Energy Flashcards
Kinetic energy
Stored in moving objects
Equation for kinetic energy
0.5 x mass (kg) x velocity² (m/s)
How do things move?
Chemical energy store in the thing ——> kinetic energy in movement
Gravitational potential energy
Stored in an object due to position above earth’s surface
Gravitational potential energy equation
Mass (kg) x gravitational field strength (N/kg) x height (m)
Elastic potential energy
Stored in stretched/ compressed objects
By putting energy into it by squeezing/ stretching it will store it as elastic potential energy
Elastic potential energy equation
0.5 x spring constant (N/kg) x extension² (m)
What is the spring constant of an object?
A measure of the ratio a force is applied to it and the extension caused by it
Extension in elastic objects
The extra bit in a spring caused when stretching it
Can extension in a spring be negative?
Yes if compressed
Internal energy
Total kinetic and potential energy in particles
Usually vibrations of solid particles
What happens if you increase the force applied on a spring?
It will extend
Directly proportional to the force applied
Hooke’s law
Force and extension are directly proportional
By being multiplied by a spring constant
Limit of proportionality
When a spring has been stretched beyond its limit
So when the force is removed it no longer returns back to its original position = no longer directly proportional
Energy transfer
When energy is transferred from one store to another
Also known as work being done
Law of conservation of energy
Energy can be transferred to another store, stored, or dissipated
but NEVER made or destroyed
System
An object/ group of objects
Closed system
When no energy can enter or leave so the total amount stays constant
Even after transfers
Energy transfers in a pendulum
At the furthest point on the side it has highest gpe
Swings down and transfers to kinetic energy
Repeats then eventually stops due to air resistance
Energy transfers in bungee jumper
Gpe store at highest point
Jumps, begins transferring to Ek
Maximum Ek
Rope tightens and all Ek ——> Ee due to extension caused by force. Stops moving
Rope recoils, Ee——> Ek
Moving upwards = back to Gpe
What is a result of friction on energy transfer?
Friction causes some energy transferred to thermal energy
So surrounding temperature increases
If this repeats the system may stop moving due to all transferred to thermal energy
How to stop unwanted energy transfer ?
Use lubricant = less rubbing and friction
Remove air particles around
Types of energy transfer
Mechanical (using force to move)
Electrical (voltage)
Heating
Radiation
Work done equation
Work done (J) = Force (N) x distance (m)
What can work be measured in?
J or N/m
Power
The rate at which energy is transferred/ work is done
High power object
Transfers energy fast
Low power
Transfers energy slow
What is power measured in?
Watt (W)
Power equation
Energy —-> /work done (J)
———————————————
Time (s)
Efficiency
The percent of energy we put in is transferred to useful store
Because some is transferred to unwanted stores
What can we use to calculate efficiency
Power
or
Energy transfer
Using power to calculate efficiency
Useful power output
——————————
Total power input
(x100)
Using energy transferred to calculate efficiency
Useful output energy transfer
——————————————
Total input energy transfer
(x100)
How to increase efficiency when heating water?
Use a lid = stop heat transfer up
Use insulating material to prevent transfer from sides
Put heat source inside the appliance like a kettle
Use large base so all energy transfer into the pan
Thermal conductivity
The rate of thermal energy transfer by conduction across a material
High thermal conductivity
Higher rate of energy transfer so object will cool faster
If trying to preserve energy = BAD
Low thermal conductivity
Slow rate of energy transfer so object stays warm faster
If trying to keep heat in = GOOD
Where can heat transfer through in a house?
Walls
Windows
Loft
How to insulate a wall
There’s usually a cavity heat can transfer through easily between exterior and interior wall
So use insulating material between = low thermal conductivity
How to insulate a window
Double glazed for low thermal conductivity
How to insulate a loft
Use loft insulation
Why do we want to decrease the heat transfer in homes?
So we can reduce energy costs
