energy transfers by heating

• energy can be transferred from a hot object to a cold object by:

  • conduction
  • convection
  • radiation
• in conduction the particles vibrate faster so they collide with their neighbours more often which causes them to transfer some kinetic energy to those neighbouring particles.
• when an object is heated it expands because its atoms gain kinetic energy and move further apart.
• internal energy is stored by the particles (atoms and molecules) of a substance
• internal energy is the sum of the kinetic and potential energies of the particles in a system
• kinetic energy is due to the MOVEMENT of particles
• potential energy is due to the POSITION of the particles in the object, not the amount of matter in the object
• conduction is a method of energy transfer in SOLIDS
• a delocalised electron can leave the atom but not the metal - during conduction
• conduction is the transfer of energy by heating - between substances that are in DIRECT CONTACT with each other
• during conduction, a substance is heated and its particles gain MORE energy. causes them to vibrate more and collide with near-bye particles
• metals have delocalised electrons which are able to move around and transfer energy quicker.
• metals are good conductors because they allow energy to 'travel through them' easier.
• in conduction, when particles gain more energy and transfer it through vibrations - moving quicker and quicker.
• metals are good thermal conductors because they have a 'sea of delocalised electrons' that are free to move throughout the metallic structure
• non-metals are poor conductors of heat and electricity, they are brittle and have low melting and boiling points
• materials that are poor conductors of heat are known as insulators.
• graphite is a non-metal but it is a good thermal conductor because one of its outer electrons is free to move around.
• since metal is a great thermal conductor is has high thermal conductivity. when your body reaches contact with the metal, energy is transferred
• convection currents occur in liquids and gases where the particles, get heated and rise to the top where they soon cool down and sink back to the bottom
• infrared radiation is a type of electro-magnetic radiation that has similar properties to visible light but has a wavelength slightly longer that of visible red light
• all objects emit and absorb infra-red radiation, but the amount of radiation emitted depends on the temperature of the object
• an object hotter than its surroundings will emits more radiation EVERYY second than it absorbs, to cool down
• evaporation is when a liquid changes to a gas
• evaporation takes place from the SURFACE of the liquid at all temperatures
• boiling only takes place at a particular temperature because the particles are vibrating at a particular speed. this is called the boiling point and it occurs throughout the liquid
• increasing the surface area of a liquid affects the rate of evaporation (increases)
• increasing the temperature of a liquid affects the rate of evaporation (increases)
• increasing the movement of air across liquid affects the rate of evaporation (increases). for example, wet clothes dry faster in a breeze
• particles which have a higher kinetic energy are more energetic and 'break free' from the water becoming a gas. when the evaporation occurs, it causes cooling down in the liquid that has been left behind
• evaporation increases when more movement of air across the liquid's surface is created
• hot air always rises
• the insulator in a jumper are the wool fibres + air that is trapped between the fibres
• a good insulating material will trap lots of still air inside its structure so that less heat can be conducted away from your body