Topic 8 - Energy - forces doing their work Flashcards
Describe the changes involved in the way energy is stored when systems change
Energy is never created or destroyed, it is only transferred. Therefore, when a system changes energy is transferred from one form to another.
What is a closed system?
A closed system is a system which experiences no external forces
What does/doesn’t happen when there are energy transfers in a closed system?
There is no net change to the total energy in that system
What are the three ways that the energy of a system can be changed?
-Through work done by forces
-In electrical equipment
-In heating
How does the energy of a system change when work is done by forces?
An external force transfers energy to a system
How does the energy of a system change in electrical equipment?
Chemical potential energy stored in batteries forms electrical energy
How does the energy of a system change in heating?
Electrical energy transfers to thermal energy. (Increased energy in the kinetic store of the particles) This either raises the system’s temperature or produces a change of state.
What does work done mean?
The work done by a force (Joule) is equal to the energy transferred (Joule)
What is the equation for work done?
E = F*d
work done (Joule) = force (Newton) x distance moved in the direction of the force (metre)
What is the equation for change in gravitational potential energy?
∆GPE = m⋅ g ⋅∆h
change in gravitation potential energy (Joule) = mass (kilogram) x gravitational field strength (Newton per kilogram) x change in vertical height (metre)
What is the equation to calculate the amount of energy associated with a moving object?
KE = ½mv²
Kinetic energy (Joule) = ½ x mass (kilogram) x speed² (metre/second²)
Explain how in all system changes energy is dissipated so that it is stored, etc…
Energy is rarely 100% transferred into the desired form. It dissipates/is wasted by being lost to the surroundings.
Explain that mechanical processes become wasteful when they cause a rise in temperature, etc…
Mechanical processes are wasteful when they get hot (usually due to friction). Energy is dissipated as heat, causing a rise in temperature so the energy is lost to the surroundings.
Define power
The rate at which energy is transferred.
What is the equation for power?
P = E/t
Power (Watt) = work done (Joule)/time taken (second)
