General Science: Physics - University of Mindanao PDF

University of Mindanao – Competency Appraisal General Science GENERAL SCIENCE: PHYSICS 1. Mechanics A. Motion – change in position with respect to a reference point a. Physical quantities used to describe motion:...

University of Mindanao – Competency Appraisal General Science GENERAL SCIENCE: PHYSICS 1. Mechanics A. Motion – change in position with respect to a reference point a. Physical quantities used to describe motion: Distance – length of path covered or travelled by an object moving from an initial to a final position; scalar quantity Displacement – measure of how far an object has moved in a particular direction from its original position; vector quantity Speed – how fast something is moving; scalar quantity ▪ Instantaneous speed – speed at an instant (i.e. as read in the speedometer) ▪ Average speed – total distance travelled divided by the total time of travel Velocity – the rate of change in displacement of an object at a given time interval; vector quantity Acceleration – rate of change of velocity over time; vector quantity b. Uniform Motion An object moving with a uniform speed/velocity has zero acceleration The moving object will cover the same distance at the same time interval There is zero net force acting on the object Useful equation: velocity = distance/time (v=d/t) Exercise: A car travels a distance of 150 kilometers in 3 hours. What is the car's average velocity? c. Accelerated Motion When a moving object changes its velocity, then the motion of the object is said to be accelerated. Three ways to change velocity: (1) change in speed (2) change in direction (3) change in both speed and direction 1 University of Mindanao – Competency Appraisal General Science Useful equation Exercise: A car starts from rest and reaches a velocity of 20 m/s in 5 seconds. What is its acceleration? d. Uniformly Accelerated Motion Free fall - the object in motion is solely under the influence of gravity, thus the acceleration is constant (acceleration due to gravity) which is equal to 9.8 m/s2. Useful equation: 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 𝑔𝑟𝑎𝑣𝑖𝑡𝑦 𝑥 𝑡𝑖𝑚𝑒 𝑜𝑟 𝒗 = 𝒈𝒕 Exercise: A ball is dropped from a tall building. If it falls freely for 3 seconds, what will be its velocity just before it hits the ground? B. Force - an interaction between objects that causes them to change motion Balanced force - equal in magnitude and opposite in direction, the forces cancel each other, and the net force is zero Unbalanced force - not equal and there is a net force Fnet C. Newton’s Laws of Motion a. Law of Inertia An object at rest will remain at rest, and an object in motion will remain in motion with a constant velocity unless acted upon by an external force. 2 University of Mindanao – Competency Appraisal General Science b. Law of Acceleration When enough force is applied, the object will accelerate. The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, it is expressed as F = ma, where F is force, m is mass, and a is acceleration. c. Law of Interaction For every action, there is an equal and opposite reaction. This means that when one object exerts a force on another, the second object exerts an equal force in the opposite direction on the first object. D. Newton’s Law of Universal Gravitation – every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. 𝐺𝑟𝑎𝑣𝑖𝑡𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑮 = 𝟔. 𝟔𝟕 𝒙 𝟏𝟎−𝟏𝟏 𝑵𝒎𝟐 /𝒌𝒈𝟐 Exercise: Determine the gravitational force between a 60-kg and 70-kg person who are both standing 2.0m apart. 3 University of Mindanao – Competency Appraisal General Science E. Energy - ability of an object to do work Potential energy – stored energy due to position; object at rest 𝑃𝐸 = 𝑚𝑎𝑠𝑠 𝑥 𝑔𝑟𝑎𝑣𝑖𝑡𝑦 𝑥 ℎ𝑒𝑖𝑔ℎ𝑡 𝑷𝑬 = 𝒎𝒈𝒉 Exercise: A book with a mass of 2 kg is placed on a shelf 3 meters above the ground. What is its gravitational potential energy? Kinetic energy – energy of motion; object in motion 1 𝟏 𝐾𝐸 = 𝑚𝑎𝑠𝑠 𝑥 (𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦)2 𝑲𝑬 = 𝒎𝒗𝟐 2 𝟐 Exercise: A soccer ball with a mass of 2 kg is moving with a velocity of 3 m/s. What is its kinetic energy? Law of Conservation of Energy – the total energy of an isolated system is conserved. Energy is neither created nor destroyed but is just transformed from one form to another. F. Work Work is done on a system or an object whenever a force applied on that object causes change in the position (displacement) of an object. Work is done when a force is applied to an object, and the object moves in the direction of the applied force. o Ex. Pushing a box and it moves. No work is done when a force is applied, but it does not cause displacement, or the displacement is perpendicular to the force. o Ex. Pushing a wall. o Ex. Carrying a bag while walking forward. Mathematically, work is given by: 𝑊𝑜𝑟𝑘 = 𝐹𝑜𝑟𝑐𝑒 𝑥 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑾 = 𝑭𝒅 Exercise: A person pushes a box with a force of 10 N across the floor for a distance of 5 m. How much work is done on the box? 4 University of Mindanao – Competency Appraisal General Science 2. Heat and Temperature a. Temperature - measure of the average kinetic energy of the molecules of a substance; the greater the temperature of a substance, the greater the motion of its molecules Scale Freezing Boiling Absolute Unit Conversion formula point point zero interval Fahrenheit (°F) 32 °F 212 °F -459.67 °F 180 °C = (°F - 32) × 5/9 Celsius (°C) 0 °C 100 °C 273.15 °C 100 °F = (°C × 9/5) + 32 Kelvin (K) 273.15 K 373.15 K 0K 100 K = °C + 273.15 Exercise: (1) The temperature outside is 25°C. What is this temperature in Fahrenheit? (2) A weather report says the temperature is 50°F. What is this in Celsius? (3) A scientist measures a temperature of 30°C. What is this in Kelvin? b. Heat – measure of the internal energy that has been absorbed or transferred from one body to another Heating - process of increasing internal energy Cooling - process of decreasing internal energy c. Heat Transfer Heat always transfers from a region of higher temperature to a region of lower temperature until thermal equilibrium is reached. (1) Conduction – heat is transferred through direct contact between particles in a solid or between objects in physical contact (2) Convection –heat is transferred through the movement of fluids (liquids or gases) due to differences in temperature and density (3) Radiation – heat is transferred in the form of electromagnetic waves, requiring no medium for propagation 5 University of Mindanao – Competency Appraisal General Science d. Thermodynamics – study of heat and its transformation to work or mechanical energy First Law of Thermodynamics › is based on the law of conservation of energy which states that energy cannot be created or destroyed, only transformed from one form to another › when heat is added, it is converted to other forms of energy Second Law of Thermodynamics › emphasizes the direction or flow of heat › states that heat flows naturally from a hot object to a cold object › Heat engine – any device that absorbs heat and partially converts this into mechanical work › Heat pump – device that transfers heat from a cooler area to a warmer area using mechanical work, effectively moving thermal energy against its natural direction of flow; a reverse of heat engine, used in refrigerators 3. Electricity a. Conductors – materials that allows charges to through it b. Insulators – present significant resistance to flowing charges c. Ohm’s Law – states that electric current is directly proportional to the voltage and inversely proportional to the electrical resistance Voltage (V) – the pressure that creates current flow in a circuit Current (I) – the flow of electrons through a circuit Resistance (R) – the opposition to current flow by electric components in the circuit Exercise: A 3.0 V battery is used to light up a 9.0 Ω bulb of a flashlight. How much current is drawn in the circuit? 6 University of Mindanao – Competency Appraisal General Science d. Coulomb’s Law – describes the force between two point charges; the force of attraction or repulsion between two charged bodies is directly proportional to the product of the two charges and inversely proportional to square of distance between them Like charges repel each other; unlike charges attract. Thus, two negative charges repel one another, while a positive charge attracts a negative charge. 𝑭 𝑖𝑠 𝑡ℎ𝑒 𝑚𝑎𝑔𝑛𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑓𝑜𝑟𝑐𝑒 𝑖𝑛 𝑁𝑒𝑤𝑡𝑜𝑛 𝒒𝟏 𝑖𝑠 𝑡ℎ𝑒 𝑚𝑎𝑔𝑛𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑓𝑖𝑟𝑠𝑡 𝑐ℎ𝑎𝑟𝑔𝑒 𝑖𝑛 𝑐𝑜𝑢𝑙𝑢𝑚𝑏𝑠 𝒒𝟐 𝑖𝑠 𝑡ℎ𝑒 𝑚𝑎𝑔𝑛𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑒𝑐𝑜𝑛𝑑 𝑐ℎ𝑎𝑟𝑔𝑒 𝑖𝑛 𝑐𝑜𝑢𝑙𝑢𝑚𝑏𝑠 𝒓 𝑖𝑠 𝑡ℎ𝑒 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑡ℎ𝑒 𝑐ℎ𝑎𝑟𝑔𝑒𝑠 𝑖𝑛 𝑚𝑒𝑡𝑒𝑟𝑠 𝐶𝑜𝑢𝑙𝑜𝑚𝑏 ′ 𝑠 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝒌 = 𝟗. 𝟎 𝒙 𝟏𝟎𝟗 𝑵𝒎𝟐 /𝑪𝟐 Exercise: What is the magnitude of the force on a charge of 4 x 10-9 C that is 5m from a charge if 5 x 10-8 C ? 7 University of Mindanao – Competency Appraisal General Science 4. Waves and Optics a. Waves - disturbances that transfer energy through a medium or empty space, characterized by the propagation of oscillations or vibration Longitudinal wave – the disturbance is parallel to the direction of propagation; in back-and-forth direction Transverse wave – the disturbance is perpendicular to the direction of propagation; in up and down direction Properties of Wave o Wavelength (λ) – The distance between two consecutive points that are in phase on a wave, such as crest to crest or trough to trough in a transverse wave, or compression to compression in a longitudinal wave. It is measured in meters (m). o Amplitude (A) – the maximum displacement of a wave from its rest position. o Frequency (f) – the number of complete wave cycles (wavelengths) that pass a given point per second. It is measured in hertz (Hz), where 1 Hz = 1 cycle per second o Period (T) – the time taken for one complete wave cycle to pass a given point. It is the inverse of frequency and is measured in seconds (s); T=1/f o Wave speed – describes the speed and direction of the wave motion ▪ Useful equation: 𝑤𝑎𝑣𝑒 𝑠𝑝𝑒𝑒𝑑 = 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ (𝜆) 𝑥 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦(𝑓) Exercise: A wave is traveling at a speed of 20 m/s and has a wavelength of 4 meters. What is its frequency? 8 University of Mindanao – Competency Appraisal General Science b. The Electromagnetic Spectrum (1) Radio wave (2) Microwave (3) Infrared (4) Visible light (5) Ultraviolet (6) X-ray (7) Gamma ray c. Properties of Light Reflection – bouncing back of light when it strikes the surface of an object o Regular reflection – light that strikes a smooth, flat and shiny surface is reflected in one direction o Diffuse reflection – light is reflected by a rough-textured or uneven surface is scattered in many different directions Refraction – bending of light as it passes through a different medium, caused by the change in its speed Dispersion – a separation of white light into several rainbow colors after passing a prism Interference – when two or more light waves overlap, they can produce patterns of constructive and destructive interference o Constructive interference – occurs when two waves are in phase and their amplitudes are added together, results to greater amplitude o Destructive interference – occurs when two waves are out of phase and their amplitudes are subtracted from each other, results to smaller amplitude or no wave at all Diffraction – the bending or spreading of waves around obstacles or through narrow openings, causing them to deviate from their original path 9 University of Mindanao – Competency Appraisal General Science Polarization – phenomenon of restricting the vibrations of light to a particular plane perpendicular to the propagation of light o Unpolarized light - consists transverse waves vibrating in all conceivable random directions o Polarized light – plane-polarized; light is vibrating in one direction only d. Mirrors One of the applications of reflection of light can be seen in mirrors, reflecting surfaces and other optical instruments. Mirror is a highly reflective surface made of glass or polished metal, that reflect light without diffusing so that it will give back a clear image of anything placed in front of it. Plane Mirror – has flat reflecting surface; image formed is always virtual, upright and same size of the object Concave Mirror – a spherical mirror with an inward-curving reflective surface; can produce a variety of images—real or virtual, inverted or upright, and of varying sizes—depending on the object's position relative to the mirror Convex Mirror – a spherical mirror with an outward-curving reflective surface; always forms virtual, upright, and smaller images, regardless of the object's position 10