The fields of physical science are physics, chemistry, astronomy, geology, and meteorology. Under those categories we learned about topics like gravity, sound, motion, power, energy, heat, and others, and even some sub topics such as machines, spring mass systems, and pendulums. We began Physical Science in September. It was intense but fascinating. I am going to tell you about the things that interested me the most.
Variables: There are two types of variables – a dependent and independent variable. A dependent variable is one that changes in response to another variable. An independent variable is one that is controlled or changed to study what effect it has on the dependent variable.
Velocity and Acceleration: Velocity is the change in position with respect to time. Acceleration is the rate at which the velocity of a body changes over time.
Fun fact: the earth’s exact mass is 5.972×10 to the 24th power.
Four known universal forces: Those are the force of gravity, electromagnetic force, weak nuclear force, and strong nuclear force.
Momentum: The momentum of an object is the product of the object’s mass and velocity.
Damping: Damping can take many forms. Friction within the system or some fluid resistance to motion is called viscous damping. That is the most common form of damping and is used in a mechanical system to reduce vibrations. Forced vibrations occur when a system is exposed to a force that varies with time. Pushing someone on a swing is an example of forced vibration.
Pressure and buoyancy: Bernoulli’s Principle states that as the speed of a fluid goes up, its pressure goes down. The pressure in a fast moving stream of fluid is less than the pressure in a slower stream.
Temperature: This is one of the most important things we learned. The equation for converting fahrenheit to celsius is: fahrenheit number minus 32 multiplied by 5/9 equals the celsius number. There’s a form of temperature called “Kelvin” which is different from fahrenheit and celsius, but it’s not used that commonly.
Electromagnetic force and electric charge laws: Coulomb’s Law states that electric charges alike to each other repel each other, and charges opposite to each other attract. Ohm’s Law is another law that states that the current through something is directly proportional to the voltage across the object and is inversely proportional to the resistance of the object. Parallel circuits and power in circuits are affected by these laws.
Introduction to Sound: Amplitude is the maximum displacement of the sound wave. Period is the amount of time it takes the object to make one complete oscillation, usually given in units of seconds. Cyclical Frequency is the number of cycles/oscillations per one second. This is called Hertz (Hz) and has units of one second. Wave length is the distance between two identical points in a wave, after the wave has made one complete cycle. Wave speed is the speed at which a wave moves. The abbreviations for sound terms are: V = velocity, f = frequency, ? = wavelength. Other important points with sound are that sound can pass through any elastic medium, something elastic can be deformed or reshaped, all materials are elastic to a certain degree, sound requires a medium to pass through. Sound waves below 20 hertz are called infrasonic, and sound waves above 20,000 hertz are called ultrasonic.
Speed and transmission of sound: The speed at which sound travels depends on the medium it passes through and is independent of any characteristic of the sound such as frequency or amplitude. Each material has its own speed how sound travels through it. Speed higher in liquids than in gasses and higher in solids than in liquids. In gasses like air, increasing temperature increases the speed of sound. Typically the speed of sound in air is 340 meters per second, but it changes due to temperature. Like light, when sound encounters a surface, it can bounce off or continue into the surface. Smooth hard surfaces tend to reflect sound, soft irregular surfaces tend to absorb it. When sound gets bounced back, it creates reverberations. The law of reflection states: “the angle of reflection is equal to the angle of incidence.” Also a fun fact is that SONAR means Sound Navigation And Ranging. Sonar sends out a sound and measures the time it takes to come back from being reflected off an object. The study of sound is called acoustics.
Sound, resonance, and interference: Sound will create a varying force on the object, that is known as frequency of the sound. Resonance can break things. This is because the vibrations keep getting bigger and bigger until the system falls apart. Constructive interference occurs when two waves meet, combine, and have an increased amplitude. Destructive interference occurs when two waves meet, combine, and reduce an increased amplitude. When two objects each create a sound wave and the sound waves are close to the same frequency, a beat is produced. This is caused by both constructive and destructive interference and creates a low frequency sound wave.
Doppler effect and sonic booms: The doppler effect is when a sound source travels, it causes the frequency of the sound to be higher in the direction the object is traveling and lower in the direction opposite that it is traveling. Bow waves are when the waves overlap and form a V shaped wave, that wave is called a bow wave. In three dimensions the waves are spherical rather than circular. When they overlap it forms a cone rather than a V.
Sonic Booms are when an object travels faster than the speed of sound it produces a conical shock wave, and when that shock wave encounters an observer, it hears a sonic “boom”, or “crack.” A sonic boom is not the sound of the sound barrier being broken. It is merely a shock wave created because of the compression of the sound wave created into a shock wave.
Light and its propagation: the properties of electromagnetic waves are that they behave like a wave, but their speed depends only on the medium through which they travel through. Their speed differs with the medium, and they can travel through a vacuum. Light is an electromagnetic wave, and all electromagnetic waves travel at the same speed as a vacuum. The speed of light in a vacuum is 300,000 kilometers per second. A material is transparent to a frequency of light if the light can pass through it. A material is opaque to a frequency if the light cannot pass through it. A material can be opaque to some frequency but transparent to others. Most found materials are opaque. The definition of opaque is “not able to be seen through; not transparent.”
Reflection, refraction, and diffraction of light: Light is a wave, therefore it can be reflected. Reflection of light can either be specular or diffuse. A specular reflection follows the law of reflection which says when a light ray is incident on a plane surface, the incident ray, the reflected ray and the “normal” to the surface of the mirror all lie in the same plane. It also states that the angle the incident ray makes with the normal is equal to the angle that the reflected ray makes with the normal. A mirror is an example of specular reflection. A diffuse reflection scatters the incoming light ray in all directions, reflective tape is a good example. Light is refracted the same way other waves (such as sound) are refracted. Each material has what is called an index of refraction, which is the ratio of the speed of light in a vacuum to the speed of light in the material. How much a ray of light is bent going from one material to another is influenced by each of the material’s index of refraction. Diffraction of waves occurs when the waves pass around an object or through a narrow opening.
Color: is a specific frequency of light. White light is a combination of all the colors and red is the lowest frequency we can see. Violet is the highest. Some objects are transparent to only one color and opaque to others. This is called selective transmission. The Doppler effect also works on light. Astronomers use this to determine if celestial bodies are moving towards or away from the earth.
Internal reflection and dispersion of light: the optical phenomenon of internal reflection occurs when the index of refraction is such that a light ray, rather than passing from one medium into another is actually bounced back into the medium. At some angles all of the light is reflected back. Different frequencies of color will diffract at different angles. This is why prisms make rainbows.
Reviewing sound, color, and light: Light from the sun or a lightbulb is created such that the electromagnetic waves vibrate in all directions. If you were able to see the actual individual light waves coming at you, some visible waves would be vibrating up and down, some left and right, and some at other angles. One type of mirror is the curved mirror which can create real images and is able to make an image larger than the original therefore creating magnification. Two different types of lenses are converging lenses and diverging lenses. The focal length of the lens is the distance from the lens to where parallel rays of light coming through the lens converge. A thin lens is a lens whose thickness is an extremely small compound to the lens length. Just as we were able to determine image size and location using ray tracing with mirrors, we can do the same thing using lenses. Even the best mirrors absorb some of the light that they reflect. Consequently, the image is not as bright as it could be. Because of internal reflection a glass prism can reflect light and can even reflect more light than a mirror. All in all, I learned more than I already knew about science and physics thanks to this course. It taught me much about how science and physics affects the world around us.
