Work and Energy

Hey there,
Since you should be enjoying your last days of holiday ( I'm enjoying them anyway), I'll just be adding a short post today. It's about work and energy. Maybe better: Work or Energy.

All objects contain energy. This energy makes them capable to perform "work". So, for energy, we use the same unit as for work: the joule. The energy in an object can be divided in 2 categories:

• Potential energy: The energie an object contains because it's located in a gravitational field.
• Kinetic energy: the energy an object contains because it has a certain speed
• (All matter also contains energy. Because trough out the entire universe, matter and energy can be converted, and the total stays constant, according to Einsteins formula: E=mc²)

The total of these tree energy types in an object always stays constant. And because in the early exercises, we won't be using the mass-energy, we can say that the 'total energy', consisting of kinetic and potential energy, remains constant. More about this later.

Oké, this was just an 'Intermezzo'. Next topics will be about potential and kinetic energy.
bye

Work: A force on the move

It was a difficult decision, but I thought it would be better to see "work" before pressure, although I find it more difficult. But let's give it a go.

Work in physics isn't the same as work as we know it. In physics, we say work is done by a force on an object only if:

• The object displaces.
• the direction of the displacement isn't at right angles with the direction of the force.

We define this 'work' as the product of the force acting on the object and the distance through which the object moves. Or

W = F. d(x)

If we insert the units Force and Distance, we get the unit of Work, the Joule:

J = N . m

Sometimes, the direction of the force isn't the same as the direction of the movement. For example, if a boat is pulled by boatman with a rope:

Here, we have a pulling force, F, which pulls in the movement direction. If we want to determine the part of the force that moves the boat, we have to project the force on the direction of the movement. If we do so, we get Fm = F . cos(a). So, the work done by the force F, with regard only to the direction of the movement, is:

W = Fm . d(x) => W = F . cos(a) . d(x)

These are the basics to work. It's probably verry abstract, but it will become clearer in the next posts about work to move objects etc.

Technorati labels: Work, Joule