Thermal Energy

form of energy that flows from a region of higher temperature to a region of lower temeprature

Joule (J)

heat: 1) refers to the amt. of thermal energy being transferred from hotter to colder regions 2) SI unit is Joule (J) temperature: 1) refers to how hot or cold an object is 2) SI unit is Kelvin (K)

form of energy that flows from a region of higher temperature to a region of lower temperature

Joule (J)

heat: 1) refers to the amount of thermal energy being transferred from a hotter region to a colder region 2) SI unit: Joule (J) temperature: 1) refers to how hot or cold an object is 2) SI unit: Kelvin (K)

glass of test-tube gets heated first, causing it to expand and increase the volume of test-tube, leading to initial fall after a while, water in test-tube gains heat from ___, causing water to expand and since water expands more than glass, liquid level rises

glass of test-tube gets cooled first, causing it to contract and decrease the volume of test-tube, leading to initial rise after a while, water in test-tube loses heat from ___, causing water to contract and since water contracts more than glass, liquid level falls

magnitude of expansion: gases (largest), solids (least) intermolecular forces: solids (strongest), gases (weakest)

intermolecular forces is strongest in solids, followed by liquids then gases

when heated, volume increases, mass remains the same, density decreases when cooled, volume decreases, mass remains the same, density increases

volume of water decreases as temperature decreases towards 4°C volume starts to increase as temperature decreases from 4°C to 0°C volume is lowest at 4°C and hence, density is highest

allows aquatic life to survive during winter as the pond/lake does not freeze completely

concrete road: thermal expansion forces on very hot days will cause roads to crack provide expansion gaps railway tracks: can bend or twist due to expansion during hot weather provide sliding joints/expansion gaps bridges: can buckle under forces of expansion and contraction build rollers into it/provide expansion gaps electric cables and telephone wires: may become taut or snap when contracting in cold weather string them loosely from pole to pole laboratory glassware: when boiling water poured into thick glass, it might crack due to uneven expansion use pyrex (expands very little when heated) water pipes: unusually high pressures and leaks may occur when transporting hot water or steam build expansion loops or joints into them

1) fixing axel into wheels cool the axel for it to contract before fitting it into the wheel and allowing it to expand due to the forces of expansion, there is a very tight fit between the axel and wheel such that it will not come loose easily 2) hot riveting used to join smaller sheets of steel in ships, and shorter steel bars in cranes and bridges insert hot rivet through holes of 2 metal pieces which are to be fastened the other end of the rivet is hammered to form a new head when rivet cools, it contracts and pulls the metal pieces tightly together

formed by riveting or welding 2 different metals that expand at different rates together (e.g. brass and iron; brass expands more than iron)

conduction convection radiation

process of thermal energy transfer through a medium without any flow of the medium

materials that allow heat to flow through easily and have high thermal conductivity (e.g. silver, gold, copper)

materials that do not allow heat to flow through easily and have low thermal conductivity (e,g, wood, plastic, glass, vacuum)

heat is conducted away from the paper quickly by the metal and the paper around the metal rod never gets hot enough to burn

molecular vibration: 1) applies to all materials 2) slower process free electron diffusion: 1) applies only to materials with free electrons (e.g. metals) 2) faster process *free electron diffusion occurs in metals on top of molecular vibration and thus transfers heat easier

when heated, particles at heated end gain energy and vibrate faster and more vigorously they collide with neighbouring particles more often, passing some of their energy to them these neighbouring particles will vibrate faster and more vigorously and the energy is passed along to the next neighbouring particles, and subsequently the rest of the object