Energy stores and systems Flashcards
What is the formula for kinetic energy
1/2 x mass x v2
What is a system
A single or group of objects that your interested in
What is a closed system
Systems where neither matter nor energy can leave
How is heat energy stored
By heating an object you are transferring thermal energy into it
What is the energy transfer when chucking a ball
Chemical energy store in the arm transferred into a kinetic store into the ball
When a ball is dropped what is the energy transfer
Gravitational energy store becomes a kinetic energy store
Energy transfer when a car breaks
Kinetic energy from the breaking of the car to thermal energy from the tires which dissipates into the surroundings
Elastic potential energy store
Stretching or squashing an object can transfer energy to it’s elastic potential store
What is the conservation of energy prinicple
Energy can never be created or destroyed but can be transferred from one system to another
What is the equation for power
Power= energy / time
Or
Power= work/time
Define power
Either the rate of energy transfer or the rate of work done
What is conduction
The process of vibrating particles transferring energy to neighbouring particles
How is energy transferred by conduction
Particles in the object which are being heated collide with each other . These collisions cause cause energy to be transferred between partcilez
What is thermal conductivity
Measure of how quickly energy is transferred through a material in conduction
What is convection
Energetic particles move away from hot regions too cooler regions
Convection occurs in liquid and gases because …
Their particles are allowed to move around . When you heat these particles the vibrations cause further distance between them.
Insulation examples
Cavity walls- a gap between inner and outer walls . The air gap in the middle reduces the amount of energy transferred by conduction through the walls
Double glazer windows- gap between to widow panes . The air gap reduces heat loss
Thermal insulator PRACTICAL
Boil water in kettle . Pour water into a container measuring the volume of water
Use a thermometer to measure it’s initial temp
Seal the container for 5 minutes . Use a stopwatch
Remove the lid measure final temperature
Repeat experiment but use different materials . Testing how effective they are as insulators .
The lower the temperature difference the better the insulator
Efficiency equations
Either
Useful power output/ total power input
Or
Useful output energy transfer / total input energy transfer
Equation for work done
Force x distance
Joules
Kinetic energy
1/2 x mass x velocity2
Joules
Gravitational potential energy
Mass x gravity x height
Or
Weight x height
Power
Energy/time
WATTS
efficiency
Useful energy out / total input
The rate of energy transfer from a house can be reduced by …
Having walls with a low conductivity.
What unit is the joule equivalent to
NM
True or false ? If somethings moving there must be an overall resultant force
False
