

Weight

We can take Newton’s 2nd Law and apply it to our weight

F(grav) = ma

when we calculate the force due to gravity, the acceleration is called ‘the acceleration due to gravity’ and is given the symbol ‘g’

F(grav) =mg

on earth, g=9.8m/s/s

Terminal Velocity

consider an object falling through a fluid such as air

at first, the object will accelerate due to the gravitational force (its weight)

as the object’s speed increases, the air resistance (reaction force) increases

after a time, the reaction force is equal to the weight. At this point the resultant force on the object becomes 0

Kinematics

What is speed?

• Speed is how fast an object moves. It is how much time it takes to cover a certain distance

• Speed is distance divided by time: speed = distance/time

What is kinematics?

Kinematics is the science of describing the motion of objects using words, diagrams, numbers, graphs and equations

Kinematics is a branch of mechanics

The goal of any study of kinematics is to develop sophisticated mental models that serve to describe (and ultimately, explain) the motion of real-world objects

Scalars vs Vectors

Distance and displacement

distance: total length of journey travelled

displacement: change in position, most direct route from start to finish

SI units: metres (m)

other units: kilometres (km) (needs to be converted to m)

Speed and Velocity

speed: how far an object travels in a given time interval

average speed: distance travelled along an object’s path divided by the time it takes to travel this distance

average speed = distance travelled / time elapsed

velocity: how far an object has been displaced in a given time interval

average velocity: displacement of an object divided by the time it takes to travel this distance

average velocity = displacement travelled / time elapsed

Velocity

velocity and speed are very closely related but they are not the same

velocity is the rate of change of displacement

(an object’s speed in a given direction)

v = s/t

where:

v = velocity (m/s)

s = displacement (m)

t = time (s)

Acceleration

• normally, accelerate just means ‘go faster’

• in physics, acceleration is the rate at which the speed or velocity of an object changes

a = (v-u)/t

v = final speed

u = initial speed

• acceleration is a vector so it has magnitude and direction

• the standard unit for acceleration is metres per second per second (m/s/s or m/s^2)

• deceleration is just negative acceleration

Acceleration could be:

• speeding up (increasing speed)

• starting to move from rest (increasing speed from 0)

• changing direction of linear motion eg. ball bouncing (changing speed from + to - or vice versa)

• slowing down - deceleration

• stopping - deceleration

• turning a corner (changing direction)

• circular motion (changing direction)

How do we accelerate?

1. speed up

2. slow down

3. change direction

Kinematics on the Road

Safety features in cars

car manufacturers are always introducing new safety features in cars such as

• seatbelts

• collapsible steering wheels

• padded dashboards

• head restraints

• airbags

• crumple zones

• ABS (anti-lock Braking System

regulators are also reducing the likelihood of major damage by reducing the speed limit in built up areas and mandating that cars have newer safety features

Headrests

inertia causes your head to keep moving in the direction it was before the crash. After the crash, the car bounces backwards and so does your head

without a properly configured headrest, your neck whips backwards - whiplash

Airbags

airbags protect you from hard things and to slow down your deceleration

when you hit a wall, or another car or big object, Newton’s 3rd law tells us the other object will push the car back with an equal and opposite force. Airbags slow down the rate of deceleration

DNA, Mutation and Genetic Technologies

DNA

What is a cell?

• the smallest unit of life

• all living things are made of cells

• most cells are too small to see with the naked eye

• cells contain organelles - small structures that perform specific functions and processes to keep cells alive

The nucleus

• an organelle that controls the cells activity

• the DNA is found in the nucleus

Chromosomes

• the chromosomes are very long strands of DNA, coiled up like a ball of string

• most human cells contain 46 chromosomes but sex cells only contain 23 chromosomes

DNA

• deoxyribonucleic acid is a molecule that contains genetic information

• DNA sequences must be converted into messages that can be used to produce proteins, which are the complex molecules that do most of the work in our bodies

Genes

• the DNA making up each chromosome is usually coiled up tightly. if we imagine it stretched out, it might look like beads on a string

  • each of these beads is called a gene

  • each gene is an instruction for a specific protein

  • thousands of genes make up each chromosome

All together…

the cell contains the nucleus, which holds the chromosomes, that contain tightly coiled strands of DNA, which are made of segments of genes that code for specific proteins that make up us

Genes found on DNA

• genes control the way a living thing looks, acts or works through the use of the proteins produced by those genes

• genes dictate a lot about how an organism looks and acts, but the environment plays a role as well

• genes are found in the nuclei of our cells, as specific lengths or segments of DNA

• our DNA makes us who we are, because it contains all of our genes

What is DNA?

• DNA is a polymer molecule, which means it is a very large molecule made up of small repeating units

• the repeating units in DNA are called nucleotides

• nucleotides come in pairs:

  • Adenine always pairs with Thymine

  • Guanine always pairs with Cytosine

• nucleotides are made of a sugar molecule, a phosphate molecule and a nitrogenous base (the A, T, G or C that makes it unique)

• once the nucleotides are all connected, the DNA takes on a shape called a double helix - like a ladder that has been twisted around itself

• the arrangements of As, Ts, Cs and Gs in a segment of DNA is what makes it a gene. A mechanism within the cell can read the code and turn it into a protein that will express the phenotype

History of DNA

• the discovery of the structure of DNA was credited in 1952 to James Watson and Francis Crick. They were awarded Nobel prizes for their discovery

• however, more recently it has been discovered that other scientists played important roles in the discovery of DNA’s structure, including Rosalind Franklin

The Genetic Code

• Mendel, an Austrian monk, understood and proved as far back as the mid 1800s that traits were passed down from parent to child

• our understanding of cell biology and genetics increased dramatically through the early 1900s, eventually leading to the structure of DNA in 1952

• for years following that discovery, scientists were still unsure of one major process - how do the genes encoded in our DNA become the proteins that give us our phenotype (observable trait)?

• this became known as the central dogma (a principle laid down by an authority as incontrovertibly true) in biology, and wasn’t fully resolved for decades

Proteins

• proteins are large, complex macromolecules made up of one or more long chains called polypeptides. polypeptides are made up of amino acids

• proteins perform the functions that help us live. they could be enzymes, structural, eg. muscles

Protein Synthesis

• DNA is a code which is read in groups of 3 nucleotides. Every group of 3 nucleotides in a gene codes for 1 amino acid. So, if a gene is 900 nucleotides long, it would produce a protein which is 300 amino acids long

• the DNA sequence of a gene must be read, and the code translated into a sequence of amino acids

• it’s as if your cells are translating from one language to another

The Process

• since the DNA instructions must remain in the nucleus, an intermediate molecule-messenger RNA (mRNA) is created; this carries a transcribed copy of the relevant instructions from the nucleus to the ribosomes in the cytoplasm

• the ribosomes can be considered as the ‘machinery’ that translates the message carried by the mRNA into a cell product such as protein

• RNA uses uracil (u) instead of thymine when creating RNA

DNA Replication

Mutation

• a mutation is a change in the genetic material of a cell

• the sequence of nucleotides (A, T, G and Cs) is altered

• can be spontaneous (through erroneous DNA replication) or induced (through mutagenesis)

• mutations can result in a change to the RNA created during transcription and the polypeptides/proteins created during translation

• mutations can be small (a single nucleotide) or large (whole chromosome) or anywhere in between

• effects of mutations can be positive, negative or neutral

Mutagens

• a mutagen is anything that has the potential to alter DNA in a living organism

• the process of inducing a mutation in a living organism is called mutagenesis and the resulting mutations are called induced mutations

• prior to the discovery of DNA (1952), mutagens were already being researched, as there were certain jobs/environments that lead more people to develop cancers (Eg people working with radiation and certain chemicals, people exposed to nuclear radiation/bombs)

• there are three types of mutagens: chemical, physical and biological

Advances in technology and our understanding of Biology

we have studied the structure of DNA and its role within living things. our knowledge and understanding of DNA has revolutionised biology, not just because we now know how the traits in living things are controlled, but also because we are learning how DNA can be used and even changed to suit our purposes as humans

DNA Profilling

• historically, people whose identities are unknown have been identified using fingerprinting. each individual has a different fingerprint, so if a fingerprint is found at a crime scene, it can be compared to existing databases of fingerprints to try and identify the owner

• recently, we have been able to create DNA profiles from tiny amounts of DNA to be used in much the same way as fingerprints. DNA profiles created with the same basic tools will be identical if they come from the same person, but different if they come from different people. people who are closely related will have DNA profiles with more similarities than unrelated individuals

• these profiles can now routinely be used to either identify potential suspects in criminal activities, potential parents where paternity is uncertain, and to establish evolutionary relationships between species

Genetically Modified Organisms

• the DNA of living organisms can be modified using a variety of techniques

• genes can be removed from the DNA of living organisms, or far more commonly, genes from other species can be cut, copy and pasted into the genomes of others

• one of the most common ways this technology is used is in adding the genes for specific vitamins to foods where these vitamins aren’t naturally found. one example of this is Golden Rice - a strain of rice that has the gene for beta-carotene added to it. the rice grows with a slight golden/orange colour to it, and provides those who eat it with beta-carotene that they wouldn’t normally have access to

• another incredibly useful application of GMO is the addition of the gene for insulin into bacteria - the bacteria will produce insulin which can be collected and used as medicine for people living with diabetes

Cloning

• cloning means making exact genetic copies of something - a gene, a tissue/organ, or an entire organism

• cloning can have many useful purposes - in the case of gene cloning, it can be used as a first step towards genetic modification, as making many copies of the gene of interest is important before it can be pasted into the genome of another organism. in the case of tissue/organ cloning, a genetically identical organ to transplant eliminates the risk off rejection and medical complications. in the case of whole organism cloning, a whole crop of identical plants can be grown quickly and easily. this is the case in most banana plantations in Queensland - all plants are genetic clones of each other

• whole organism cloning specifically can have some ethical implications

Radioactivity

Chemical reactions vs Nuclear reactions

Types of radiation

Radioactive materials

• most atoms are stable. however, radioactive atoms are not - they are unbalanced and unstable.

• they ‘want’ to become stable (balanced). so to try to achieve this state they emit energy in the form of radiation

• this releases energy. sometimes a massive amount of energy

Types of Radiation

• alpha decay

  • alpha - an atom decays into a new atom and emits an alpha particle (2 protons and 2 neutrons)

  • alpha radiation is the nucleus of a helium atom travelling at extremely high speed

  • the atomic number increases by a value of 1

• beta

  • beta - an atom decays into a new atom by changing a neutron into a proton and electron

  • the fast moving, high energy electron is called a beta particle

  • the atomic structure doesn’t fundamentally change

• gamma

  • gamma - after alpha or beta decay surplus energy is sometimes emitted. the atom itself is not changed

  • gamma radiation is part of the electromagnetic spectrum; a wave with a very high frequency, very short wavelength

Properties

• they travel different distances

• they have different strengths

• they are stopped by different materials

Isotopes and radioisotopes

What makes an atom unstable?

• isotopes occur when an atom has the same number of protons but a different number of neutrons

• when the number of neutrons is much greater than the number of protons, an atom becomes unstable

• we know that each element is composed of atoms which are the same as each other… but this is not entirely accurate

• within an element, all of the atoms have the same number of protons and the same number of electrons

• however, the number of neutrons within atoms of the same element can vary. these are called isotopes

• because all the protons are the same in each, they are all called the same name. but their mass numbers are different

Spontaneous decay

• spontaneous decay is the disintegration of an atom

• an unstable nucleus tries to reach a more stable nuclear configuration

• the process of radioactive decay occurs in general by three different methods

  1. a nucleus that changes one of its neutrons into a proton with the simultaneous emission of an electron - this is beta decay

  2. emitting a helium nucleus - this is alpha decay

  3. spontaneous fission, that is splitting into two fragments

• after decay, a resulting atom is often still radioactive

• this results in that atom decaying again - attempting to reach a stable state

• if often does this by emitting gamma rays

Half life

• radioactive decay is a random event

• for a given radioactive isotope, it’s impossible to predict when the nucleus will decay

• this is like throwing dice or tossing coins. we can’t pick the result of a single coin toss, but we know that over a large sample size we will get 50% heads and 50% tails

• the half life is the average time taken for half the nuclei in a sample to decay

• the shorter the half life, the faster the rate of decay

• nuclei have different degrees of stability, therefore they decay at different rates. the half life of an isotope is defined as the time required for half the initial number of radioactive nuclei to decay

• it is also the time required for the intensity of the radiation to halve

• each radioisotope has its own characteristic half life, which is unaffected by external conditions such as the composition of the compound it is found in, temperature and pressure

• half lives may be as short as a fraction of a second or as long as millions of years

Half life decay curves

• a decay curve shows how the number of nuclei of a radioactive element decreases with time

• after each half life, one half of the original radioactive nuclei have decayed into atoms of a new element

• note that the time for the material to halve its mass remains constant. after 5730 years, the mass of C has reduced to 5 g, after 11 450 years the mass has reduced to 2.5 and so on

Why is half life important

• we need to know the half life for a radioisotope when determining its suitability for a specific use

• for example, radioisotopes that are to be injected into the body should have relatively short half-lives. this will minimise the exposure of healthy tissue to damaging radiation

• technetium-99m and iodine-123 are used regularly in medical diagnosis and have half-lives of 6.0 and 13.3 hours respectively

Carbon cycle and dating

• all living things take in carbon-14 during their lifetime and this amount stays constant as new carbon-14 is taken in to replace the carbon-14 that decays

• when an organism dies, it no longer replaces the decayed carbon-14 which converts back to nitrogen-14 due to beta decay

• by measuring the amount of carbon-14 relative to carbon-12 in the sample, an estimate can be made of the number of half-lives have passed

Fusion and Fission

Generating energy with fission or fusion

• nuclear reactions cause a lot of energy to be released

• there are two methods to create energy

  • nuclear fission - a large nucleus is broken apart to form smaller daughter nuclei. in the process, energy is released. this is how nuclear power plants work

  • nuclear fusion - two smaller nuclei are fused together to form larger nuclei. energy is released as part of this process. this is what happens in stars such as our sun

Fission

• neutral neutron particles aren’t deflected as it approaches the nucleus

• neutral neutron fired at speed can force a large atom to split into smaller neutrons

• energy can be released from within certain nuclei

• if we can split the nuclei of heavy elements, the product will be approximately equal parts, with a release of neutrons and energy

• a uranium-235 nucleus will be split if a neutron hits it and is captured by the uranium nucleus

Chain reaction

• a self sustaining ‘chain reaction’ can be created - these are the reactions that drive nuclear reactions, and nuclear bombs

• only the U-235 undergoes fission and releases energy after it absorbs a neutron

• the products of fission are neutron and highly radioactive

• the three neutrons released can go on to hit other nearby U-235 nuclei, splitting them, and keeping the reaction going

• to maintain a sustained reaction for every 2 or 3 neutrons released, only one must be allowed to hit another uranium nucleus

• if this ratio is less than one, then the reaction will stop

Controlling a fission chain reaction

• a chain reaction process is a balanced system

  • neutrons are released in fission, to produce another fission in at least one additional nucleus

  • that nucleus in turn produces neutrons, splits further atoms and the process repeats

• chain reactions may be controlled - as in nuclear reactions, or uncontrolled - as in nuclear weapon detonation or a nuclear reaction meltdown

• because fission is initiated by neutron absorption, it is an example of an artificial transmutation

Fusion

• nuclear fusion is the merging of two nuclei to form a new atom with accompanying energy release

• another common fusion reaction is when two deuterium nuclei join together to form tritium - hydrogen-3 - and a proton

Nuclear reaction equations

Natural Radioactivity - alpha

• some elements decay naturally - by going under alpha, beta or gamma decay

• uranium-238 decays into thorium-234 and an alpha particle

• the atomic and mass numbers must balance on both sides of the equation

Natural Radioactivity - beta

• thorium-234 decays into protactinium-234 and a beta particle

• the atomic number increases by one during beta decay as a neutron decays into a proton, an electron and an antineutrino