Notes for Science

Matter

• The particle model of a Gas• A gas has no fixed shape or volume, but always spreads

out to fill any container. • There are almost no forces of attraction between the

particles so they are completely free of each other. The particles are widely spaced and scattered at random throughout the container so there is no order in the system. The particles move rapidly in all directions, frequently colliding with each other and the side of the container. With increase in temperature, the particles move faster as they gain kinetic energy.

The particle of a liquid• A liquid has a fixed volume at a given temperature but its shape

is that of the container which holds the liquid. There are much greater forces of attraction between the particles in a liquid compared to gases, but not quite as much as in solids. Particles quite close together but still arranged at random throughout the container, there is a little close range order as you can get clumps of particles clinging together temporarily. Particles moving rapidly in all directions but more frequently collisions with each other than in gases due to shorter distances between particles. With increase in temperature, the particles move faster as they gain kinetic energy, so increased collision rates, increased collision energy and increased rate of diffusion.

The particle model of a Solid

• A solid has a fixed volume and shape at a particular temperature unless physically subjected to some force. The greatest forces of attraction are between the particles in a solid and they pack together as tightly as possible in a neat and ordered arrangement. The particles are too strongly held together to allow movement from place to place but the particles vibrate about their position in the structure. With increase in temperature, the particles vibrate faster and more strongly as they gain kinetic energy.

• In evaporation* and boiling the highest kinetic energy molecules can ‘escape’ from the attractive forces of the other liquid particles.

• The particles lose any order and become completely free to form a gas or vapour.

• Energy is needed to overcome the attractive forces in the liquid and is taken in from the surroundings.

• If the temperature is high enough boiling takes place. • Boiling is rapid evaporation anywhere in the bulk liquid and at a

fixed temperature called the boiling point and requires continuous addition of heat.

• The rate of boiling is limited by the rate of heat transfer into the liquid.

• On cooling, gas particles lose kinetic energy and eventually become attracted together to form a liquid.

• There is an increase in order as the particles are much closer together and can form clumps of molecules. – This is why steam has such a scalding effect, its not

just hot, but you get extra heat transfer to your skin due to the exothermic condensation on your surface!

• When a solid is heated the particles vibrate more strongly as they gain kinetic energy and the particle attractive forces are weakened.

• Eventually, at the melting point, the attractive forces are too weak to hold the particles in the structure together in an ordered way and so the solid melts.

• The particles become free to move around and lose their ordered arrangement.

• Energy is needed to overcome the attractive forces and give the particles increased kinetic energy of vibration

• On cooling, liquid particles lose kinetic energy and so can become more strongly attracted to each other.

• Eventually at the freezing point the forces of attraction are sufficient to remove any remaining freedom and the particles come together to form the ordered solid arrangement.

Light

• Light is a form of energy produced by the change in motion of a charged particle. Light does not need a medium (solid, liquid or gas) in order to travel. Electrons moving back and forth will cause light. When the electrons inside of an atom absorb energy they jump to a different energy level. When these electrons fall back down to their original energy level they give off a little packet of energy in the form of light. This packet of light energy is called a photon. Light can either travel as a wave or as a particle.

• Some objects produce their own light will other objects reflect light. These sources of light are called laminated objects. Sources of light include: the sun, a light bulb, a match and a candle. Bioluminescent organisms are living things that can produce their own light. A firefly is an example of a bioluminescent organism. Objects that reflect certain amounts of light are called illuminated objects. Objects that reflect light include: a mirror, the moon and a piece of paper.

• What is so amazing about light is the speed at which it travels. Light travels 186,000miles per second or 299,798 kilometers per second. That means light can travel a distance of 186,000 miles in one second! It takes eight minutes for light from the sun to reach earth. This is why you hear lightening before you see thunder. Lightening and thunder happen at the same time, yet light travels faster than sound so you see the lightening then a few seconds later you hear the thunder.

• When you wake up in the morning and look at yourself in there mirror you are seeing a reflection of yourself. You see your self by the light waves bouncing off of the mirror. Reflection is the bouncing back of a wave. As we see in the diagram to the left. Light waves hit a smooth surface and bounce off with the same angle in which they hit the surface. This is the Law of Reflection: the angle of incidence is equal to the angel of reflection. Since both angles are equal the image appears to be the same. This will happen when we reflect light off of a flat smooth surface.

• What happens when the surface is not smooth? When light bounces off of a rough surface diffuse reflection is seen. Objects appear blurred, like the reflection of the setting sun on the water. We do not get a clear picture of the sun as we would if the light was being reflected off of a mirror.

• Surfaces can also be curved. A satellite dish is a perfect example of a concave surface. The dish is curved inward as to direct all of the light waves in toward the center receiver and then through a cable into your house.

• A security mirror is curved outward (convex surface) as to see the entire store. If you go into 7-11 you will see a curved mirror in the corner. This mirror is designed to spread out the light waves so the clerk can see everything going on in the store.

• White light contains all colors of the spectrum. The image of the prism to the left shows white light entering. The light waves change speed and direction as they pass through the prism. Each of the different colors of light then become separated.

• The colors we see are just reflections of light off of objects. If an object reflects all wavelengths of light then it will appear white. If an object absorbs all wavelengths of light it will appear black. An object is the color of light it reflects. All other wavelengths of light are absorbed.

•For example, a red object reflects red light and absorbs orange, yellow, green, blue, indigo and violet. A green object reflects green light and absorbs red, orange, yellow, blue, indigo and violet.

Heat and temperature

• Temperature is a measure of heat energy. Temperature is measured in degrees Celsius (Centigrade), Fahrenheit, or Kelvin. Some high temperatures:Boiling water at sea level = 100 degrees Celsius; Molten lava = 2,000 Kelvin; Tungsten filament of a light bulb = 4,000 Kelvin;

• Silver melts at 962 degrees Celsius and boils at 2,210 degrees Celsius; Gold melts at 1,064 degrees Celsius and boils at 2,900 degrees Celsius

• Some warm-blooded animals hibernate during cold weather and their body temperature falls to conserve energy. The normal temperature of a hibernating dormouse falls from 98.6 degrees Fahrenheit to 64 degrees; The normal temperature of an opossum falls from 95 degrees Fahrenheit to 50.9 degrees

• Cold-blooded animals lack internal temperature controls so they bask in the sun to keep warm and then hide in the shade to keep cool. They are most active when their body temperatures are greater than 90 degrees Fahrenheit. The salamander is cold-blooded and can survive in temperatures of 42.4 through 79.7 degrees Fahrenheit.

• Does hot water freeze faster than cold water? No, it does not. However, boiled water has less dissolved air and fewer air bubbles; for this reason water that has been boiled might freeze faster and will form ice that is more dense.

• Heat is a form of energy. There are several physical effects of heat including: 1. Changing the temperature of a substance; 2. Changing the state of a substance (as from solid to liquid); 3. Causing expansion of the substance

• Heat is transferred from a substance at a higher temperature to one at a lower temperature by conduction, convection, or radiation. Conduction occurs mainly in solids; convection occurs in fluids, and radiation occurs through space, Radiation occurs without the need for any substance to transfer the heat.

Magnets

• A magnet is an object or material that attracts certain metals, such as iron, nickel and cobalt. It can also attract or repel another magnet. All magnets have North-seeking (N) and South-seeking (S) poles. When magnets are placed near each other, opposite poles attract and like poles repel each other. Various electrical devices make use of magnets.

• Types of magnets• There are permanent magnets, temporary

magnets and electromagnets.• Permanent magnets• A permanent magnet is one that will hold its

magnetic properties over a long period of time.

Temporary magnets

• A temporary magnet is one that will lose its magnetism. For example, soft iron can be made into a temporary magnet, but it will lose its magnetic power in a short while.

Electromagnet

• By wrapping a wire around an iron or steel core and running an electrical current through the wire, you can magnetize the metal and make an electromagnet. If the core is soft iron, the magnetism will diminish as soon as the current is turned off. This feature makes electromagnets good for picking up and dropping objects. Typically DC electricity is used, but AC current will also result in an electromagnet.

• Properties of magnets• Magnets always have two poles, come in various shapes,

and attract or repel other magnets.• Names of poles• All magnets have a North-seeking pole (N) and South-

seeking pole (S). In a compass, the side marked (N) will point toward the Earth's North magnetic pole. Thus, it is called the "North-seeking pole." Also note that the Earth's North magnetic pole is not the same thing as the North Pole. They are actually several hundred miles apart.

• The magnet can be made into various shapes. The bar magnet is the most common configuration.

• Bar magnet• Magnets also can be square, spherical, shaped

like a horseshoe, and even shaped like a donut.

• Horseshoe magnet• If you put an iron plate across the N and S poles of a

horseshoe magnet, that would essentially "short circuit" the effect of the magnetism, such that its strength would not be very great. As soon as the plate was removed, the magnet would regain its full strength. That method is sometimes used in magnets that are temporary to help keep their magnetic properties for a longer time.

• An interesting characteristic of magnets is that when you cut a magnet into parts, each part will have both N and S poles.

• Bar magnet cut into three parts• Attraction and repulsion• Magnets strongly attract iron, nickel and

cobalt, as well as combinations or alloys of these metals.

• Also, unlike poles of two magnets will attract, but like poles will repel. Thus, N and S attract, while S and S will repel each other.

• Creating a magnet• You can magnetize a piece of steel by rubbing a magnet

in one direction along the steel. This lines up the many of the domains or sections of aligned atoms in the steel, such that it acts like a magnet. The steel often won't remain magnetized for a very long time, while the true magnet is "permanently" magnetized and retains its strength for a long time.

• If you use soft iron or steel, such as a paper clip, it will lose its magnetism quickly. Also, you can disorient the atoms in a magnetized needle by heating it or by dropping the needle on a hard object.

• Compass• The first true application of a magnet was the compass, which

not only helps in navigation by pointing toward the North magnetic pole, but it is also useful in detecting small magnetic fields. A compass is simply a thin magnet or magnetized iron needle balanced on a pivot. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.

• Other uses• Magnets are found in loudspeakers, electrical

motors and electrical generators.• A very common application of magnets is to stick

things to the refrigerator. Since the outer shell of most refrigerators is made of steel, a magnet will readily stick to it. The type of magnets used often consists of a thin sheet of a magnetic material.

• As a novelty, magnetic disks can be stacked on a pencil to show magnetic levitation.

• Summary for magnets• A magnet attracts iron, nickel, cobalt and

combinations of those metals. All magnets have North-seeking (N) and South-seeking (S) poles. When magnets are placed near each other, opposite poles attract and similar poles repel each other. Magnets are found in many of our electrical appliances.

The End!

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Done by: Pekhan