Topic 8 - Energy - forces doing their work Flashcards
(17 cards)
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)
What unit is 1 Watt equal to?
1 Joule per second (J/s)
What is the equation for efficiency?
Efficiency = useful output energy/total input energy
