Energy and Energy Resources Chp 1 Flashcards
The two principles of energy changes
1- Energy can be stored in a variety of different energy stores (Chemical energy, Gravitational potential energy in an object, thermal energy of temperature)
2- Energy is transferred by heating, by waves, by electric current or by a force when that force moves an object
What changes in energy occur when a ball falls in the air?
Gravitational potential energy is converted to kinetic energy as it speeds up. Air resistance causes some energy to be lost as heat.
(hold an object- gravity pulls it- drops it so it moves = kinetic)
What changes in energy occur when an electric heater is switched on?
Electrical energy is transformed into thermal energy.
What changes in energy occur when burning a candle in a powercut?
Chemical energy is stored in a candle as it is wax. Burning wax produces heat (thermal energy) then gives off light (light energy).
What changes in electricity occur as an electric train moves uphill?
Energy is transferred from electric energy to kinetic energy and gravitational potential energy, as it is moving (1) and uphill against gravity (2).
What changes in electricity occur as an electric train slows down and stops at a station?
Kinetic energy reduces as it reduces speed. The kinetic energy transforms as it slows down- friction on brakes releases some thermal energy.
What is friction and what does it do?
Friction is the force that opposes objects moving against each other. Friction releases heat energy.
When you drop an object, what energy is released in place of kinetic? (what happens when it stops moving/hits the ground?)
- A Noise = energy as sound waves
-Contact with the ground = friction = energy as heat
What is the law of conservation of energy?
That energy cannot be created or destroyed.
Why is conservation of energy so important?
It applies to all energy changes- the total energy before is the same as after, even in different forms. Some energy however, may be lost as ‘waste’.
What is a closed energy system?
A system in which no energy transfers take place out of or into the energy stores of the system. Like a pendulum.
What happens when a rope is stretched?
Its elastic potential energy increases as it becomes tight, its kinetic energy of the stretch decreases.
What changes in energy occur when a ball hits the floor and bounces?
Starts with high gravitational potential energy (GPE), then falls gaining kinetic and losing GPE. On bouncing, some kinetic energy turns to elastic energy as the ball squishes, when it reshapes it returns to kinetic. Some energy is lost on impact to sound and heat from friction, therefore the kinetic energy is less and it doesn’t bounce as high.
Compare the energy stores of a ball being held vs bouncing on the floor
Being held = High gravitational potential energy, low kinetic energy.
Upon bouncing = low gravitational, high kinetic energy, some energy lost as heat and sound
What do we call it when an object is moved by force?
Work done
What happens when work is done?
Energy is transferred by force. The amount of energy is equal to the ‘work done’ on it.
What is the equation for work done?
Work Done (Joules) = force applied (Newtons) x distance moved (Metres)
Also called W = F x S
What happens to work done to overcome friction (resistance to movement on contact)?
Energy is transferred to thermal energy stores.
What happens in terms of energy changes and work done when a rower rows a boat?
Energy Transfers: The rower converts chemical energy (from food) into kinetic energy (motion of the boat).
Energy Stores: Chemical energy in muscles → kinetic energy in the moving boat.
Work Done: The rower does work against resistance (water drag)
What happens to gravitational potential energy when an object is moved upwards?
The energy in its gravitational potential energy increases. The increase is equal to the work done by lifting.
What happens to the gravitational potential energy when an object moves down?
It’s gravitational potential energy store decreases equal to the work done by gravity to bring it closer to the floor.
Which 2 things do gravitational potential energy depend on when an object moves up or down?
How far it is moved vertically (change in height) and it’s weight.
How to calculate change in object’s gravitational energy potential store
Change in objects GPE store = weight (newtons) x change of height (metres)
What is the meaning of 𐤃Ep (J) = M (kg) x G (N/kg) x 𐤃h (m) ?
Change in gravitational potential energy store (joules) = mass (kg) x gravitational field strength (newtons/kg) x change in height (metres)
What is the kinetic energy equation? (to get Ek in joules)
Kinetic energy ek (joules) = 1/2 x mass (kg) x speed squared (metres per second)(squared)
What two things do kinetic energy stores depend on?
Mass and Speed
What does Hooke’s Law describe?
That force increases with the extension of a spring. This means to extend a spring further, it requires more force. The relationship is described as F = k e
What’s the full equation for Ec = 1/2 x k x e(squared)?
Elastic potential energy (joules) = 1/2 x spring constant (newtons/metre) x extension(squared) (metres)(squared)
