Solids, Liquids and Gases
In a solid, the particles are tightly packed and so they can not easily move around. the bonds between the particles are very strong and the particles to do not have enough energy to move freely. Therefore, solids have fixed shapes. And although the particles are tightly packed, they are always vibrating. When solids are given more energy, usually through heat, the particles start to get more and more excited and vibrate faster and faster. Eventually the particles have enough energy to break the bonds holding the solid together. The solid is now a liquid. This process is called melting. In liquids, the particles can move around freely. The particles move around to take up the shape of the container they are currently in. Also, they move with the help of a force called gravity. The particles in liquids still remain in contact with each other, also liquids cannot be squashed. If even more energy is put into the substance, the articles move more and more until all the bonds are completely broken. The substance is now a gas. Gases spread out to fill any space available and can also be squashed as the particles are well spaced out.Physical changes
Through physical changes nothing new is made but there is a change in appearance. Examples of changes in appearance are state changes, which change the shape, and dissolving. These changes are reversible. Examples of physical changes are ice melting, liquids freezing, rain-water evaporating and steam condensing.
Chemical changes
Differentiating from physical changes, chemical changes always form a new substance. These changes involve a change in appearance, for example a change in colour, or a detectable energy change, which could involve heat, light or sound. Examples of chemical changes are fireworks, frying an egg, burning wood and burning a candle.Expansion and Contraction
When solids, liquids and gases get hotter, the particles vibrate faster and faster. This makes the substances expand, which means the substance takes up more space. But when the particles in solids, liquids and gases cool, they vibrate slower and slower, which makes the substance contract, hence, the substance takes up less space. Because of this, objects that have been built, are built so that they have space to expand. An example of this is railway lines; the railways lines are built in sections with gaps in between, so that when the sun heats the tracks, they have enough space to expand.Brownian Motion
The discovery of Brownian Motion is named after the scientist who first noticed the motion of particles, Robert Brown. Brownian Motion is the random movement of particles in a fluid (liquid or gas). The particles move around and if they randomly bump into each other they change their direction and carry on moving. The particles can also bump into objects visible to the naked human eye. For example we can see it happening in potassium permanganate and water, in ink and water and when methane is released into the air. Another term for Brownian Motion is the Particle Theory, but this term is mostly used in Mathematics.Diffusion
Diffusion is the movement of particles from an area of high concentration to an area of low concentration. This can happen in any fluids (liquid or gas). The higher the temperature of the area in which the fluids are diffusing, the faster the fluids will diffuse. Examples of gases diffusing are flower scents in air, smoke in air and the stench of rotten vegetables in air. Examples of liquids diffusing are ink in water and potassium permanganate in water.
First of all, to understand the conservation of mass you should know that atoms are the smallest part of an element in a chemical reaction. In a chemical reaction the total mass of reactants is always equal to the total mass of products. During any chemical reaction the atoms in the reactants are rearranged to form the products; no particles are created or destroyed, just rearranged. So basically in a chemical reaction the total mass before, will always be the same as the total mass afterwards.Conservation of Mass
Sound
The pitch/frequency of a note is measured in Hertz (Hz). A frequency is the number of sound waves per second. The more sound waves measured, the higher the frequency will be, i.e. if there's 8 waves the frequency will be 8 Hz per second. Below are a few examples of different sounds and what their average frequency would be:- Average male voice - 200 Hz
- Average female voice - 300 Hz
- Bass guitar - 100 Hz
- Middle A on a piano - 450 Hz
- Average baby crying - 1000 Hz
Hearing sound
First of all, sound waves are collected by the ear lobe/pinna. The waves then travel along the ear canal. The waves make the ear drum vibrate. The ossicles (small bones) amplify the vibrations. The cochlea turns the vibrations into electrical signals. The auditory nerve takes the signal to the brain.
Speed of Sound
The speed of sound varies on the conditions of each environment. These conditions include humidity, temperature and altitude. Although to work out sound the equation distance divided by time should be used.Ultrasound
Anything above 20,000 Hz is identified as ultrasound. Humans cannot hear ultrasound; however bats can. We can use ultrasound several different ways. For example to check pregnancies or to clean. This is another way ultrasound can be used: gel is used to absorb an sound wave into the body. The wave will reflect back and a sensor will sense the wave being reflected. On special computers the wave will be analysed so that we can understand what is happening inside the body.
