Force, Motion And Energy

FORCE, MOTION AND ENERGY 4.1 | SCIENCE | QUARTER 04 2023 Asian Philosophers were interested in defining and describing the motion. INTERNATIONAL SYSTEM OF UNITS (SI) - the standard unit of force is ● the N 1N = 1kg x cm/s^2 Aristotle stated to keep an object moving a force should be continuously applied on it, but this something. statement is missing ● FORCE ● ● ● ● ● Its either push or pull Push - it is directed away from that which exerted it. Pull - exerted effort towards you Expressed in a unit called Newton (N) to honor the British physicist Isaac Newton REPRESENTING FORCES THROUGH DIAGRAM ● Inanimate objects aso exert forces called “pull of gravity” or the “force of gravity” ● NORMAL FORCE - is a pushing force which always acts perpendicular to the surface it exerts. ● TENSION - is a kind of pulling force exerted on a non-rigid object such as a rope, string or chain MEASURING FORCES SCALES - used to measure forces ● You may not encounter many scales that measure weight in newton ● Units of mass (kilograms or grams) ● Older, non-standard unit - pound (lb) CENTIMETRE-GRAM-SECOND SYSTEM OF UNITS (CGS) - Force is measured in a unit called dyne. It is never abbreviated. 1 dyne = 1g x m/s^2 ● Use one-way arrow to represent a force on a paper The length of the arrow itself is an indication of the strength of the force Should always have at one end an arrowhead that points in the direction of the force. Vector Quantity has a magnitude and direction. CONTACT AND NONCONTACT FORCES Contact ● ● Contact is needed for the force to act on objects Include normal force, tension compression, and friction Noncontact Forces ● Also called action-at-a-distance forces Reviewer by: Khasandra Chloe S. Serrano 1 FORCE, MOTION AND ENERGY 4.1 | SCIENCE | QUARTER 04 2023 ● ● Include gravitational forces Between charged particles called ● Electrostatic Forces. Magnets also exert noncontact forces between them. 1. 2. Inertia is the tendency of an object to resist any change in its state of motion. Inertia is not a force. It is the property of an object. 3. Inertia is measured by an object’s mass. ● Exist when all the forces acting on an object balance each other out. Sum of all forces acting on the object is zero. THE LAWS OF MOTION Sir Isaac Newton ● Summarize the reasons why objects move, stop or keep moving ● The three Laws of Motion ● ● ● Law of Inertia Law of Acceleration Law of Interaction Dynamics (Dynamics of Motion) ● Ascertains the reasons why objects move the way they do, and why some objects move fast while some move slowly EQUILIBRIUM ● FINDING THE NET FORCE ● ● ● LAW OF INERTIA - Also known as the law of equilibrium Centered on the concepts of inertia and equilibrium Inertia ● Tendency of an object to keep doing what it is already doing The net force is also known as resultant force, and needs to be zero. Added using vector addition Positive signs for forces that are to the right and negative signs for forces which are to the left. Example: 1. Fnet = 5N + 10n = 15N (not equilibrium) 2. Fnet = 5N + (-5N) = 0 (equilibrium) (Galileo) If something pushes to start moving or to slow it down or speed it up, the object puts up “resistance” Resistance is applied because of Inertia. Important things to remember about Inertia: EQUILIBRANT - - A nonzero net force acting on an object is balanced by a single force. It causes the object to be in equilibrium Example: Reviewer by: Khasandra Chloe S. Serrano 2 FORCE, MOTION AND ENERGY 4.1 | SCIENCE | QUARTER 04 2023 1. 5N, -5N Fnet = 5N + (-5N) = 0 2. 5N, 7.5N Fnet = 7.5N + (-5N) = 2.5 N to the left 2.5 + 5 = 7.5 LAW OF ACCELERATION ● When the net force acting on an object is not zero the object accelerates. This change can either be a change in speed, a change in direction, or a change in both speed and direction. m = 5kg m2 = 10kg a1 = ? a2 = ? Solution: Fnet = ma Fnet = ma m m Derived formula. To find the acceleration we must have to divide the mass and acceleration to mass and so in Net force. Then we must cancel out the mass on the right side. Formula: ACCELERATION - ● Measure how fast the velocity of an object changes. a= The magnitude of the acceleration is directly proportional to the net force and inversely proportional to the object mass. Fnet = 10n Note: First part, Net force causes acceleration and defines the direction of the acceleration. Relates the quantity of Fnet m m = 5 kg 10N 5 kg Lets cancel out the kg and we must use the formula of SI, 1N = kg x m/s^2 the net force to that of the acceleration. ★ Acceleration increases when the net force increases. Yet,mass plays into the equation. Example: Fnet = ma Given: Fnet = 10N 10 kg x m/s^2 5 kg We must cancel out kg and 10 divided by 5 is 2, so our answer is.. = 2 m/s^2 Reviewer by: Khasandra Chloe S. Serrano 3 FORCE, MOTION AND ENERGY 4.1 | SCIENCE | QUARTER 04 2023 MASS AND WEIGHT Show how much Inertia an object has. The forces that earth exerts object or near it Not a force A force Remains the same regardless of loc. Varies in magnitude from place to place. Standard SI unit Newtons or dynes (dyn) kingdom (kg) Weight can be calculated from the mass using an equation similar to F = ma LAW OF INTERACTION ● ● W = mg When: ● ● ● Weight of the object is W Mass of the object is m g is the acceleration due to gravity at the specific location on Earth, g = 9.8 m/s^2 = 980 cm/s^2 directed downward. Example: W = mg w=? gm = 1.62 m/s^2 ge = 9.8 m/s^2 Let’s proceed to Earth gravitational. We must use multiplication. w = (100 kg) (9.8 m/s^2) = 980 kg x m/s^2 = 980 N Same formula for the second one. Have you ever awakened to see that your pillowcase has left marks on your face? This is a reminder that when you touch something, it touches you back. The weight (a force) of your head is directed toward the pillow; the pillow has to apply an upward force on you at the same time. This manifests Newton’s third law of motion, also known as Law of Interaction. The Law of Interaction always involves two objects, such as your face and the pillowcase. The Law states: When a body A exerts force on a body B, B exerts an equal but opposite force on A. FRICTION ● ● ● Friction is a contact force that serves to slow down a moving object or prevent motion altogether. Friction is always parallel to the surface in contact and if the object is moving, it is the opposite direction of motion. Friction may occur between solid objects, It may also exist between a solid and a fluid. The two kinds of friction are: Static Friction - Prevents two objects from sliding against each other. Reviewer by: Khasandra Chloe S. Serrano 4 FORCE, MOTION AND ENERGY 4.1 | SCIENCE | QUARTER 04 2023 Kinetic Friction - Exist when objects slide against each other, like in the case of moving machine parts. Beneficial Effects of Friction: 1. Use materials that are naturally rough. Sandpaper comes in various “grits” or roughness. Tires come in various treads, making some tires better than others for wet conditions. 2. Increase the pressure between the surfaces. When cleaning off tough stains from a surface, it is best to press down harder as you scrub. The added pressure increases the friction between the surfaces. In places where heavy snowfall occurs people drive around with a load of snow on top of their vehicle, increasing the vehicle’s weight and therefore the friction. 3. Use the right combination of materials. Friction does not just depend on one of the two surfaces, but on the pair of surfaces. Rubber on concrete produces more friction than rubber on glass, for example. UNDESIRABLE EFFECTS OF FRICTION 1. Friction causes the soles of our shoes to wear out. 2. In industry, machine parts grind against one another, generating heat and resulting in tremendous losses of energy. Machine parts have to be replaced due to wear as a result of this grinding. 1. 2. 3. WAYS TO REDUCE FRICTION Use a lubricant. A lubricant is any substance that spreads over the minute grooves and cracks on solid surfaces, making the surfaces more even. Reduce the contact between surfaces. This is the opposite of pressuring surfaces harder to increase friction. This is how some inter island ferries increase their speed over water. Use bearings. Ball bearings are used to reduce or eliminate sliding friction between the wheel and the axle. As the wheel turns, so do all the bearings. There is no sliding, only rolling. With some added grease, rolling friction is further reduced. CIRCULAR MOTION Circular motion is more common than one might think at first. We see it in the potter’s wheels, Ferris wheel, and merry-go-round. Uniform Circular Motion (UCM) ● The simplest type of circular motion. The characteristics of this type of motion are the ff: 1. The path of the objects is an arc or a circle. In other words, the object may move through a portion of a circle. 2. The speed (magnitude of the velocity) is constant during the motion. 3. The direction of motion changes Reviewer by: Khasandra Chloe S. Serrano 5 FORCE, MOTION AND ENERGY 4.1 | SCIENCE | QUARTER 04 2023 4. moment by moment. The acceleration of the object is constant and is always perpendicular to the velocity. It is directed toward the center along negotiates a 500.0 m radius curve at 25.00 m/s. We know that: Fc = mv^2 the radius. r Thus, The net force that pulls the object toward the center of the circle is referred to as the centripetal force of Fc. Example: A car negotiating a turn needs the friction between the tires and the road to provide centripetal force. Fc = mv^2 r = (900.0 kg) (25.00 m/s)^2 (500.0 m) = 1125 N Moving In Many Circles Uniform circular motion governed by Newton’s second law in which the net force is replaced by the centripetal force. In this case, The acceleration is referred to as the centripetal acceleration because it also points inward. It is related to centripetal force by equation: Fc = mac Period - the time within which an orbiting body completes its movement in a circle. The centripetal acceleration is related to the speed of the object around the circle by the formula: Frequency - the reciprocal of period - denoted as f - It is given in the unit “per second” or /s. - also called Hertz (Hz) named after the German scientist Heinrich Hertz. ac = v^2 r Thus, we can also calculate the centripetal force using: Fc = mv^2 r Example: a) Calculate the centripetal force exerted on a 900.0 kg car that For example, the period of the Earth’s The revolution around the Sun is one year. Period T may be given in seconds (s) or any other unit of time. In symbol, period and frequency are related by the equation: f=1 T For an object with a given frequency or period moving in a circle of radius r, we Reviewer by: Khasandra Chloe S. Serrano 6 FORCE, MOTION AND ENERGY 4.1 | SCIENCE | QUARTER 04 2023 can determine its speed v (also known as the orbital speed) around the circle. v = 2πa T Reviewer by: Khasandra Chloe S. Serrano 7