Forces v Energy (Part I)…

A thing that often causes a little confusion is the distinction between energy (the capacity to do work – measured in joule) and forces (which are simply pushes or pulls – measured in Newton). It is very important to read exam questions very carefully to avoid using the wrong one.

Energy

There are three forms of potential energy – this means ways in which energy can be stored.

Gravitational potential energy – something can do some work when it is lifted off the ground. Mostly just falling back down to the ground with a thud – but it is still work!

Chemical potential energy – the energy stored in food, hydrocarbon fuels, nuclear fuels, explosives and batteries.

Elastic potential energy – sometimes called stretch potential or strain potential energy it is the energy that can be stored in springy materials. Examples include the energy stored in an inflated balloon, or pressurised gas; the energy stored in stretched bow string or withdrawn catapult; or the energy locked up in the spring of a clockwork toy or clock.

There are also five examples of energy in action – where the work is being done right there.

Kinetic energy – this is the energy that any moving object has.

Thermal energy – more commonly called heat. Everything above absolute zero (so that means everything) has some thermal energy.

Sound energy – the energy of pressure waves travelling through the air.

Light energy – this is sometimes called radiation energy and refers to the energy of electromagnetic radiation such as ultra violet light, visible light, radio waves and x-rays. Thankfully we usually only need to be concerned about visible light.

Electrical energy – the energy of the flow of electrons within a circuit.

A machine that can convert any of these forms of energy from one for to another is called a transducer. All transducers obey one of the fundamental laws of the Universe – conservation of energy. This states that energy cannot be created or destroyed but it can be changed from one form to another.

I have written about it on a number of occasions, usually in connection with an extraordinary claim of a perpetual motion machine or some other gadget that runs for ever. You should look here, here, here or here for past posts that discuss ideas about energy and energy changes.

I will write more about forces tomorrow.

Questions…

1. Name a transducer which…
   • (a) converts electrical energy into kinetic energy
   • (b) converts electrical energy into sound energy
   • (c) converts chemical potential energy into light energy and thermal energy
   • (d) converts sound energy into electrical energy
   • (e) converts light energy into electrical energy
2. What energy change does a dynamo do?
3. How many kilojoules should a reasonably active adult male have in their daily diet?
4. Which two components of your diet contribute the most energy?