An electric car building up speed (accelerating)
Teaching Guidance for 14-16
What's the energy story when an electric car is increasing its speed?
Wrong Track: Chemical energy in the battery is transferred to kinetic energy of the car and this then goes to heat energy in the surroundings. Chemical energy (battery) → kinetic energy (car) → heat energy (surroundings: air, road, car).
Right Lines: When the electric car is speeding up, energy is shifted from the chemical store of the battery both to the kinetic store of the car and to the thermal store of the surroundings: energy (chemical store: battery) → energy (kinetic store: car) → energy (thermal store: surroundings).
Using multiple levels of description explicitly
Thinking about the teaching
Once again, it's helpful to think of this process in terms of physical, energy and pathway descriptions.
The physical picture to have in mind here is one of the car building up speed (accelerating) and also warming up the air around it, with the car battery gradually
In energy terms we'd say that the chemical store of the battery is gradually emptying while the kinetic store of the car is filling and the thermal store of the surroundings is also filling.
A different perspective is portrayed when thinking about pathways. Here the car's electric motor is the central device. On
one side of the motor, there's an electric circuit – an electrical working pathway along which energy is shifted from the battery to drive the motor. On the
other side of the motor, there are mechanical linkages that enable the motor to drive the car forward – there is a mechanical working pathway along which energy is shifted as the motor drives the car forward. Furthermore, there's a heating by particles pathway along which the thermal store of the surroundings is filled. The power in the input pathway (electrical working) is switched to both output pathways (mechanical working and heating by particles).