Yr 9 - P1 - Conservation and dissipation of energy Flashcards
Kinetic energy
The energy stored in moving objects
Gravitational potential energy
The energy stored in objects raised above ground
Chemical Energy
The energy stored in
fuels, food and batteries
Thermal Energy
The energy stored by hot
objects
Elastic Potential
Energy
The energy stored by
stretched or squashed
objects
System change on a tennis ball being projected upwards?
Decreasing: Kinetic
Increasing: Gravitational
System change on a vehicle slowing down?
Decreasing: Kinetic
Increasing: Thermal
System change on a battery powered drill turning on?
Decreasing: Chemical
Increasing: Kinetic, Thermal
System change on a person sliding down on a zipwire?
Decreasing: Gravitational
Increasing: Kinetic, Thermal
What is the unit of work done and other forms of energy?
Joules (J)
Equation for work done?
Work done (J) = force(N) x distance(m)
W = F x s
Equation for energy?
Energy (J) = power (W) x time (s)
E= P x t
Equation for GPE?
GPE (J) = mass (kg) x gravitational field strength (N/kg) x height (m)
Ep = m x g x h
Equation for Kinetic Energy?
Kinetic Energy (J) = 1/2 x mass (kg) x speed² (m/s)
Ek = 1/2 x m x v²
Equation for Elastic Energy?
Elastic energy (J) = 1/2 x spring constant (N/m) x extension² (m)
Ee = 1/2 x k x e²
What is a system?
An object or group of objects
What is a closed system?
A system where no energy is added and none can escape (eg the universe)
Conservation of energy
In a closed system, energy cannot be created or destroyed. The total energy is constant.
What happens to energy in all systems?
Energy is dissipated so that it is stored in less useful ways (wasted energy)
Where does dissipated energy usually end up?
As a thermal store in the surroundings
How can unwanted energy transfers be reduced?
Lubrication (to reduce friction)
Insulations (to reduce the rate of thermal energy transfer
How is power defined?
As the rate of which energy is transferred or at the rate of which work is done
What is an energy transfer of 1 joule per second is equal to?
1 watt of power
2 motors lift the same mass but one of them has more power.
Which motor will lift the mass quickest?
The one with higher power
