SPH3U - Unit 3 - Energy and Society

Work Done

• Work - When a force is applied to an object, so it moves a certain distance

  • Measured in Joules or Newton metres, and is a scalar

  • W = F∆d cosθ

    • If F and d are in the same direction, θ = 0, so cosθ = 1

    • At 90 degrees, there is zero work

    • Greater than 90 degrees, there is negative work (the work is against the object’s motion)

• The area of a Force/distance graph is work

• Net work is a sum of all the work, considering both positive and negative work

• If a force is applied for a certain distance, but the object continues to move after the force has stopped, only use the distance that applies to the force

Energy

• Energy - The ability to cause a change or to do work

  • Mechanical Energy - The energy an object has due to its motion or position

  • Kinetic Energy - The energy of motion, which increases as speed increases

  • Potential Energy - The stored energy of an object due to its position or condition

    • Gravitational Potential Energy - The potential energy that increases when an object’s height increases

    • Elastic Potential Energy - Type of potential energy that increases when an object is stretched

  • Thermal Energy - Energy that increases as temperature increases due to faster moving particles

  • Electromagnetic Energy - Energy that travels in waves, such as light or x-rays which does not need to travel through matter

  • Sound energy - Energy that is carried by vibrations in matter

  • Electrical Energy - Energy carried by an electrical current

  • Chemical Energy - Energy in food and fuel, where chemical bonds are broken down to release energy

  • Nuclear Energy - Energy that is released when an atom is split in half or fused together

  • Sun - The main source of earth’s energy

Kinetic Energy

• Kinetic Energy - energy due to an object’s motion

• Depends on speed and mass, but speed has a bigger impact

• E_k = ½ mv²

  • Mass is in kilograms, speed is in metres per second, and energy is in Joules

• Work-Energy Principle - The net amount of mechanical work done on an object equals the object’s change in kinetic energy

  • W_net = ∆E_k

Gravitational Potential Energy

• Gravitational Potential Energy - Energy an object has due to its place and presence of a gravitational field

  • Depends on strength of gravity, vertical position from a reference point, and mass

  • E_g = mg∆h

    • Height is metres, mass is kilograms, and gravity is m/s²

Conservation of Energy

• Energy can convert into another type of energy

  • The total amount of energy will not change, but the individual types of energy may increase or decrease

• Law of Conservation of Energy - The total amount of energy in the universe is conserved. There is a certain total amount of energy, and this total never changes. New energy cannot be created out of nothing, and existing energy cannot disappear. The energy that exists can only be changers from one form to another.

Efficiency

• Energy does not go away, but its usefulness can be dissipated into wasted energy

• Efficiency - A measure of the amount of useful energy compared to the total energy

  • Efficiency = (E out)/(E in) x 100%

Different Types of Energy

• Renewable Energy - A substance with an unlimited supply or a supply that can be replenished as the substance is used in the energy-transforming processes

• Non-Renewable Energy - A substance that cannot be replenished as it is used

Power

• Power - The rate at which energy is transferred OR the rate at which work is done

  • P = W/∆t = E/∆t

    • E/W is measured in Joules

    • t is measured in seconds

    • Power is measured in Watts

Temperature

• Kinetic Molecular Theory - The theory that describes the motion of molecules or atoms in a substance in terms of kinetic energy

  • Everything is made of particles

  • Particles move

    • Vibrate in place for solids, fills container for liquids, and gas has no fixed shape or volume

  • Forces of attraction are between particles

  • Temperature is the average kinetic energy of the particles

    • Celsius - Defined by the melting point of ice and boiling point of water

    • Kelvin - The theoretical scale based on the motion of particles, where 0 is no kinetic energy

    • To convert: K -273 = C

Heat

• Thermal Energy - The total amount of kinetic and potential energy of the particles in an object

• Heat - The transfer of heat energy OR the flow of thermal energy from one place to another

• Heat can transfer by:

  • Conduction - A method of heat transfer within an object or between two objects in contact

    • Particles at a higher temperature collide with particles at a lower temperature

    • In the collision, energy is transferred so the slow particles speed up

    • This continues until equilibrium

    • Conduction works best for solids

  • Convection - The transfer of energy by the movement of higher energy particles to an area of lower energy

    • Heat causes expansion, which creates less dense matter

    • Hot matter rises, and cool matter sinks to take its place

    • The movement of the particles forms a convection current

    • Works best in liquids and gases

  • Radiation - The transfer of heat through infrared (electromagnetic) waves

    • All waves travel at the same speed, and do not need matter

    • The wavelength and frequency may differ

• Thermal Conductor - Materials that allow heat to flow through them more easily

• Thermal Insulator - Materials that do not allow heat to flow easily

Heat Capacity

• Specific Heat Capacity - The amount of heat lost or gained by a kg of a substance, so its temperature changes by one degree Celsius

  • ex. c of water = 4200J/kg∘C

  • Q = mc∆T

    • Q is the thermal energy released/absorbed

• Homeostasis - Maintenance of a temperature in a living system

• Principle of Thermal Energy Exchange - When thermal energy is transferred from a warmer object to a colder object, the amount of thermal energy released by the warmer object is equal to the amount of thermal energy absorbed by the colder object

  • Q(gained) = -Q(lost)

• When given a temperature change, plug in the given numbers, including ∆T

• When given an object placed into a substance of different temperature

  • Use the equation Q(gained) = -Q(lost)

    • gained is the object that was once cooler becoming warmer

  • Substitute Q = mc∆T into each equation

  • If solving for the final temperature, ∆T = T_f - T_i

Changes of State

• Phase - A physically distinctive form of matter

  • Solid - A substance with a definitive volume and shape, where the particles do not move freely

  • Liquid - A substance where particles are close together, but not fixed, and a definitive volume

  • Gas - A substance without a definitive volume or shape, containing the most kinetic energy

• Types of changes

  • Melting - Solid → liquid

  • Freezing - Liquid → solid

  • Boiling - Liquid → gas (throughout)

  • Evaporation - Liquid → gas (at surface)

  • Condensation - Gas → liquid

  • Sublimation - Solid → gas

  • Deposition - Gas → solid

• When substances lose energy, the temperature OR the state changes (not both simultaneously)

  • During a change of state, energy is released or absorbed, but not detected by a thermometer

  • Thermal energy goes in and particles gain potential energy

  • Heat is added, but the potential energy increases, not the kinetic energy

    • This is called latent heat

    • Latent Heat - The total thermal energy absorbed or released when a substance changes state

      • Q = mL

        • Mass is in kg

        • Latent heat is Joules/kg

      • Latent Heat of Fusion - The amount of thermal energy required to change a solid into a liquid or vice versa

      • Laten Heat of Vaporization - The amount of thermal energy required to change a liquid to a gas or vice versa

      • Specific Latent Heat - The amount of thermal energy required for 1kg to change from one state to another

• Vaporization - The process by which a liquid or solid changes to gas

• Boiling Point - The specific temperature at which a liquid is warmed to a high enough temperature

  • The greater the air pressure, the higher the boiling point

• To find the total energy of something that changes states and temperature, find each one individually, and then add

History of the Atom

• Democritus - matter is made of things called particles

• J.J. Thompson - Plum pudding model (discovered electron)

• Rutherford - Shot alpha particles at gold foil, and some bounced back

• Bohr-Rutherford Atom

  • Nearly all of the mass of an atom is concentrated in a very small, positively charged nucleus

  • The electrons travel around the nucleus

  • The orbits of the electrons correspond to a specific amount of energy

  • The nucleus consists of positive protons and neutral neutrons

Atoms and Isotopes

• Proton Number - How many protons in the nucleus, which identifies the element

• Mass Number - The total mass of protons and neutrons

• Atomic Mass - The average mass of isotopes (mass of the protons, neutrons, and electrons)

• Isotopes - Atoms with the same number of protons, but different mass numbers

  • Isotope notation:

    • The mass number goes above, the proton number goes below, and the element symbol goes beside

  • Radioisotope - An isotope that is not stable and will emit ionising radiation

• Number of protons = number of electrons

Radioactive Decay

• Radioactive Decay - The process where an unstable nucleus becomes more stable by emitting ionising radiation

  • Alpha Decay - An alpha particle (He-4) with a proton number of 2 is ejected

    • Alpha particles can not travel far

  • Beta Decay - A beta particle is emitted from the nucleus

    • An electron or positron is not found in the orbital

    • Electrons have a mass number of 0 and a proton number of -1

    • Positrons have a mass number of 0 and a proton number of +1

    • Particles can be a hazard if ingested

    • Particles travel farther than alpha

  • Gamma Decay - Gamma rays, which are very high energy electromagnetic waves

    • Travel very far

    • The gamma rays (γ) have a mass and proton number of 0

    • In gamma decay, a photon is ejected

Half-Life

• Radiation is probability

• Half-life - The amount of time for half of the radioactive material to decay, and the time for the amount of ionising radiation to decrease by one half

  • Not affected by external factors, so it can be reliable for carbon dating

  • Half-life is a recurring pattern, to that after the time of the half-life, half of the previous amount remains

• Use the equation A = A₀(1/2)^(t/h) to represent half-life, or graph

Nuclear Fission

• Law of Conservation of Energy - The total amount of mass and energy is constant

  • Mass can transform into energy, and energy into mass, such that the total mass-energy in an isolated system remains constant

  • E = mc²

    • Represents the amount of energy that can be created from matter

    • mass is kg

    • c is light speed (3 × 10^8)

• Atomic Mass Unit - 1/12 of a Carbon-12 atom, and 1.66 × 10^-27 kg

  • 1 proton = 1.007 u

• Mass Defect - In a nuclear reaction, it is the mass before - mass after = mass defect

  • The mass defect represents the amount of mass converted into the energy of that particular reaction

  • This, times the speed of light squared, is the binding energy

• Nuclear Fission - The decomposition of large, unstable nuclei into smaller, more stable nuclei

  • The binding energy of the nucleus is released when struck by a neutron, and other neutrons are struck loose, creating a chain reaction

  • Neutrons are too fast, so they must be slowed down with rods or heavy water

  • The heavy water also absorbs heat, turns into steam, and turns turbines to generate electricity

  • CANDU reactors use Uranium-235