Energy Changes Flashcards
State the law of energy conservation.
Energy cannot be created or destroyed
(it can only be transferred into different
forms).
Describe the energy changes involved when a ball is
thrown upwards and then returns to its starting
position. Ignore air resistance
● Upwards: KE is converted to GPE
● Peak: Maximum GPE, zero KE
● Downwards: GPE is converted to KE
KE (Kinetic Energy), GPE (Gravitational Potential Energy)
State any changes in the total energy of a ball that
is kicked, assuming that no external forces act.
The total energy of the system remains
constant due to the conservation of
energy.
Describe the energy changes that occur
in a filament light-bulb.
● Electrical energy is transferred into
light and heat energy
● Light is a useful energy form, heat is
waste energy
Describe the energy transfers for a bungee jumper.
● When falling, the GPE is converted to KE of
jumper
● As the cord tightens, KE is converted and
stored as Elastic Potential Energy (EPE)
● At lowest point, the jumper’s initial GPE
equals the EPE stored in the cord
Explain why a bungee jumper slows down once the
cord begins to stretch.
● Kinetic energy decreases since it is
converted to elastic potential energy
● Since KE is proportional to (velocity)², as KE decreases, so does velocity.
Describe the energy changes in a power station.
● Heat energy released in the reaction heats water to
make steam
● Steam moves the turbine, converting into kinetic energy
● Kinetic energy turns the generator
● Electrical energy as the generator generates
electricity
In what ways can the energy of a system be
changed?
● Through work done by forces
● Through electrical input
● Through heating
How can energy be changed through work done by
forces?
A force which moves an object (kinetic
energy) causes work to be done over a
distance.
What equation is used to measure the work done on
an object?
Work done (J) = force (N) x distance (m) W = Fd
Why do wasteful mechanical processes cause a rise
in the temperature of the surroundings?
They cause energy to be transferred by heating the surroundings.
What is the equation for kinetic energy? Give SI
units for all quantities involved.
E = ½ m v^2
Energy = ½ x Mass x (Velocity)²
Energy (J), Mass(kg), Velocity(m/s)
What is the equation for gravity potential energy?
Give SI units for all quantities involved.
E = mgh
Energy = Mass x Gravitational Field Strength x Height
Energy (J), Mass(kg), Gravitational Field Strength (N/kg),
Height (m)
