physics and chemistry basics
May 7, 1989

#### Work

Work is when a force moves its point of application a distance.. It is represented by the formula W = Fs, where W is work (joules), F is force (newtons) and s is displacement (metres).

More work is done when there is either more force applied or more distance moved. One joule of work is done when a force of one newton moves its point of application one metre.

#### Work and Energy Transfer

Energy transfer is indicated in various ways, eg. a change in temperature shows a transfer of heat energy, while movement of a windmill shows a transfer of kinetic energy.

Two factors that affect the amount of energy transferred by movement is the force required to move an object and the displacement of the object. When work is done energy is transferred. Work done is the change in kinetic energy. Some energy transfer in working is always lost due to the transfer of heat energy.

Displacement involves the distance between two points and the direction of one point to another. Force only does work when the object moves in the direction of the force.

#### Work and Kinetic Energy

In hitting a golfball, the kinetic energy of a swinging golf club is transferred to the stationary golf ball. The change in the kinetic energy of the golfball is shown by the change in its velocity.

The work done can be calculated by knowing the force on the ball on initial impact and the displacement of the ball.

#### Work and Potential Energy

Work can also result from a change in potential energy that is by attraction of the position of the object. Lifting an object increases its potential energy. The further above the ground an object is raised, the greater its potential energy.

Potential energy due to gravity is known as gravitational field energy. Potential energy can also be associated with magnetic and electrical fields.

Work can also be a result of changes in magnetic field energy, like lifting a ballbearing with a magnet, or changes in electrical field energy, like lifting papers with static electricity.

#### Energy Interchanges

The energy interchange involved in a falling object is from the initial potential energy of the object to the increase in the kinetic energy of the object. When the object hits the ground its kinetic energy dereases as does its final potential energy. Energy is dissipated into sound and heat energy.

#### Energy Conservation

Energy Conservation is concerned with both the quality and the quantity of work being done. The first law of Thermodynamics states that "Energy cannot be created or destroyed; it can only change its form".

Energy can only flow spontaneously from systems inwhich the energy is more intense to those in which it is less intense.

Intense energy from the source is described as high quality energy (HQE). Dissipated energy is called low quality energy (LQE). Degradation is the process of going from HQE to LQE.

The Second Law of Thermodynamics says "Energy flows naturally from hot to cool objects. This process can be made to do work".

It is impossible to convert a given amount of energy fully (100%) into work.

Efficiency, as a percentage, can be defined as

(Energy transferred in the desired way/Total enegy transmitted by the source) * (100/1)

In car engines, electric heaters and other forms of machinery, the cost of the energy source is traded off against the efficiency of the energy transfer process. Improvements of efficiency in these are limited by the second law of thermodynamics.

Special ceramics and alloys are used in high temperature and high efficiency engines, eg. titanium in rocket engines - low density and high melting point. This is necessary, since many common materials have limits to their usefulness at high temperatures.

#### Power

Power is defined as the rate of doing work. It is represented by the formula P = W/T P (watts), W (joules), T (seconds)

A watt is the rate of doing 1 joule of work per second.

The power of a device is greater if 1) the same amount of work is done in a shorter time; or 2) more work is done in the same amount of time.

Power is concerned with the rate of energy transfer rather than the mechanism of energy transfer.

#### Chemical Terms

• Protons are +
• Electrons are -
• Protons = Electrons
• Atomic number = protons = electrons
• Mass number = protons + neutrons

• solulant - the thing that dissolves
• solvent - the thing that does the dissolving
• soluble - the property of dissolving
• sparingly soluble - doesn't like dissolving

• ion - an atom that has gained or lost one or more electrons.
• anions - negatively charged ions
• cations - positively charged ions
• covalent bond - a bond where electrons are shared by both atoms
• ionisation - the breaking of a covalent bond (and loss of an electron)

• LIKE DISSOLVES LIKE - ALWAYS. NONPOLAR WILL NOT DISSOLVE IN POLAR.