ENERGY: FORMS,
TRANSFERS,
TRANSFERS, AND
AND
CONSERVATION
CONSERVATION
ENERGY: FORMS,
What is energy?
Different stores
Kinetic Energy (K.E.): Energy due to motion.
Gravitational Potential Energy (G.P.E.): Energy stored in an object
due to its position in a gravitational field.
Chemical Energy: Energy stored in the bonds of chemical
substances.
Elastic (Strain) Energy: Energy stored in an elastic material when it
is stretched, compressed, or deformed.
Other stores
Nuclear Energy: Energy stored within the nucleus of an atom.
Electrostatic Energy: Energy stored by charges due to their
position in an electric field.
Internal (Thermal) Energy: The total kinetic and potential energy of
the particles (atoms and molecules) within a substance. It is related
to the temperature of the substance.
How energy is tranferred between stores?
Energy is transferred from one store to
another during events and processes. It is
never "used up" or "lost," but often
dissipated as unwanted thermal energy.
By Forces (Mechanical Work Done):
Energy transferred when a force causes displacement.
Example: Pushing a trolley (chemical energy from
food in muscles
kinetic energy of trolley +
thermal energy due to friction).
Note: Work done = Energy transferred.
→
By Electrical Currents (Electrical Work Done):
Energy transferred by the movement of electric charges.
Example: An electric fan (electrical energy
kinetic energy
of blades + sound energy + thermal energy).
→
By Heating:
Transfer of thermal energy from a hotter region to a
colder region (conduction, convection, radiation).
Example: Boiling water in an electric kettle
(electrical energy
thermal energy of water).
→
By Electromagnetic Waves:
Energy transferred by waves such as light,
infrared, microwaves, radio waves.
Example: A solar panel (light energy
electrical energy).
Example: Cooking food in a microwave oven
(microwave energy
thermal energy in food).
→
→
By Sound Waves:
Energy transferred through vibrations.
Example: A loudspeaker (electrical energy
sound energy + thermal energy).
→
The principle of conservation of energy
Energy cannot be created nor destroyed, it can only be transferred from one
form to another or dissipated into the surroundings."
Application to Simple Examples with Energy Transformations:
Falling Object: A stone falling from a height.
G.P.E. at top → K.E. as it falls (some small amount transferred to
thermal/sound due to air resistance).
Swinging Pendulum:
Highest point: Maximum G.P.E., Minimum K.E.
Lowest point: Maximum K.E., Minimum G.P.E.
Throughout: G.P.E. ↔ K.E. (with some continuous dissipation to
thermal and sound due to air resistance and pivot friction).
Burning Candle:
Chemical energy (wax) → Light energy + Thermal energy.
Kinetic energy
Calculating the kinetic energy of a moving object.
Equation: KE​=mv^2/2
Where:
KE = Kinetic Energy (in Joules, J)
m = mass of the object (in kilograms, kg)
v = speed of the object (in meters per second, m/s)
Example: A car of mass 1200 kg is travelling at a speed of 20 m/s. Calculate
its kinetic energy.
Solution: KE=1200 kg×20^2
KE​=1200×200
KE=480000J
Gravitational potential energy
Calculating the change in gravitational potential energy when an
object's height changes.
Equation: ΔGPE​=mgΔh
Where:
ΔGPE = Change in Gravitational Potential Energy (in Joules, J)
m = mass of the object (in kilograms, kg)
g = gravitational field strength
Δh = change in vertical height (in meters, m)
A person of mass 60 kg climbs a flight of stairs, increasing their height
by 3 meters. Calculate the gain in their gravitational potential energy.
(Assume g=10 N/kg).
Sankey diagrams
Sankey diagrams are a visual way to represent energy transfers and show
how efficiently energy is converted from one form to another. The width of
the arrows is proportional to the amount of energy. They clearly distinguish
between useful energy output and wasted energy.
Split into 2 teams and answer the questions
1. A team of scientists test a brand new
hybrid car. They find out that 40% of the
energy is transferred as kinetic energy
(useful) and 55% is transferred as heat
energy (wasted).
a)How much energy is wasted as sound?
b)Draw a Sankey Diagram.
2. A team of scientists test a brand new
hybrid car. They find out that 40% of the
energy is transferred as kinetic energy
(useful) and 55% is transferred as heat
energy (wasted).
a)How much energy is wasted as sound
b)Draw a Sankey Diagram
Think about at least three different ways energy impacts
your daily life.
THANK YOU
THANK YOU