# physics p1

?
• physics p1
• 1.1- changes in energy stores
• energy stores
• chemical- in fuels, food, batteries
• kinetic- stored by moving objects
• gravitational potential- stored in objects above the ground
• thermal energy- stored in objects with high temperature
• elastic potential- stored in springy objects when they're stretched or compressed
• energy transfers
• when an object is thrown into the air- energy transferred from kinetic energy store to grav potential energy store.
• when an object falls, it gets faster as energy is transferred from grav potential store to kinetic store.When it drops to the floor, energy is transferred to the thermal store and by sound waves to the surroundings.
• rollercoaster: as the rollercoaster inclines, the grav potential store increases When it descends, energy is transferred mostly to the kinetic energy store
• and partially to the thermal energy store of the surroundings by air resistance & friction and by sound waves to the surroundings
• bungee jumping; when rope is slack, energy transferred from gravy potential store to kinetic store, and when rope starts to stretch it is transferred to elastic potential store
• after jumper reaches bottom, rope bounces back up, transferring energy from elastic potential store to kinetic energy store until rope is slack, when energy is transferred from kinetic energy store to grav potential store
• rope never reaches original height as some energy  transferred to thermal energy store of surroundings
• 1.3- energy and work
• work done
• work is done on an object when a force makes it move, and so energy is transferred to it
• work done= force x distance
• friction
• work done to overcome friction is transferred to the thermal energy store
• 1.2-conservation of energy
• energy CANNOT be created or destroyed
• this applies to all energy stores and changes
• 1.4- gravitational potential
• gravitational potential energy= mass x gravitational field strength x height (gpe=mgh)
• when an object moves down, its gravitational potential decreases
• when an object moves up, gravitational potential increases
• it depends on:    .height     .weight
• 1.5- kinetic and elastic energy stores
• elastic potential
• elastic potential= 1/2 x spring constant x extenstin²
• ( e=1/2ke²)
• kinetic
• ke=1/2mv^2
• 1.6- energy dissipation
• useful energy is used for the purpose intended
• useful energy is eventually dissipated too
• the more it is further dissipated the more useless it is
• wasted is dissipated for an unintended purpose
• 1.7- energy and efficiency
• efficiency= useful output/ total input x100
• no energy transfer can be 100% efficient
• in machines friction can cause the parts to heat up, which wastes the energy
• this can be prevented with lubricant
• 1.8-electrical appliances
• electrical appliances transfer useful energy at the flick of a switch
• they should the smallest amt of waste energy possible, and are designed for a specific purpose
• 1.9- energy and power
• power is the rate of transfer of energy
• power= energy transferred/time taken  (pet)
• to work out power wasted,: total power in- total power out
• p2
• 2.1-conduction
• metals conduct better than non metals
• copper is a better conductor than steel
• glass conducts better than wool
• thermal conductivity
• the greater the thermal conductivity, the more energy transfer per second by conduction
• in insulators, the energy transfer per second depends on;
• the temperature difference across the material
• the thickness of material
• thermal conductivity of the material
• all objects emit and absorb infrared radiation
• hotter objects emit more
• a perfect black body is an object which absorbs all infrared radiation
• a good absorber is also a good emitter
• this is called black body radiation
• if an object emits radiation the same rate as it absorbs it, it has constant temperature.
• if it absorbs radiation faster than it emits it, its temperature increases.
• emergency blankets are shiny as they emit much less radiation than they absorb, which keeps the patient under the blanket warm.
• 2.4- specific heat capacity
• energy transferred= mass x specific heat capacity x temperature change
• you can rearrange this for shcapacity
• this is the amount of energy needed to heat 1kg of the substance by 1°c.
• the greater the mass of an object, the more time it takes to heat it up
• 2.5- heating and insulating buildings
• loft insulation- insulator like fibreglass laid on the loft.This is an insulator and it has spaces which reduce conduction+ thicker so more insulation
• cavity wall insulation- insulator is pumped into the cavity which is better than the air it replaces. It traps the air into small pockets, reducing conduction
• double glazed windows- vacuum between two glass panes = .thicker glass so less thermal conductivity .dry air is a good insulator so less conduction . no convection currents as its a vacuum