Energy transfer, work and power Flashcards
Work done is the same as
Energy transferred
Conservation of Energy
Energy cannot be created or destroyed, it can only be transferred from one store to another
Power definition
The rate of transfer of energy/doing work
Stopping distance of a vehicle =
Thinking Distance + Breaking Distance
Factors affecting thinking distance
Distractions
Alcohol
Drugs
Tiredness
Visibility
Age
(Speed)
Factors affecting breaking distance
Speed
Worn brakes
Wet/slippery road
Mass of car
Worn tyres
Icy road
Efficiency
Useful energy output/total energy output x 100%
Conduction
Through solids: Thermal energy is transferred through a material; heat is passed from particle to particle by vibrations and collisions
Why are metals good conductors
They have a sea of delocalised electrons which can collide with the atoms, helping to transfer the vibrations through the material and hence transfer heat better
Convection (currents)
Through liquids/gases: When a fluid is heated, the molecules expand and become less dense than the surroundings. The hot fluid rises, and the cooler surrounding fluid moves in to take its place. Eventually, the hot fluid cools and sinks back down and the process repeats.
Thermal Radiation
All bodies emit thermal radiation no matter what temperature
The hotter an object, the more infrared radiation it radiates in a given time
Radiation can travel in a vacuum (does not require particles)
Black objects absorb and emit radiation well
Shiny objects absorb and emit radiation very poorly (it reflects)
Insulation
Reduces energy transfers from both conduction and convection
The lower the thermal conductivity of the insulator, the less energy is transferred
The less dense the insulator, the less conduction can occur (particles further apart)
The thicker a material, the better it will insulate
