Energy Flashcards
What is energy?
energy is the ability to do work
energy cannot be created or destroyed
energy can only be transferred from one store to another
What are the 8 stores of energy?
chemical kinetic gravitational potential elastic potential electrostatic/magnetic thermal nuclear
an accelerating car transfers energy from the…
chemical store of the cars fuel to the kinetic store of the car and the thermal store of the surroudings
energy can be transferred through pathways:
electrical
mechanical/work
heating (conduction and convection)
radiation (light and sound)
energy can be transferred into a useful store or
into an unwanted energy store. we say the energy has been dissipated (wasted)
dissipated energy usually refers to thermal energy of surroundings
Work done is the transferred energy when a force moves an object through a distance
what is the formula?
W=Fs
W means Work done/Joules (J)
F means force /Newtons (N)
s means distance moved in plane of force (m)
The driver of a car applies the brakes. The braking force is 1000N and it takes 20m to come to a halt.
How much work has been done?
What is the energy transfer?
W=Fs
W=1000 x 20
W=20000J
kinetic -> thermal
Gravitational store of energy formula
EG=mgh
EG means energy transferred to the gravitational store/Joules (J)
m means mass/kilograms (kg)
g means gravitational field strength/Newtons per kilogram (N/kg)
h means height/metres (m)
Kinetic energy store formula
EK=mv^2/2
EK means energy transferred to (or from) the kinetic store/Joules (J)
means mass/kilograms (kg)
v means velocity or speed/metres per second (m/s)
A 2kg ball with 24J of energy in its kinetic store travels at what velocity?
EK=mv^2/2
mv^2=2EK
v^2=2EK/m
v=4.9 m/s
Elastic potential energy formula
EE=ke^2/2
EE mean energy inthe elastic store/Joules (J)
k means the spring constant /Newtons per metre (N/m)
e means extension/ metres (m)
What is power?
power is the rate of doing work or the rate of energy transfer
power formula:
P=E/t
P means power/watts (W)
E means Energy/Joules (J) or Work done/Joules (J)
t means time/seconds (s)
Hooke’s law formula
F=ke
F means Force applied/Newtons (N)
k means spring constant/Newtons per metre (N/m)
e means extension/metres (m)
elastic deformation vs inelastic deformation
an object has been elastically deformed if it can go back to its original shape and length when the force is removed
an object has been inelastically deformed if it doesn’t return to its original shape and length when the force is removed.
