Physics – Key Topic 1
4.1 Energy
4.1.1 Energy changes in a system, and the ways energy is stored
before and after such changes
4.1.1.1 Energy stores and systems
Types of energy
- Kinetic energy – energy a moving object has
- GPE – energy an object has when its off the ground
- EPE = energy an object has when its stretched or compressed
- Sound energy – the energy an object has when it vibrates. It creates sound waves
- Nuclear energy – energy stored in the nucleus of an atom
- Light energy – radiated as light energy by waves
- Heat energy – form of energy that is transferred between systems or objects with
different temperatures
- Electrical energy – energy due to moving charges
- Chemical energy – energy stored in bonds between molecules and atoms
A system is an object or group of objects
There are changes in the way energy is stored when a system changes
Energy is needed to make objects move and to keep devices working
- most of the energy we use is obtained from burning fuels such as coal, oil and gas
- energy is stored in different forms and can be transferred to other stores
- newton’s law states that energy can not be created or destroyed – only dissipated.
Therefore it is transferred from one energy store to another
4.1.1.2 Changes in energy
The kinetic energy of a moving object can be calculated using the equation:
- Kinetic energy = 0.5 x mass x speed2
- Ek = 0.5mv2
, - M is mass in kg, v is speed in m/s
- Energy is transferred to this store when an object speeds up and is transferred
away from this store when an object slows down
The amount of elastic potential energy stored in a stretched spring can be calculated
using the equation:
- Elastic potential energy = 0.5 x spring constant x extension2
- E = 0.5ke2 (assuming the limit of proportionality has not been exceeded)
- K is spring constant in N/m and e is extension in m
- Hooke’s law = force(N) = spring constant (N/m) x extension (m)
- His law states that the extension of a spring is directly proportional to the force
applied as long as its limit of proportionality isn’t exceeded. Elastic limit is the
furthest point a material can be stretched or deformed while being able to return
to its original shape. Beyond the limit of proportionality is when the extension of a
spring is no longer proportional to the force applied to it
- More than one force must be applied to change the shape of a stationary object
by stretching, bending or compressing, because a single force would simply cause
the object to move in the direction in which the force were to be appleid
The amount of gravitational potential energy gained by an object raised above ground
level can be calculated using the equation:
- Gpe = mass x gfs x height
- E = mgh
- M is mass in kg, g is gravitational field strength in N/kg, h is height in m
Weight vs mass
Mass is a measure of the amount of material In an object, however weight is mass
multiplied by acceleration of gravity
Weight (N) = mass (kg) x gfs (10N/kg on earth)
4.1.1.3 Energy changes in a system
The amount of energy stored in or released from a system as its temperature changes
can be calculated using the equation:
- Change in thermal energy = mass x SHC x temperature change
- E = mct
4.1 Energy
4.1.1 Energy changes in a system, and the ways energy is stored
before and after such changes
4.1.1.1 Energy stores and systems
Types of energy
- Kinetic energy – energy a moving object has
- GPE – energy an object has when its off the ground
- EPE = energy an object has when its stretched or compressed
- Sound energy – the energy an object has when it vibrates. It creates sound waves
- Nuclear energy – energy stored in the nucleus of an atom
- Light energy – radiated as light energy by waves
- Heat energy – form of energy that is transferred between systems or objects with
different temperatures
- Electrical energy – energy due to moving charges
- Chemical energy – energy stored in bonds between molecules and atoms
A system is an object or group of objects
There are changes in the way energy is stored when a system changes
Energy is needed to make objects move and to keep devices working
- most of the energy we use is obtained from burning fuels such as coal, oil and gas
- energy is stored in different forms and can be transferred to other stores
- newton’s law states that energy can not be created or destroyed – only dissipated.
Therefore it is transferred from one energy store to another
4.1.1.2 Changes in energy
The kinetic energy of a moving object can be calculated using the equation:
- Kinetic energy = 0.5 x mass x speed2
- Ek = 0.5mv2
, - M is mass in kg, v is speed in m/s
- Energy is transferred to this store when an object speeds up and is transferred
away from this store when an object slows down
The amount of elastic potential energy stored in a stretched spring can be calculated
using the equation:
- Elastic potential energy = 0.5 x spring constant x extension2
- E = 0.5ke2 (assuming the limit of proportionality has not been exceeded)
- K is spring constant in N/m and e is extension in m
- Hooke’s law = force(N) = spring constant (N/m) x extension (m)
- His law states that the extension of a spring is directly proportional to the force
applied as long as its limit of proportionality isn’t exceeded. Elastic limit is the
furthest point a material can be stretched or deformed while being able to return
to its original shape. Beyond the limit of proportionality is when the extension of a
spring is no longer proportional to the force applied to it
- More than one force must be applied to change the shape of a stationary object
by stretching, bending or compressing, because a single force would simply cause
the object to move in the direction in which the force were to be appleid
The amount of gravitational potential energy gained by an object raised above ground
level can be calculated using the equation:
- Gpe = mass x gfs x height
- E = mgh
- M is mass in kg, g is gravitational field strength in N/kg, h is height in m
Weight vs mass
Mass is a measure of the amount of material In an object, however weight is mass
multiplied by acceleration of gravity
Weight (N) = mass (kg) x gfs (10N/kg on earth)
4.1.1.3 Energy changes in a system
The amount of energy stored in or released from a system as its temperature changes
can be calculated using the equation:
- Change in thermal energy = mass x SHC x temperature change
- E = mct
