The Nature of Waves

For many people, the first thought concerning waves conjures up a picture of a wave moving across the surface of an ocean, lake, pond or other body of water. The waves are created by some form of a disturbance, such as a rock thrown into the water, a duck shaking its tail in the water or a boat moving through the water. The water wave has a crest and a trough and travels from one location to another.

Another picture of waves involves the movement of a slinky or similar set of coils. If a slinky is stretched out from end to end, a wave can be introduced into the slinky by either vibrating the first coil up and down vertically or back and forth horizontally. A wave will subsequently be seen traveling from one end of the slinky to the other. As the wave moves along the slinky, each individual coil is seen to move out of place and then return to its original position.

Another example is a long jump rope, the up and down  vibration of the end of the rope created a disturbance of the rope that subsequently moved towards the other end. The shape of the pattern formed in the rope was influenced by the frequency at which we vibrated it. If we vibrated the rope rapidly, then a short wave is created. However, if we vibrated the rope less frequently (not as often), a long wave would be created.

Stable and Unstable Nuclei

The Strong Nuclear Force binds Nucleons together

The Strong Nuclear Force (also referred to as the strong force) is one of the four basic forces in nature (the others being gravity, the electromagnetic force, and the weak nuclear force). As its name implies, it is the strongest of the four.

However, it also has the shortest range, meaning that particles must be extremely close before its effects are felt. Its main job is to hold together the subatomic particles of the nucleus (protons, which carry a positive charge, and neutrons, which carry no charge. These particles are collectively called nucleons). As most people learn in their science education, like charges repel (+ +, or - -), and unlike charges attract (+ -).

If you consider that the nucleus of all atoms except hydrogen contain more than one proton, and each proton carries a positive charge, then why would the nuclei of these atoms stay together? The protons must feel a repulsive force from the other neighboring protons. This is where the strong nuclear force comes in. The strong nuclear force is created between nucleons by the exchange of particles called mesons. This exchange can be likened to constantly hitting a ping-pong ball or a tennis ball back and forth between two people. As long as this meson exchange can happen, the strong force is able to hold the participating nucleons together.

         

Alpha Emission Happens in Very Big Nuclei

1. Alpha emissions only happens in very big atoms (with more than 82 protons), like uranium and radium.
2. The nuclei of these atoms are just too big for the strong nuclear force to keep them stable.
3. When an alpha particle is emitted: the Proton number decreases by two, and the nucleon number decreases by four.

Beta Emissions Happens in Neutron-Rich Nuclei

1. Beta-minus decay is the emission of an electron from the nucleus along with an antineutrino.
2. Beta decay happens in "neutron rich" isotopes.
3. When a nucleus emits a beta particle, one of the neutrons in the nucleus is changed into a proton.

• Proton number increases by one, and the nucleon number stays the same.

Atomic Structure

Atoms are made up of Protons, Neutrons and Electrons

Inside every atom, there's a nucleus containing protons and neutrons. Protons and neutrons are both known as nucleons. Orbiting this core are the electrons. This is the nuclear model of the atom.

The following are the properties of electrons, protons and neutrons in the table:

Atoms are Really, Really Tiny

Each atom is about a tenth of a nanometer (1 x 10^-10m) in diameter. To give you that in context, you'd need to line up around 4 million iron atoms side by side to give you a line 1 mm long. If you think that's small, try the nucleus.

1. Although the proton and neutron are 2000 times more massive than the electron, the nucleus only takes up a tiny proportion of the atom. The electrons orbit at relatively vast distances.
2. The nucleus is only 10 000th the size of the whole atom - most of the atom is empty space.
3. If we were to shrink the Solar System (including poor rejected Pluto) so the Sun was the size of a gold nucleus, Pluto would only be half as far away as gold's first electron.

Isotopes have the Same Proton Number, but Different Nucleon Numbers

Atoms with the same number of protons but different number of neutrons are called isotopes.

• Changing the number of neutrons doesn't affect the atom's chemical properties.
• The number of neutrons affects the stability of a nucleus though.
• In general, the greater the number of neutrons compared with the number of protons, the more unstable the nucleus.
• Unstable nuclei may be radioactive and decay to make themselves stable.

~The Nucleon Number is the Total Number of Protons and Neutrons.

Young's Modulus

Introduction:

Young's modulus is a measure of how difficult it is to compress a material, such as steel. It measures pressure and is typically computed in terms of pascals (Pa). It is most commonly used by physicists to determine strain, a measurement of how a material, responds to a pressure, such as being squeezed or stretched.

Steel in Young's Modulus:

Understanding that steel is extremely hard to compress is important in everyday life. For example, it can be used to construct buildings and not become compressed, ruining the integrity of the building structure. A cube of steel that is only 1 meter (3.28 ft) in width, height, and depth, would only compress about one micron

while supporting the weight of one school bus, because of the amount of pressure it can withstand. In comparison, a cube that is comprised of the same dimensions and is made of lead has a lower value for Young's modulus. The lead cube would compress 14 times more than the steel cube.

Powerful Alloys

Titanium Alloys

Titanium (Ti) is a lightweight metal which forms amazing alloys with aluminium, vanadium, tantalum, niobium etc. These alloys are hard while being light. Initially, they were used in aerospace and aviation for making aircraft bodies. But now more applications are being found in automobile and general engineering. For example, the Tata Chemicals factory at Mithapur (India) uses huge Ti-alloy vessels for processing caustic soda (sodium hydroxide), which will otherwise corrode stainless steels in seconds.


Ti-alloys are difficult to weld and cut, hence they have not edged out steels. But they rule the roost in bio-medical implants. Ti alloys are now common in making jewellery, golf-clubs, expensive watches... there's a lot that can be done!

                   ***************************************************************

Hooke's Law

The Trampoline

Hooke's law deals with springs and equilibrium. A trampoline is essentially an elastic disc that is connected to several springs. As you land on the trampoline the springs and the trampoline surface stretches as a result of the force of your body landing on it. 
Hooke's law states that the springs will work to return to equilibrium. In other words, the springs will pull back against the weight of your body as you land. The magnitude of this force is equal to that which you exert on the trampoline when you land. Hooke's law is stated in the following equation: F = -kx where F is force, k is the spring constant and x is the displacement of the spring. Hooke's law is merely another form of potential energy. Just as the trampoline is about to propel you up, your kinetic energy is 0 but your potential energy is maximized, even though you are at a minimum height. This is because your potential energy is related to the spring constant and Hooke's Law.

Intro of Density

Different densities of fluids.

Density is something that affects many of our everyday decisions. Consciously or not, we make mental calculations of density every time we interact with the physical world around us. Can we slide that box? Can we lift that rock? 

People are often confused about the difference between weight and density. There is an old riddle which highlights this confusion: “What weighs more – a pound of feathers or a pound of lead?” The answer, of course, is that both weight same – one pound. However, feathers are much less dense than lead, and therefore take up much more space. Density is the ratio of an object’s mass to its volume. This means that to find density, you must measure an object’s mass and divide it by the amount of space it takes up. The standard units of density are [kg/m3], although other units are commonly used such as [g/ml], [g/cm3], or [kg/l]. 1 ml has the same volume as 1 cm3.