SCIENCE G8 Q2 notes - PDF

SCIENCE G8 Q2 notes Newton’s Laws of Motion Force and Interaction Force - Push or pull - Vector quantity (magnitude & direction) - Contact & non contact - Measured in Newtons (N) Center of Mass - It is a point where any uniform force on the object acts - For uniform object...

SCIENCE G8 Q2 notes Newton’s Laws of Motion Force and Interaction Force - Push or pull - Vector quantity (magnitude & direction) - Contact & non contact - Measured in Newtons (N) Center of Mass - It is a point where any uniform force on the object acts - For uniform objects, the center of mass is located at the centroid Free-Body diagram - Used to show the relative magnitude and direction of all forces acting upon an object in a given situation Net force = ΣF When two or more forces act on an object, the net force is the sum of all the forces acting on it. Contact Forces Contact Force: Normal Force - A force exerted upon an object that is in contact with another stable object. The direction of the force is always perpendicular to the surface. Contact Force: Tension Force - Force that is transmitted through a string, rope, cable, or wire when it is pulled tight on opposite ends. Contact Force: Compression Force - Force is exerted by a compressed or stretched spring upon any object attached to it. Contact Force: Friction Force - Force that serves to slow down or prevent the motion of an object. It is always parallel to the surface in contact and opposite in direction. Contact Force: Air Resistance - Force that acts upon objects as they travel through the air. The source of resistance is due to the cumulative interaction with gas molecules. Air Contact Force: Applied Force - A force applied to an object by a person or by another object Non-Contact Forces Non-Contact Force: Gravitational Force - Also known as weight. A force that is directed downward towards the center of the Earth. Gravitational constant: 9.8 m/s² Weight as a force - Since weight is a force, this is the following equation: W = mg Non-Contact Force: Electrostatic Force - Force in electrical charges - 2 electrically charged objects (charged bodies) - Attractive or repulsive forces between Non-Contact Force: Magnetic Force - Attractive or repulsive forces between 2 electrically charged objects (magnetized objects) Balanced & Unbalanced Force Balanced Forces - Forces acting on an object are equal in magnitude and in opposite directions Motion: stationary Net force: 0 net force -300 N + 300 N = 0 !!! Unbalanced Forces - Forces acting on an object are not equal in magnitude and in opposite directions ‘ Motion: moving Net force: non-zero net force Laws of Motion Law of Inertia Inertia - Tendency of an object to keep doing what it is already doing - Stationary object tends to remain at rest Law of Inertia - An object at rest will remain at rest - An object in motion will remain in motion - For as long as there is not an external net force acting on it Inertia is not a force!! It is a property of an object. Inertia also depends on the mass of an object. The greater the mass; the higher the inertia; the harder for the object to change position Inertia is also related to equilibrium. Equilibrium - all forces acting on an object balances each other out - Net force (resultant force) is equal to zero Law of Acceleration - If a net force is acting on an object, it will accelerate in the direction of the net force. - Two factors affecting acceleration: force and mass The greater the force applied, the higher the acceleration (at constant mass) The greater the mass of the object, the lower the acceleration (at constant force applied) An applied force causes the body to accelerate in the direction of the force. Fnet = ma 1. How much force is needed to move a 20-kg sack of rice at an acceleration of 5 m/s? Given: required: Fnet = ma Mass = 20 kg solution: Acceleration = 5 m/s² (20 kg)(5 m/s²) = 100 kgm/s² Final answer = 100N 2. What acceleration will result when a 10-N force is applied on a 5kg stack of boots? Given: required: acceleration = Fnet/m Fnet = 10 N/10 kgm/s² solution: Mass = 5 kg 10 kgm/s² ÷ 5 kg Final answer = 2 m/s² Law of Interaction 1. It always acts on different objects (object A, object B) 2. It always involves 2 forces; one applied by A on B 3. Forces occur simultaneously 4. These 2 forces are equal in magnitude 5. These 2 forces are in opposite directions “For every action, there is an equal and opposite reaction” Rocket pulls earth up Exhaust gases push rocket up = thrust Earth pulls rocket down engine pushes exhaust gases down Uniform Circular Motion Uniform Circular Motion An unbalanced force causes a body to accelerate, so, a body in circular motion undergoes centripetal acceleration caused by an unbalanced force called centripetal force - Path: arc or a circle - Speed and velocity - the speed is constant, the velocity (direction) is changing - Acceleration - constant magnitude - constantly changing direction - perpendicular to velocity and force Centripetal force - Closer to the center Centrifugal force - Farther to the center Centrifugal force is a fictitious force. Being pulled outward is due to inertia which resists the force that pushes the body toward the center of the circular path. The frictional force that exists between the car’s tires and the road keeps the car in its circular motion Work, Power, and Energy Work - A product of an applied force to move an object away from its original position in the direction of the force. - It is a scalar depending on two vectors - The product of force and displacement - Expressed in joules and ergs Work is done only when a force causes a body to move in the same or opposite as the force applied on it. It can be defined by: W=Fxd or simply W = Fd where: Variables Symbol Units force F N Displacement d m Work W J/Nm F —----------> Value: positive d —----------> Direction: F and d is same direction and parallel F —----------> Value: negative D ←—-------- direction: F and d is opposite direction and parallel 1. Julio pushed a wall in his home with 20N of force. The wall did not move, and Julio became exhausted. Is there work done on the wall? Given: required: W = ? d=0 equation: W = fd F = 20 N solution: W = 20 x 0 = 0 Final: W = 0 J (no lol) 2. Calculate the work done on a box that was moved to a distance with a distance of 2.5 m with an 80-N force. Given: required: W = ? F = 80 N equation: W = fd d = 2.5 m solution: 80 x 2.5 = 200 Final: 200 J Power - Rate of doing work - Can be defined as P = W/t variables symbol units power P W (watt) work W Joules time t seconds Energy - In a closed system, energy is neither created nor destroyed, it only changes in form. Energy is the capacity of work (sorry for ugly drawing. Even tho its ugly u cant say it okay!!) The two forms of mechanical energy are Potential energy and Kinetic energy. Mechanical energy Kinetic Energy - Energy of Motion - An object at rest has zero KE where: Variables Symbol Units Kinetic energy KE J Mass m Kg velocity V m/s 1. Calculate the kinetic energy of a 370 kg push cart moving at 6.4 m/s Given: V = 6.4 m/s required: KE = ? m = 370 kg equation: KE = 1/2mv^2 Solution: KE = 1/2 (370 kg)(6.4 m/s)² Answer: 7,577.6 J 2. What is the kinetic energy of a 2.9 kg bowling ball moving at 20 m/s? Given: V = 20 m/s required: KE = ? m = 2.9 kg equation: KE = 1/2mv^2 Solution: KE = 1/2 (2.9 kg)(20 m/s)² Answer: 580 J Work-Energy Principle - Also known as the work-energy theorem - Relationship of the amount of work done on an object with the change in its energy - The total work done on an object is equal to the change in its kinetic energy. W = KE Based on the work-energy theorem, the amount of work done by a force on an object is equal to the change in its kinetic energy. therefore: work = Fd = KE work = (Fweight)(d) = KE work = mgd = ke Potential Energy - Energy of position (stored energy) - An object at rest has zero KE. Gravitational Potential energy - Energy stored due to vertical height - Falling objects Elastic Potential energy - Stored in elastic materials - Stretching and compression of objects Gravitational Potential Energy - Energy stored due to vertical height  - Falling objects - Any object which has GPE can do work when allowed to fall. Variables symbol units GPE GPE J M m kg Acc. due to gravity a/g m/s² height h m 1. Hidilyn Diaz lifted a 224-kg barbell through a height of 1.7m during the 2021 Olympics. By how much is she changing the GPE of the barbell? Given: m = 224 kg req: GPE h = 1.7 m equation: GPE = mgh solution: GPE = (1.7m)(9.8 m/s²)(224 kg) answer: 1,575 J Work Energy principle Any object which has GPE can do work when allowed to fall. Therefore, Work = GPE = mgh Elastic Potential Energy Variables Symbol units EPE EPE J Spring constant k N/m Change in length x m 1. A spring constant of 5 N/m and is initially 6-cm long. What is its EPE when its stretched to 8-cm? Given: x = 0.02m/2cm req: EPE = ? k = 5 N/m EPE = 1/2kx² Solution: EPE = 1/2 (5)(0.02)² Answer: 0.001J 2. A spring with a spring constant of 150 N/m is compressed by 0.3-m. How much EPE is stored in the spring? Given: x = 0.3m req: EPE = ? k = 150 N/m EPE = 1/2kx² Solution: EPE = 1/2 (150)(0.3)² Answer: 6.75 J Total Mechanical Energy Mechanical energy - Result of an object’s motion (KE) and/or stored energy (PE) TME = KE + PE Mechanical energy can be converted between KE and PE. Law of Conservation of Energy - Energy can neither be created nor destroyed. It can only be converted from one form to another. Therefore, the initial TME = final TME (always) Calculating TME Assuming there is no friction, determine the missing values of the pendulum. (pretend there's a pendulum lol) Point GPE KE TME A 500 J 0J 500 J B 0J 500 J 500 J C 450 J 50 J 500 J 1. Mark is in a roller coaster car travelling at a speed of 2.20 m/s at a height of 15-m. If his mass is 78.85 kg, what is his TME? given: h = 15m required: TME = ? V = 2.20 m/s equation: TME = (1/2mv²)(mgh) M = 78.85 kg solution: TME = (½)(78.85 KG)(2.20 m/s)² + (78.86kg)(9.8m/s²)(15 m) Answer: 11,781.77 J Waves Sound Waves Waves - A disturbance that travels through space and time, and that transfers energy Parts of Waves Wavelengths - distance between two crests Frequency - no. of waves that pass over a period of time Sound - A wave that carries vibrational (mechanical) energy through a medium, to a receiver Medium - An object or substance that allows the transfer of energy. - Examples of mediums are solids, liquids, gases Transmission of Sound - The particles of the medium transmit the sound energy by vibrating in their position, colliding with their neighboring particles and exchanging kinetic energy with them. Speed of Sound Air - 330 m/s Water - 1400 m/s Liquid particles are not very elastic or dense. Gases are the poorest sound transmitters. Temperature - The measure of the average kinetic energy of the particles in an object Speed of Sound and Temperature - How fast sound moves depends on the temperature of the medium. - As heat energy increases, kinetic energy of particles increase - Sound waves travel faster in warm mediums than in cool mediums. Properties of Sound Waves - Sound waves exhibit the general properties of waves, which includes reflection, refraction, diffraction, and interference, when they interact with matter. Reflection of Sound - The bouncing back of sound (echoing) when it hits a surface - The echo will be of the same pitch, but will be fainter because iti has lost energy as it travels through air Refraction of Sound - The bending of sound waves - Sound waves bend when they travel through air at uneven temperatures. Day: sound goes upwards because air in the ground is warmer. Night: sound goes downwards because air in the ground is colder. Diffraction of Sound - The bending of sound waves around obstacles and through small openings - The sounds you hear are fainter because they travel farther, they lose energy and become weaker Interference of Sound - When two or more sound waves from different sources are present at the same time, they interact with each other to produce a new wave Constructive interference - When two waves combine to produce a wave of greater amplitude (i.e: baby crying and mother yelling) Destructive Interference - When two waves combine to produce an amplitude smaller than the original amplitude (i.e: singers voice and instrumental) Light Waves Light - A type of electromagnetic wave that does not require a medium to propagate Properties of Sound Waves Reflection of Light - The bouncing of light when it hits a surface or boundary of another medium - Depends on the texture of surface (Rough/smooth) Specular reflection - light reflects at the same angle as it hit the surface Diffuse reflection - light reflects at the different angles and we see different textures and colors Refraction of Light - High density medium will slow down the speed of light Dispersion of Light - Light is separated into different colors due to varying degrees of refraction Red is bent the least because it has the longest wavelength and lowest frequency, and violet is bent the most because it has the shortest wavelength and highest frequency. Diffraction of Light - The bending of light around obstacles or through tiny openings. - This phenomenon causes the formation of shadows. Interference of Light - Two or more light waves combining and forming a resultant wave that has a lower, equal, or a higher amplitude. (i.e: dark + dark = black) Colors of Light Visible spectrum shows us the colors that we can see using our eyes Primary colors - Red blue green Secondary - Magenta cyan yellow R + G + B = white Bioluminescence - Is a biochemical emission of light by living organisms. Good luck