P1 - Conservation And Dissipation Of Energy Flashcards
What are the energy stores?
Chemical energy
Kinetic energy
Gravitational potential energy
Elastic potential energy
Thermal energy
How can energy be transferred?
Heating
Waves
Electric current
Force moves an object
What is a flow diagram?
Shows the energy transfer
When an object falls how do energy stores change?
Gravitational potential energy
To
Kinetic energy
To
Thermal energy
When a pendulum swings how do energy stores change?
Maximum gravitational potential energy at far left and right and maximum kinetic energy at the bottom in the middle.
What is a system?
An object or a group of objects
Wyatcisvtye conservation of energy?
Energy cannot be created or destroyed, only transferred
What energy transferred happen to a bungee jumper after jumping of a platform?
Rope is slack energy is gravitational potential
Kinetic energy when they jump due to gravity
Role tightens and kinetic energy decreases and elastic potential energy increases.
Rope recoils and elastic potential decreases and kinetic store increases.
Some energy throughout is transferred to thermal store of surroundings by heating.
What is work?
When an object is moved by a force work is done on the object by the force so the force transfers energy to the object.
What is the equation for energy transferred?
Energy transferred = work done
How do you calculate the work done by a force when it causes displacement of an object?
Work done = force applied * distance moved
Joules = newtons * metres
How do you overcome friction?
Transferred to thermal energy stores by heating if you rub your hands together.
What is the force needed ti life an object at a constant velocity equal and opposite to?
Gravitational force on the object.
When does gravitational potential energy increase and decrease?
When an object is lifted y, gravitational potential energy increases. When the object is lowered down, energy decreases.
What is the equation for change in object’s gravitational potential energy store?
Change in gravitational potential energy store = weight * change of height
Joules = newtons * metres
What is another equation for change of gravitational potential energy store?
Change of gravitational potential energy store = mass * gravitational field strength * change of height
Joules = kilograms * N/kg * metres
What do results show about kinetic energy?
The greater the height dropped from, the faster the speed.
What happens to kinetic energy if speed increases?
Increases
What is speed dropped compared to kinetic energy?
Kinetic energy is directly proportional to the square of its speed
What store is used when you stretch something?
Elastic potential energy.
How do you calculate kinetic energy?
Kinetic energy = 1/2 * mass * speed squared
Joules = 1/2 * kg * m/s squared
How do you calculate elastic potential energy?
Elastic potential energy = 1/2 * spring constant * extension squared
Joules = 1/2 * N/m * meters squared
What is useful energy?
Energy transferred to where it is wanted in the way that is wanted
What is wasted energy?
The energy that is not usefully transferred.
What happens when energy is not transferred usefully?
It is dissipated and stored in less useful ways .
What happens with energy stores when you exercise?
As you exercise, energy is transferred by your muscles to the thermal energy store.
What happens to wasted energy?
It is dissipated to the surroundings
What happens the more energy spreads out?
It becomes less useful.
What is weight measured in?
Newtons.
What is energy measured in?
Joules
What is the input energy?
Energy supplied to a device .
What is useful output energy?
Useful energy transferred by the device
What is the rule of conservation of energy?
Energy cannot be created or destroyed only transferred.
What is the equation for input energy?
Useful output energy + energy wasted
What is the equation for efficiency?
Useful output energy transferred by the device / total input energy supplied to the device.
What do devices waste energy?
Friction between the moving parts causes heating
The resistance of a wire causes it to get hot when a current passes through.
Air resistance causes a force on a moving object that opposes its motion. Energy transferred from the object to the surroundings by this force is wasted.
Sound created by machinery causes energy transfer to the surroundings.
How do you reduce energy loss?
Lubricate the moving parts to reduce frictions
In circuits, use wires with as little electrical resistance as possible.
Streamline the shapes of moving objects to reduce air resistance.
Cut out noise bi tightening loose parts to reduce vibration
What is the useful energy and energy wasted in a light bulb?
Useful = light emitted from the glowing filament
Wasted = energy transferred from the filament heating the surroundings
What is the useful energy and energy wasted in an electric heater?
Useful = energy heating the surroundings
Wasted = light emitted from the glowing element.
What is the useful energy and energy wasted in an electric toaster?
Useful = energy heating bread
Wasted = energy heating the toaster case and the air around it
What is the useful energy and energy wasted in an electric kettle?
Useful = energy heating water
Wasted = energy heating the kettle itself
What is the useful energy and energy wasted in a hairdryer?
Useful = kinetic energy of the air driven by the fan, energy heating air flowing past the heater filament.
Wasted = sound of fan motor, energy heating The hairdryer itself
What is the useful energy and energy wasted in an electric motor?
Useful = kinetic energy of objects driven by the motor, gravitational potential energy of the objects lifted by the motor.
Wasted = energy heated by the motor and energy transferred by the sound waves generated by the motor.
What is power?
The energy you supply per second
How does power affect energy?
The more powerful an appliance is, the faster the rate at which it transfers energy.
What is power measured in?
Watts or kilowatts
What is the equation for power?
Power = energy transferred to the appliance / time taken for energy to be transferred.
Watts = joules / seconds
What is the equation for power wasted?
Power wasted = total power in - useful power out
What is the equation for efficiency?
Efficiency = useful power out / Toya power in all * 100
