P1 Energy Flashcards
Energy
- The ability to do work
- Symbol E and measured in joules (J)
- Not something we can touch, but amount in a system can be calculated
System
- Group of interacting objects
- It’s a closed system if no energy is transferred in or out of the system
What are the 8 energy stores?
- Kinetic energy
- Elastic potential energy
- Gravitational potential energy
- Thermal energy
- Nuclear energy
- Electrostatic energy
- Magnetic energy
- Chemical energy
Law of conservation of energy
Energy is conserved -> never created or destroyed
Energy can be transferred from store to store -> some energy is wasted
What is work done?
- The energy transferred -> work done (W) = energy transferred (E)
- It’s measured in joules (J)
What are the 4 energy transfers?
- Mechanical work - Forces and waves e.g. sound
- Electrical work - electric currents
- Heating e.g. conduction and convection
- Electromagnetic radiation e.g. Light
Useful energy
The energy transferred to where it is wanted in the way it is wanted
Wasted energy
The energy that is not usefully transferred
Law of conservation of energy
Energy cannot be created or destroyed, only transferred between stores
Why does a bouncy ball not return to its starting height?
Because it is not a closed system. Energy is lost to:
- Air -> air resistance
- Floor -> heating
- The ball’s thermal energy store
What happens to wasted energy?
Dissipated to the surroundings
How to calculate work done
Work done = force (N) x distance (m)
Friction
A force that always opposes motion
Systematic error
Newton meter not set to zero at the start
Random error
Repeated measurements of the quantity give different results under the same conditions
Zero error
When the instrument gives a reading when the true reading at that time is zero
How to calculate gravitational potential energy?
Gravitational potential energy = mass x gravitational field strength x height
What is gravitational potential energy?
The work done against gravity to lift the object
How to calculate kinetic energy?
Kinetic energy = 1/2 x mass x velocity^2
What is kinetic energy?
The energy that an object possesses due to its motion
What is elastic energy?
The energy stored when we compress or extend something which will return to its original shape when we let it go
What is extension?
Extension is the change in length of an object: stretched length - original length
What is spring constant?
A measure of the stiffness of a spring
How to calculate elastic potential energy?
Elastic potential energy = 1/2 x Spring constant x extension^2
