Physics: Newton's Laws and Energy Concepts

Newton's Laws of Motion

• First Law (Inertia): An object at rest stays at rest and an object in motion stays in motion at a constant velocity unless acted upon by an unbalanced force.
  • Balanced Forces: Equal forces in opposite directions result in no motion or constant velocity.
  • Unbalanced Forces: Unequal forces in opposite directions produce an unbalanced force causing acceleration.
• Inertia: A property of an object that describes its resistance to changes in its motion. More mass means more inertia.
• Second Law: Force equals mass times acceleration (F = ma).
• Third Law: For every action, there is an equal and opposite reaction.
  • Example 1: When a gun is fired, the bullet moves forward, and the shooter is pushed backward with an equal force.
  • Example 2: When you step off a boat, the boat pushes back, often causing you to fall in.

Energy - Kinetic and Potential Gravitational

• Kinetic Energy: The energy of motion. Anything moving has kinetic energy.
  • Greater mass and speed = greater kinetic energy.
  • Equation: KE = 0.5mv^2
• Gravitational Potential Energy (GPE): A type of stored energy associated with objects above the ground.
  • On Earth, we always have the force of gravity acting upon us.
  • When we're above the Earth's surface, we have GPE, potential (stored) energy.
  • Depends on mass and height above the ground.
  • Equation: PE = mgh

The Law of Conservation of Energy

• Energy cannot be destroyed or created, only transferred or transformed from one form to another.
• PE = KE (potential energy can be transformed into kinetic energy)

Evolution - Natural Selection

• Process: An environmental factor impacts populations.
  • Selective agent: Selects the characteristic that will survive.
• Results: More or less offspring from particular organisms.
• Outcome: Organisms best suited to the environment survive and pass on their genes (survival of the fittest). Less adapted organisms produce less or not at all.
• Selective Agent: Can be a color of fur, trait, mutation, adaptation.
• Speciation: The process by which one species splits into two separate species.
  • Three Steps:
    • Variation
    • Isolation
    • Selection

Variation

• Natural selection depends on varying traits within a population.
• Genetic variation is caused by:
  • Mutation
  • Random mating/fertilization
  • Crossing over in meiosis
• Variation provides options for the species when an environment changes.
• Individual organisms may be wiped out.
• Favourable adaptations survive and continue the species' gene pool.

Isolation/Selection

• When two populations of a species are separated, gene flow is stopped.
• Two species with different selection pressures become more different.
• Eventually, they may become incapable of interbreeding, becoming different species.

Reproductive Isolation

• Species might not be able to breed due to:
  • Courtship behavior - new breeding rituals
  • Breeding seasons - breed at different times of year
  • Sterility - breed sterile offspring

Evolution

• Evolution is often accepted because of the law of natural selection.
• Natural Selection is a mechanism of evolution.
• It is the clearest explanation for the diversity of organisms.
• Mutation causes variation.
  • E.g. Sickle cell recessive alleles being passed on.
• Artificial selection is used for breeding.
  • Producing desired characteristics in specific offspring.
  • A faster form of evolution.

Evidence of Evolution

• Fossil Record
• Comparative Anatomy
• Comparative DNA and protein structure
• Geographical Distribution

Fossils

• Remains or traces of organisms from a past geological age embedded in rocks or other substances by natural processes.
  • Examples: footprints, imprints, faeces
• Helps provide evidence by showing an increasing number of species on Earth.
• Supports evolution because it shows that biodiversity increases if species continually split into two or more species overtime.
• Shows an increase in the complexity of species has changed over geological time.

Comparative Anatomy

• Compares structures of living species and fossils.
• Homologous structures: Structures with no apparent function and seem to reside from a past ancestor.
• Comparative embryology: Comparisons of vertebrate embryos show similarities in the early stages of development.
  • Vertebrate embryos have structures that appear to be homologous on the basis of anatomy.
  • The same gene has been produced, but with different effects in two different species.

Comparative DNA

• All living cells have some basic DNA structure and use some genetic code.
• Even though organisms seem very different, they have large sections of identical DNA.
  • Protein structure: Closely related species have more similarities in amino acid sequences in particular proteins.

Comparative Distribution

• A map of all the places where a species occurs.
• Many unique species live on isolated islands.
  • Less connection = less gene flow.
• With evolution, you would expect to find unusual species on particular islands because isolation helps speciation to occur.
• Continents now separated by oceans contain identical fossil species as they were once connected in the past.

Extra Notes

• Weight = Mass x Gravity
• Speed Conversions: 1 km/h = 0.2778 m/s and 1 m/s = 3.6 km/h

Example of Natural Selection: Peppered Moths

• Peppered moths show natural selection through color variation: some are light with black speckles, while others are entirely black.
• Before the Industrial Revolution, both types lived in rural and urban England.
• During the Revolution, pollution darkened city buildings with soot.
• Light-colored moths became easy prey for birds, while black moths blended in, survived, and reproduced.
• Over time, the black variant became more common in industrial areas.

Example of Natural Selection: Sickle Cell Anemia in Humans

• Sickle cell anemia, caused by a gene mutation, affects red blood cells' shape and oxygen-carrying ability.
• People with one sickle-cell allele (heterozygotes) are resistant to malaria, giving them a survival advantage in malaria-prone regions, where they pass on the allele to future generations.

Artificial Selection

• Darwin noted that farmers selectively bred animals for desirable traits.
• Unlike natural selection, which is driven by the environment and occurs slowly over generations, artificial selection is controlled by humans and can happen more quickly.
• Humans have bred plants and animals for thousands of years for traits like milk production, wool thickness, or meat yield.
• Belgian Blue cattle are bred for higher meat production.

Vestigial Structures

• Non-functional features fully developed and functioning in earlier species but serve little or no present purpose for an organism.
• Examples: Human appendix or tonsils.

Difference between Homologous and Vestigial Structures

• Homologous structures: Structures amongst two species that appear similar because they were developed from a common ancestor. For example, a human limb and whale fin are homologous because the bones have the same general layout.
• Vestigial structures: Features that appear in a species but no longer serve a function. They are traits that our ancestors needed, but no longer serve a purpose in our environment.

Analogous Structures

• Structures that serve a similar function but do not share an ancestor.

Selection Pressures

• An evolutionary force that causes a particular phenotype to be more favorable in certain environmental conditions.
• Selection pressures are considered forces that drive evolution via natural selection.
• Some phenotypes are more favorable than others, depending on external conditions.
• Selection pressures are external agents that affect an organism's ability to survive in a given environment.