SPH3U Grade 11 Physics Energy and Heat Test

Physics Energy Unit Test Study Notes SPH3U

Outline

10 marks – comm.

10 marks – app.

40 marks – k/u – similar to textbook questions (short answer, *problem solving*, multiple choice)

Topic

Energy/Work – Eg, EK, W, EM, conservation of energy, efficiency, power

Heat/Thermal Energy

–          methods of heat transfer – conduction, convection, radiation

–          heat problems

–          latent heat

–          equilibrium

Need-to-know Terms

–          heat capacity

–          latent heat

–          power

–          energy

Energy/Work

Work (W)

–          energy transfer

–          done when a force is applied as an object is moved a certain distance

–          SI units for work is Joules (J)

–          Increases/lowers energy of an object by transferring energy

–          Work = Force X Distance

–          W = (F)(Δd)

–          Distance is always measured along the same line as the force that is being applied

Gravitational Potential Energy (Eg)

–          potential energy is energy stored in an object

–          potential energy can be released

–          gravitational potential energy is the energy that can be released by an object falling from a particular height

–          Eg = W = (F)(height)

–          Therefore, Eg = (m)(9.8)(h)

–          E.g. A ball weighing 2 kg is dropped from 50 m above the ground, what is its gravitational potential energy?

–          Eg = (2)(9.8)(50)

–          Eg = 980 J

Kinetic Energy (EK)

–          energy an object possesses as a result of its motion

–          objects travelling at higher velocities have more energy

–          more net force for a particular distance will result in higher velocity due to acceleration, meaning more kinetic energy

–          Ek = W = (m)(a)(Δd)

–          The above equation can be re-arranged to create: EK = (m)(V)2 / 2

Efficiency

–          cars are incredibly inefficient machines

–          all energy transformations result in some sort of energy lost to heat

–          efficiency of a device is the ratio of useful energy output to energy input (expressed as percentage)

–          Efficiency = (useful energy output / energy input)(100)

–          Efficiency = (EOUT / EIN)(100)

Mechanical Energy (EM)

–          simply the Eg + EK of an object

Conservation of Energy

–          energy never just disappears

–          energy is always transforming into different forms

–          e.g. a ball that is rolling slows to a stop because the kinetic energy is possessed was being transformed into heat energy due to friction

Power (P)

–          defined as the rate of change of doing work

–          it is the energy that is transferred, produced or used in a certain amount of time

–          power = work / time

–          P = ΔE / Δt

–          SI unit is the Watt (W), named after James Watt who invented the modern steam engine

–          1W = 1J / 1s

–          Horsepower is a non-metric unit sometimes used to measure power

–          1 hp = 746 W

Heat/Thermal Energy

–          thermal energy is the total kinetic energy and potential energy of the molecules or atoms within a substance measured in Joules (J)

–          temperature is the measure of the average kinetic energy of the molecules or atoms within a substance

–          temperature is measured in degrees Celsius or Kelvin

–          0K = -273.16 degrees Celsius

Equilibrium

–          two objects reaching the same temperature together

–          involves the heat capacity, mass, and initial temperature of the objects

Heat Transfer

–          symbol for heat is Q and units for heat are Joules (J)

–          heat is similar to work

–          can be transferred via conduction, convection, and radiation

Conduction

–          transfer of energy between molecules of one or more solids

–          occurs because of collisions between molecules

Convection

–          as a fluid (gas/liquid) becomes warm, the molecules become less dense and rise

–          molecules carry thermal energy, resulting in heat transfer

–          as fluid cools down, it begins to fall, creating a circular current

–          advection is hot fluids moving sideways rather than upwards

–          transfer of energy through electromagnetic waves like light, x-rays, ultraviolet radiation, infrared radiation, etc.

–          radiation can travel through space and does not require molecules

–          as radiation comes in contact with an object, it may or may not increase the object’s thermal energy

–          certain frequencies of microwaves can cause water to heat up significantly but have little to no effect on ceramic

–          infrared radiation is a part of the electromagnetic spectrum

–          invisible to human eye

–          molecules release thermal radiation over time

–          thermographs can create a picture of an object from the release of its infrared radiation

Calculating Heat

–          energy lost or gained by an object is proportional to mass and change in temperature of the substance

–          m is mass in kg, Q is heat, ΔT is the change in temperature = T2 – T1

–          c is a constant that’s called the specific heat capacity

–          Q = (m)(c)(ΔT)

Latent Heat

–          phase changes occurs when a substance changes state

–          solid to liquid (melting)

–          liquid to solid (freezing)

–          liquid to gas (evaporation

–          gas to liquid (condensation)

–          solid to gas (sublimation)

–          gas to solid (deposition)

–          during phase change, the temperature of the object does not change

–          the energy during a phase change goes towards breaking the bonds of molecules

–          energy is added/removed from substances

–          added energy works on bonds that keeps the substance in its current state

–          energy given off is the energy that was used to keep it in its current state

–          different substances require different amounts of energy

–          energy added/given off during phase change is called latent heat

–          latent heat fusion (Lf): energy that is required to turn a liquid to solid or given off when solid turns to liquid

–          Q = (m)(Lf)

–          latent heat of vaporization (LV): energy that is required to turn a liquid into gas or given off when gas turns to liquid

–          Q = (m)(LV)

Energy Resources

–          energy source – raw material that can be used to create work (e.g. fuels, solar power, etc.)

–          renewable – regenerates in a human lifetime

Active Solar

–          process of absorbing the sun’s energy and converting it into other forms of energy, such as electricity

–          radiant energy from the sun

–          produces small amounts of electrical energy

–          renewable source of energy

–          expensive to set up

–          only available when the sun is out

Passive Solar

–          process of designing and building a structure to take best advantage of the sun’s energy at all times of the year

–          renewable

–          expensive to set up

–          only available when sun is out

Hydraulic

–          energy produced by extracting potential energy from the water – gains potential energy from gravity, due to precipitation

–          renewable

–          only available where water flows regularly

Wind

–          energy produced by utilizing the kinetic energy of wind

–          readily available where wind is

–          does not create pollution

–          only available where wind is

–          available throughout Canada and across the world

–          not practical to install a wind turbine for a single home

–          usually costs more to get wind energy from suppliers

–          wind turbines are very loud and large

–          compared to other energy plants, wind energy plants tend to be easier to set up

Tidal

–          available where ocean tides are large

–          results from moon and sun

–          dams harness the energy of the moving water

–          doors are opened and closed to exploit the most energy out of the water

–          no air/thermal production

–          hard to produce electricity at certain times

–          dams effect ecology

Biomass

–          chemical potential energy in plant and animal waste

–          indirect result of sun, burning wood is an example

–          can be harnessed from many different sources

–          if not used correctly, could not be renewable

Geothermal

–          energy taken from underneath Earth’s surface

–          results from radioactive decay, the nuclear fission of elements in rocks

–          heated water gathers energy from below Earth’s crust

–          renewable but hard to harness

Nuclear Fusion

–          nuclei of atoms of light elements join together at high temperatures to create larger nuclei

–          as mass is lost, energy is created

–          resulted from sun and stars

–          limitless supply of fuel and less radioactive waste than nuclear fission

–          needs heat and confinement to work