conservation of energy & systems

• A SYSTEM:

  In physics, it's a portion of the physical universe, chosen to analyse & everything outside that system is the environment.

  
• The two types of systems:

  • Open system
  • Closed system

  
• OPEN SYSTEMS:


  The system can exchange matter or energy with its environment (all the matter that's outside of our system).

  • If you're making a cup of coffee & leave it, it COOLS down because the heat (energy) escapes – that's an open system.

  
• CLOSED SYSTEMS:


  • The system can't exchange matter or energy with its environment (all the matter that's outside of our system).
  • The total energy remains the same, even though energy can be transferred inside the system.

  
• CONSERVATION OF ENERGY:


  States that energy can be dissipated, stored or transferred usefully, but it can never be created or destroyed.
• The principle of CONSERVATION OF ENERGY:

  States that energy cannot be created or destroyed, only transferred between different ENERGY STORES.
• DISSIPATION of energy:


  Energy that's wasted or not usefully employed by a device.

  • not all energy transfers are useful.
• A beneficial transfer like when your phone rings & VIBRATES:

  • Energy moves from the CHEMICAL energy store of the battery, electrically to kinetic energy store of the phone's motor, causing it to vibrate.
  • But sometimes a phone gets WARM during use.
  • As energy is moving from the battery's chemical store, electrically to the THERMAL energy store of the phone itself.
  • This is NOT useful to the phone & wastes energy.

  This is an example of DISSIPATION of energy.

  
• To maximise efficiency & minimise costs, it's important to reduce unwanted energy transfers, especially the DISSIPATION of heat.

  • This is often seen in houses, where heat loss can lead to higher bills.
• To reduce unwanted losses, you can install following in your house:

  • cavity walls
  • loft insulation
  • double glazed windows
  • draught excluders
  • thick walls made of a material with low thermal conductivity
• THERMAL CONDUCTIVITY:


  A measure of how well a material conducts heat.

  • If a material has high thermal conductivity, it means heat can pass through it quickly.

  Metals have high thermal conductivity, feel cold to the touch; they are transferring heat away from your hand rapidly.
• CAVITY WALLS:


  Houses are constructed with two separate walls & an air gap between them.

  • reducing energy transfer by CONDUCTION as air has a LOW CONDUCTIVITY, but it allows convection.
  • So the gap is filled with INSULATION FOAM, which has lots of isolated air bubbles (which has an even lower conductivity) increases this effect even more.

  
• When it comes to buildings, the rate at which a building loses heat is influenced by:

  • the THICKNESS of the walls
  • their THERMAL CONDUCTIVITY
• • If walls are thin or made of materials with high thermal conductivity, the building will cool down quickly because heat escapes faster.
  • Thick walls with low thermal conductivity are better at keeping heat inside, which is why insulation is so important in homes.
• LOFT INSULATION (fibre glass):

  Fibre glass is a good insulator, it has a low thermal conductivity.

  • It reduces heat energy loss through both conduction & convection.
  • greater number of layers of insulation, the smaller the heat lost from roof.

  
• CONVECTION:


  Occurs when liquids & gases are able to MOVE and transfer heat.
• DOUBLE GLAZING WINDOWS:


  By having two layers of glass with trapped gas between them, these windows lessen energy loss due to CONDUCTION & CONVECTION, as air is a poor conductor of heat.

  • Single glazed windows only have one pane of glass.

  
• DRAUGHT EXCLUDERS:


  Placed around doors & windows, they're designed to prevent hot air from escaping, reducing CONVECTION losses.

  
• By minimising FRICTIONAL FORCES, you can reduce unwanted energy transfers.
• As you ride a bicycle, the chain moves over sprockets.

  • This movement causes FRICTION between the chain links & the sprockets.
  • Friction mechanically converts some of the KINETIC energy, which should be moving the bike forward, into THERMAL ENERGY.
  • That's wasted energy.
  • To combat this, LUBRICATE the chain with oil.
  • Lubrication reduces friction & allows for a smoother movement of the chain over the sprockets.
  • Meaning more of the kinetic energy is used to propel the bike forward, making your ride more EFFICIENT.

  
• It's B

  
• Energy is dissipated to the surroundings at the same rate that energy is transferred to the water.

  
• It's higher

  
• The tank is insulated. When the water is hot, the immersion heater switches off.

  • Compared to a tank with no insulation, the rate of energy transfer from the water in an insulated tank is lower.
  • This means that the water in the insulated tank stays hotter for longer.

  
• air bubbles are trapped in the foam and so the air cannot form convection current.

  
• The efficiency would increase because:

  • the amount of energy usefully transferred would increase
  • the amount of energy wasted would decrease

  Because less work is done against friction.

  
• • When plugging a phone into the wall to charge it.
  • Electrical energy from the main supply in the house travels along the wire.
  • It gets transferred to the chemical energy store in the phone’s battery.
  • When the phone is used, the chemical energy can be converted back to electrical energy.
  • This flows around the circuit in the phone & powers the different parts like the screen & the speaker
  • In the screen, the electrical energy will be converted to light energy, so that you can see it.
  • In the speaker, it will be converted to sound energy. 

  
• Waste energy is generally in the form of heat, which is why your phone might warm up a bit when it’s charging or when you’re using it a lot.

  
• As a bowl of hot porridge cools down, the energy in its thermal energy store is transferred to the surroundings.
• The main energy transfer of a marathon runner:

  Chemical energy ➔ kinetic energy

  • Some of the chemical energy from the runner's cells would also most likely be converted to thermal energy.
• A phone could be considered as a system & everything else in the universe would be the environment.

  • The phone would be an open system because energy & matter can freely move between the phone & the environment
  • If your phone gets hot, it gives out heat to the surroundings like your skin.

  
• If a phone is in a sealed jar, then the system would be the entire contents of the jar including the phone & the air within the jar.

  • it’s now a closed system, as energy or matter can’t enter or escape
  • When the phone heats up, the heat energy will be dissipated to the air inside the jar, so it stays within the system.
  • Meaning the overall energy of a closed system, doesn’t change.

  
• To keep houses warm, reduce the amount of heat energy that escapes to the outside environment like.

  
• You can reduce energy loss by:

  • Thermal insulation
  • lubrication
• Friction:


  The resistance that an object encounters when moving across a solid, or moving through a fluid.

  
• Friction reduces the efficiency of energy transfer & can cause objects to heat up.

  
• Lubricant helps to reduce friction between two surfaces.

  
• The friction between the cogs & chain of a bicycle makes it harder to pedal, but by adding oil (a type of lubricant) to reduce that friction & makes cycling easier.

  
• Fast moving vehicles like cars & planes have a streamlined shape to reduce friction from air resistance.

  • This allows them to use less fuel & more efficient.

  
• Double glazing costs £900 to install. It saves £50 a year in fuel costs.

  • It will take 18 years to recoup (make back) the initial costs.