Conservation of energy Flashcards
What is the formula for change in gravitational potential energy?
ΔGPE = m x g x Δh
ΔGPE = Change in gravitational potential energy (J)
g = Gravitational field strength (N/kg)
Δh = Change in vertical height
What is the formula for Kinetic energy?
KE = 0.5 x m x v^2
KE = Kinetic energy (J)
v^2 = speed
What is conversation of Energy?
Energy can be stored, transferred between stores and dissipated - but it can never be created or destroyed. The total energy of a closed system has no net change.
A ball rolling up a slope
The ball does work against the gravitational force, so energy is transferred mechanically from the kinetic energy store of the ball to its gravitational potential energy store.
A bat hitting a ball
The bat has energy in its kinetic energy store. Some of this is transferred mechanically to the ball’s kinetic energy store. Some energy is also transferred mechanically to the thermal energy stores of the bat and the ball. The rest is carried away by sound.
A rock dropped from a cliff
Assuming there’s no air resistance, gravity does work on the rock, so the rock constantly accelerates towards the ground. Energy is transferred mechanically from the rock’s gravitational potential energy store to its kinetic energy store.
A car slowing down
Energy in the kinetic energy store of the car is transferred mechanically (due to friction between the tyres and road), and then by heating, to the thermal energy stores of the car and road.
A kettle boiling water
Energy is transferred electrically from the mains to the heating element of the kettle, and then by heating to the energy stores of the water/
Closed system
Where there are energy transfers in a closed system there is no net change to the total energy in that system.
When does a mechanical process become wasteful?
It becomes wasteful when they cause a rise in temperature so dissipating energy in that system.
