Topic 1 - Work, Energy and Power Flashcards
1What is a closed system
A system in which neither energy nor matter can enter or leave. Net change is always zero.
What happens when a system changes
Energy is transferred between different stores when work is done by a force or by a current flowing.
Baby Bouncer Question
The baby initially has GPE, when he moves down the GPE is mechanically converted into the baby’s KE and the spring’s EPE. At the end, all the energy is stored as EPE in the spring
Collision between car and wall
Energy transferred mechanically from KE of car to TE of car and wall. Some energy will also be transferred away as sound waves.
Conservation of Energy
Energy cannot be created or destroyed, only stored transferred usefully or dissipated.
Dissipated energy
Whenever there is a change in system, some of the energy transferred is dissipated. This is ‘wasted’ energy as it is not transferred to useful stores.
Kinetic energy
1/2 x mass x (velocity)^2
1/2mv^2
GPE
mass x gravitational field strength x height
mgh
EPE
1/2 x spring constant x extension^2 (m)
Specific Heat Capacity
How much energy it takes to heat 1kg of the material by 1 degree celsius.
ΔE = mcΔt
change in energy = mass x specific heat capacity x change in temp
power
energy transferred / time
How does conduction work
-When one part of an object is heated, its particles gain more kinetic energy.
- These particles vibrate more and collide with neighbouring particles, transferring kinetic energy to them.
- These collisions cause the kinetic energy to spread through the object’s particles, and by extension heat.
How can you keep your house warm in winter?
Thick walls with low thermal conductivity , as it reduces energy transferred away from the house due to its insulating properties
How does lubrication reduce the amount of energy dissipated
Lubricating reduces work done against friction between objects’ surfaces.
This reduces the amount of energy dissipated as thermal energy of surroundings
This increases the efficiency.
efficiency
useful energy output/ total energy input
