Chapter 1: Energy And Energy Resources Flashcards
How can energy be stored?
In a variety of different energy stores
What are the different ways energy is transferred?
It can be transferred via heating, waves, an electric current or by moving an object
What happens to an objects energy stores when it is dropped?
The object will gain speed when it is dropped, its store of GPE decreases and its store of kinetic energy increases
What happens when an object hits the ground?
Its kinetic energy store decreases, some or all of its energy is transferred to the surroundings, the thermal energy store of the surrounding increases, energy is also transferred by sound waves
Can energy be created or destroyed?
No
What is conservation of energy?
The conservation of energy says that energy cannot be created or destroyed
What is a closed system?
A closed system is a system in which no energy transfers take place out of or into the energy stores of the system.
Describe the movement of energy between energy stores
Energy can be transferred between energy stores within a closed system. The total energy of the system is always the same, before and after any transfers
When is work done on an object?
Work is done when a force makes the object move.
The energy transferred = Work done
Equation for work done with units
Work done (W)[joules] = force applied (F)[newtons] + distance moved(s)[meters]
How does work done affect friction?
Work done to overcome friction is transferred as energy to the thermal energy stores of the objects that rub together and the surroundings
Is work done equal to energy transferred
Yes
Energy transferred = the work done
How does the GPE of an object change when you move it up and down?
The GPE store of an object increases when it moves up
It decreases when it moves down
How is the GPE stores of an object affected when its lifted?
The GPE store of an object increases when it is lifted because work is done to overcome the gravitational force.
How is the GPE strength different on the moon than on earth
The GPE field strength at the surface of the moon is less that of earth
What is the equation for a change in an objects gravitational energy store?
Change in GPE energy store (joules)[J] = weight (newtons)[N] x change of height (meters)[m]
What does the kinetic store of a moving object depend on?
It depends on the objects mass and speed
How do you work out the kinetic energy store of an object (equation)?
Kinetic energy (joules)[J]= 1/2 x mass (kg) x speed squared (m/s squared)
What is the elastic potential energy?
It is the energy stored in an elastic object when work is done on the object
What is the equation for the elastic potential?
EPE (joules)[J] = 1/2 x spring constant (newtons per metre)[N/m] x extension squared (m squared)
What is useful energy?
Useful energy is energy in the place we want it and in the form we need it.
What is wasted energy?
It is the energy that is not useful and is transferred by an undesired pathway.
What happens to all wasted energy?
It is eventually transferred to the surroundings which become warmer
What happens when energy dissipates?
It gets less and less useful
What is the equation for efficiency?
Efficiency= useful energy output transferred (J)/ total energy supplied to the device (J) x100%
What is the maximum a devices useful energy transfer can be?
100%, no energy transfer can be more than 100% efficient.
How do machines waste energy?
Friction between moving parts, air resistance, electrical resistance and noise.
How can machines be made more efficient?
By reducing waste energy for example lubrication is used to reduce friction between moving parts.
What supplies most of the energy in a home?
Electricity and gas and/ or oil supply most of the energy in your home.
How should an electrical appliance be designed?
It is designed for a particular purpose and should waste as little energy as possible.
What is power?
It is the rate of transfer of energy
What is the power equation?
Power (watts,W) = energy transferred to appliance(E) [joules J]/ time taken for energy to be transferred(t) [ seconds,s]
P=E/t
What is the equation for the efficiency of an appliance?
Efficiency = useful power out/ total power in x100%
What is the equation for power wasted by an appliance?
Power wasted= total power input- useful power output
