Things that speed up and slow down
Physics Narrative for 14-16
Mechanical working is a kind of accumulating
Controlling motion by switching from an electrical pathway to a mechanical pathway happens everywhere. Try counting the electrical motors in your home (washing machine, blender, hard disk, vacuum cleaner…). Then add to this total the number of loudspeakers, because these also switch between the same pathways, and they are examples where control over the switching is paramount. Life without these devices would be very different. As with the more complicated heating devices, the details are often complex but the energy story remains clear and simple.
Power accumulates energy in the kinetic store, by mechanical working, as the object speeds up or slows down. Energy can be shifted by mechanical working because of the switch in the power from electrical working.
Motors and loudspeakers come with many different working powers, showing the maximum rate at which energy can be shifted – the maximum power that the device can switch. Usually failure is as a result of excess dissipation in a thermal store – often the coil of wire that forms an essential part of the design of these devices. The coil melts.