Topic 3: Conservation of Energy Flashcards
formula for gravitational potential energy
change in gravitational potential energy (J) = mass (Kg) x gravity (N/Kg) x height (m)
formula for kinetic energy
1/2 x mass(kg) x speed²n(m/s/s)
draw and interpret sankey diagram to represent energy transfers
What is the conservation of energy?
Energy cannot be created or destroyed, but can be changed from one form to another.
What is the change in energy when an object is being projected upwards?
When an object is projected upward, then kinetic energy is transferred to gravitational potential energy: the velocity of the object decreases as its height increases.
What is the change in energy when a moving object hits an object?
When a moving object hits an obstacle, the kinetic energy of the moving object is transferred to a number of possible forms of energy: kinetic energy in the obstacle, heat energy & sound energy
What is the change in energy when an object is being accelerated by a constant force?
Work is done by a force on an object. This work is converted to the object’s kinetic store.
What is the change in energy when a vehicle is slowing down?
To begin with, the vehicle’s energy is in the kinetic store. The brakes do work slowing the car down. During this process, energy is dissipated (lost) through heat and sound.
What is the change in energy when bringing water to boil in an electric kettle?
Energy transfers from the electrical store of the mains power supply to the thermal store of the water.
What happens when there are energy transfers in a closed system?
Where there are energy transfers in a closed system there is no net change to the total energy in that system
When do mechanical processes become wasteful?
Whenever work is done mechanically, frictional forces have to be overcome, including things like moving parts rubbing together, and air resistance. The energy needed to overcome these frictional forces is transferred to the thermal energy stores of whatever’s doing the work and the surroundings.
How can you reduce unwanted energy transfer?
Mechanical devices can be made more efficient through lubrication to reduce the friction between moving parts of a machine and increase the amount of useful energy transferred.
Energy loss through windows can be reduced using double glazing. These kind of windows have air or a vacuum between the two panes of glass. Air is a poor conductor, while a vacuum can only transfer energy by radiation. Energy loss through walls can be reduced using cavity wall insulation. This is made up of an inner and outer wall with a gap in the middle to reduce the amount of energy transferred by conduction.
What are the effects of thickness and thermal conductivity of the walls of a building on its rate of cooling qualitatively?
Generally thicker walls slow down the transfer of heat, and higher thermal conductivity of the walls, depending on materials used will increase the rate of transfer.
recall efficiency equation
efficiency = (useful energy transferred by the device) / (total energy supplied to the device)
How can efficiency be increased?
by reducing wasted energy transfers so more of the input energy is usefully transferred.
