8 Science Quarter 1 – Module 3: Potential Energy and Kinetic Energy
Science – Grade 8 Alternative Delivery Mode Quarter 1 – Module 3: Potential Energy and Kinetic Energy First Edition, 2020 Republic Act 8293, section 176 states that: No copyright shall subsist in any work of the Government of the Philippines. However, prior approval of the government agency or office wherein the work is created shall be necessary for exploitation of such work for profit. Such agency or office may, among other things, impose as a condition the payment of royalties. Borrowed materials (i.e., songs, stories, poems, pictures, photos, brand names, trademarks, etc.) included in this module are owned by their respective copyright holders. Every effort has been exerted to locate and seek permission to use these materials from their respective copyright owners. The publisher and authors do not represent nor claim ownership over them. Published by the Department of Education Secretary: Leonor Magtolis Briones Undersecretary: Diosdado M. San Antonio Development Team of the Module Writers: Cheri Madleen T. Samaco Editors: Nonita C. Patalinghug, Rhoda M. Delos Santos Reviewers: Bernabe L. Linog, Relyn D. Raza Illustrator: Rosa Mia L. Pontillo Layout Artist: Celeste Faith R. Almanon, Jay S. Ayap Management Team: Francis Cesar B. Bringas Isidro M. Biol, Jr. Maripaz F. Magno Josephine Chonie M. Obseñares Gregoria T. Su Marvilyn C. Francia Nonita C. Patalinghug Printed in the Philippines by ________________________ Department of Education – Caraga Region Office Address: Teacher Development Center J.P. Rosales Avenue, Butuan City, Philippines 8600 Telefax: (085)342-8207/(085)342-5969 E-mail Address: [email protected]
What I Need to Know This module was designed and written with you in mind. It is here to help you master potential and kinetic energy. The scope of this module permits it to be used in many different learning situations. The language used recognizes the diverse vocabulary level of students. The lessons are arranged to follow the standard sequence of the course. But the order in which you read them can be changed to correspond with the textbook you are now using. This module contains: Lesson 1 – Potential Energy and Kinetic Energy After going through this module, you are expected to: 1. Identify and explain the factors that affect potential and kinetic energy. (MELC Week 2-3) 1
What I Know Directions. Choose the letter of the correct answer. Write your answers on a separate sheet of paper. 1. An object from a certain height falls freely. Which of the following happens to PE and KE when the object is half on its way down? A. loses PE and gains KE B. gains PE and loses KE C. loses both PE and KE D. gains both PE and KE 2. How do you compare the PE of the moving object at the highest point compared to its KE? A.PE is greater than KE B. PE is equal to KE C. PE is lesser than KE D.KE is greater than PE 3. Which of the following quantities has the greatest influence on the amount of kinetic energy of a car while traveling on a highway? A. mass B. size C. speed D. weight 4. Which of the following pair of quantities are the factors that affect kinetic energy? A. force and distance B. mass and height C. mass and speed D. time and height 2
For Questions 5-6. Refer to the illustration below. 5. Which point has increasing kinetic energy? A. Point C B. Point B C. Point A D. Point A & C 6. Which point has the greatest potential energy? A. Point A B. Point B C. Point C D. Point A & C 7. Which of the following statements is TRUE about potential energy? A. It is dependent on the speed of an object. B. It does not depend on the mass of the object. C. It does not depend on the strength of gravity. D. It is affected by the mass and location of an object with respect to the ground. 8. Which of the following does not affect the amount of potential energy of an object? A. mass B. speed C. height or location D. strength of gravity 3
9. The following applies the concept of potential energy EXCEPT: A. water in a dam B. a person playing the guitar C. a rock sitting at the edge of a cliff D. tree branches high up in a tree 10. What happens to the kinetic energy of an object if its speed is doubled? A. twice as much B. thrice as much C. increases four times D. decreases four times 4
Potential Energy and Lesson 1 Kinetic Energy The word energy is used very often in our daily life. In science, there are many forms of energy however; this module shall only focus on Potential Energy and Kinetic Energy. What’s In Energy: The ability to do work Let us consider the following situations: A fast-moving softball hit a stationary, open door which caused it to move. An object lifted to a certain height using a rope, elevated the object from the ground. A hammer struck on a nail that was placed on a piece of wood, pushed the nail into the wood. A toy car’s key was twisted, placed on the floor and started to move. In all these situations, forces acting on the objects are doing work. An object requires energy to do work. Consider two objects A and B that are about to interact with each other. When object A is pushed, an applied force is doing work on it. Object A possesses kinetic energy while moving towards a stationary object B. In this situation, object A loses energy while object B gains energy. When this happens, energy is transferred from object A to object B. This indicates that any object that has energy can do work. Energy is the ability or capacity to do work. Its unit is the same as the unit of work, expressed in joule (J) in the SI system. One (1) J is the energy needed to accomplish one (1) joule of work. A larger unit of energy called kilojoule (kJ) is sometimes used. One (1) kJ is equal to1000 J. 5
What’s New Activity 1. Energy Crossword Puzzle Objective: Familiarize the words that are associated to the concept of energy. Directions. Complete the crossword puzzle below. Across: Down: 1. The product of force and 2. _________ energy is associated displacement is __________. with motion. 4. __________ is the unit of 3. The total __________ energy is energy in SI system. the sum of kinetic and 6. __________ energy is stored potential energy. due to the object’s position. 5. The ability to do work is __________. Notes to the Teacher Provide extra copies of this page for students’ use. 6
What is It Potential Energy In the previous lesson, you were asked if the man lifting the box is doing work on it. Figure 1. A man lifting a box Source: Pia C. Campo, et. Al., A man lifting a box, Science 8 Learner’s Material, Philippines, FEP Printing Corporation, 2016 Which or who is doing work in Figure 1? Is it the table, the box, or the man? Yes, you are correct! The man is doing work on the box. Specifically, the force he applied while lifting is doing work on the box. What is the direction of the force exerted by the man on the box? What is the direction of the motion of the box? Yes, both are directed upward. Work, as discussed earlier, is a way to transmit energy. Hence, when the man exerted force in lifting the box, he loses energy. Work is done on the box, and the box gains energy. You have learned that force of gravity is the force exerted by the Earth on all things. It is always directed downward or towards the center of the Earth. Consequently, when an object is raised from the Earth, the force exerted in lifting the object is equal to its weight, F = Weight = mg The work done in lifting the object is: W = Fd where, the displacement (d) is the height (h) the object is raised. Thus, the work done in lifting the object against the gravitational force is given by W=mgh 7
The work performed in lifting an object is equals to the potential energy the object gains. An object absorbs energy when lifted from the ground and when allowed to fall, it loses energy. The energy that the body gains or losses with respect to its position is called potential energy (PE) and is given by PE=mgh where: PE is the potential energy in joules (J); m is the object's mass in kilograms (kg); g is the acceleration due to gravity which is 9.8 m/s²; and h is the height of the object from the reference point (e.g., ground) in meters (m). Kinetic Energy What is common in the following situations? A running athlete on the track, a flowing water on the ground, a falling coconut from its tree, a rolling rock on the seashore, and a soaring airplane into the air. They are all moving and are acted upon by forces. Any object that moves possesses energy and can do work. An object that moves quicker can do more work than an identical object that moves slowly. How much energy does a moving object possess? We say that the kinetic energy of an object moving at a certain speed is equal to the work done to make it acquire that speed. The energy of a moving object is called energy of motion or kinetic energy (KE). The word kinetic comes from the Greek word kinetikos which means moving. Kinetic energy measures the amount of work the object can do because of its motion. This can be computed using the formula: KE = ½ mv² where: KE is the kinetic energy in joule (J), m is the object's mass in kilogram (kg), and v is the object's speed in meter per second (m/s). From the formula, the kinetic energy of an object depends on its mass and speed. What will happen to the KE of an object if its mass is doubled but the speed remains the same? The KE of an object is also doubled. How about if the speed is doubled but the mass remains the same? The KE of an object increases four times.This means that the greater the mass, the greater the kinetic energy; and the faster the speed the higher the kinetic energy as well. 8