Radio-based Instruction (RBI) | Science 8 - Law of Interaction [Week 2 - Module 2]

Good afternoon, Grade 8 Junior Scientists! I am Raymond T. Toralde, your radio teacher in Science. Now, we have so many things to explore with our topic. In the previous module, you have learned about the Law of Acceleration. What again is the Law of Acceleration? Great! The acceleration of an object is directly proportional to the magnitude of the net force acting on it and is inversely proportional to its mass. In this module, you will recognize that forces always come in pairs.

02:38 - Do you have any idea what is this Law of Motion that we are going to discuss? If you are thinking about Action and Reaction. You are right! Today, I am overwhelmed to be with you as we learn together our lesson in Law of Interaction. Do you have your module now? Are you ready with your pen and paper? Reminder science learners, please take utmost care of the modules given to you by your teachers, study well and read them with full understanding. To activate your prior knowledge of our lesson for today, let us have a pre-test. Please turn your module to page 3. (PAUSE) Together we will read each item carefully, then you will write the letter of the correct answer on your paper.

05:11 - Are you ready for it? Let’s begin! Number 1. A man pulls a large crate. According to Newton’s Third Law or law of interaction, how much force does the large crate exert on the man? A. Greater than the force exerted by the man. B. Lesser than the force exerted by the man C. Equal to the force exerted by the man D. Cannot be determined I will repeat the choices A. Greater than the force exerted by the man. B. Lesser than the force exerted by the man C. Equal to the force exerted by the man D. Cannot be determined Number 2.

06:18 - Refer to the picture in your module: In picture A, Eugene is pulling a rope that is attached to a wall. In picture B, Eugene is pulling a rope that is attached to an elephant. In each case, the force scale reads 500 Newton. What can you say about the force of Eugene? A. Eugene is pulling with more force when the rope is attached to the wall. B. Eugene is pulling with more force when the rope is attached to the elephant. C. Eugene exerted the same force in each case D. Eugene does not exert force in each case. I will repeat the options A. Eugene is pulling with more force when the rope is attached to the wall. B. Eugene is pulling with more force when the rope is attached to the elephant. C. Eugene exerted the same force in each case D. Eugene does not exert force in each case. Number 3. A player hits the ball with a bat.

07:35 - The action force is the impact force of the bat on the ball. What is the reaction force? A. the force the hand exerts in holding the bat B. the force of the ball exerts on the bat C. Weight of the ball D. Weight of the bat I will repeat the options A. the force the hand exerts in holding the bat B. the force of the ball exerts on the bat C. Weight of the ball D. Weight of the bat Number 4. Which of the following situations does not illustrate Newton’s third law of motion? A. Rowing a boat. B. A girl pushing a chair. C. A book on the top of the table. D. When the trigger of the gun is pulled. I will repeat the options A. Rowing a boat. B. A girl pushing a chair. C. A book on the top of the table. D. When the trigger of the gun is pulled. Number 5. Study figure A in your module, what law of motion explains the situation? A. Law of interaction, because for every action there is an equal but opposite reaction. B. Law of acceleration, because the acceleration is directly proportional to the net force acting on the body and inversely proportional to its mass. C.

Law of inertia, because bodies at rest will remain at rest and bodies in motion will 09:37 - continue moving at constant speed in straight path unless acted upon by a net force. D. Law of gravitation, because every particle in the universe attracts every other particle in the universe with a force that depends on the product of the two particles’ masses divided by the square of the distance between them. I will repeat the options A. Law of interaction, because for every action there is an equal but opposite reaction. B. Law of acceleration, because the acceleration is directly proportional to the net force acting on the body and inversely proportional to its mass. C. Law of inertia, because bodies at rest will remain at rest and bodies in motion will continue moving at constant speed in straight path unless acted upon by a net force. D.

Law of gravitation, because every particle in the universe attracts every other particle 10:40 - in the universe with a force that depends on the product of the two particles’ masses divided by the square of the distance between them. Are you done with the task? Let us check your answers. Number 1. How much force does the large crate exert on the man? C. Equal to the force exerted by the man You are Amazing! Number 2. What can you say about the force of Eugene? C. Eugene exerted the same force in each case Awesome! Number 3. What is the reaction force? B. the force of the ball exerts on the bat Marvelous! Number 4. Which of the situations does not illustrate Newton’s third law of motion? B. A girl pushing a chair. Terrific! Number 5. What law of motion explains the situation in Figure A? A. Law of interaction, because for every action there is an equal but opposite reaction. Superb! Did you get the answers…

12:22 - correctly? If YES Congratulations to those who got them. Don’t worry if you got a low score, this just means that there are more things than you can learn as we go on with our discussion on Law of Interaction. Are you ready? Great! On page 5, you will find the Learning Activities Section. Are you excited to learn more? Yes, good to know that! Have you experienced riding on a banca (fishing boat) in a river or a sea? If yes, I have questions for you: Number 1. What will you use for banca/boat to move? Number 2.

13:27 - What will you do to make the banca move forward? Number 3. What is the direction of the force you applied? Number 4. Is the direction of banca the same with the direction of your force? It is a one-of-a-kind experience to ride in a banca. Paddle is used to move the banca. If you paddle the water backward, you will go forward. If you paddle forward, then you will go backward. A force can be represented by means of an arrow. The length of an arrow represents the magnitude/strength of force, while its arrowhead represents the direction. All right! To improve your knowledge more, turn your module on Page 6 let us do an engaging activity. Take a look at the picture on the left side. It’s a rocket, right?! How does a rocket work? What do you think are the forces acting during a rocket launch? In the case of launching rocket, a rocket carries its fuel.

14:54 - Its engine turns the fuel into hot gas and pushes the gas out its back. The rocket’s action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force. The rocket exerts a downward force, and the reaction force pushes it upwards. The magnitude of the reaction is equal to the magnitude of the action but they are opposite in direction. There you go! But we’re not done yet.

15:37 - On Page 7, under the ‘Forces come in Pairs’ let us explore more about Law of Interaction. In this activity, you will identify situations showing action and reaction. You will also draw arrows to illustrate the forces that act between two objects, then explain how these forces act on each other. Number 1 is done for you! Number 2. Situation: Walking on the floor Does the situation show an action and reaction? Yes or No? Number 3. Situation: A person leaning on the wall.

Does the situation show an action and reaction? 16:29 - Yes or No? Number 4. Situation: A person steps off a boat Does the situation show an action and reaction? Yes or No? Number 5. Situation: A swimmer swimming forward Does the situation show an action and reaction? Yes or No? Number 6. Situation: A person sitting on a chair Does the situation show an action and reaction? Yes or No? In the last column, you will draw an arrow to show the direction of the forces acting between object if the situation shows an action and reaction. In the activity, you observed the similarities and differences between the interacting forces in terms of magnitude and direction.

17:38 - This relationship is stated in Newton’s third law of motion – Law of Interaction. Forces always occur in pairs, every time a force, or action, occurs, it causes a reaction. We can describe the reaction in terms of its strength or magnitude, and its direction. The magnitude of the action is equal to the magnitude of the reaction. The action and reaction forces are reciprocal (opposite) on an object. For example, in number 1 situation, if you throw a rock into the water, it’s going to create a ripple or splash. The force of the action and reaction always match up. While an action and its reaction are equal in magnitude, they are opposite in direction. The rock plunges down into the water, but the water splashes up. Both forces are always there whenever any force occurs.

18:38 - In the second situation, your foot pushes (action) and the ground pushes back (reaction). Likewise, as you lean on the wall, the wall exerts a force opposite and equal to the force you exert while leaning on the wall. In situation number 4, a person steps off a boat. As the person moves to the left, (that is the Action), when the boat moves back to the right (that is the Reaction). When you throw or shoot something forward, the recoil of the force pushes you backward.

19:17 - As the swimmer pushes against the water, the water pushes back on the swimmer and pushes her forward. When you push on an object, the object pushes back with an equal force. Think of a man sitting on a chair. The weight of the man exerts a downward force on the chair. This is the action force. The chair exerts an equal upward force on the man. This is the reaction force. Note that the two forces act on different objects. This action force acts on the chair, and the reaction force acts on the man. Every time a force acts on an object, it causes a reaction force in the opposite direction. The statement “For every action, there is an equal and opposite reaction.” means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object.

20:26 - The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs. So how was it? How did you find the discussion? If you think there is a need to go over the lesson again, yes, you can always go back before the module will be returned to your teacher. There are lots of real-life examples of the law of interaction. For instance, when playing volleyball, your arm exerts a force on the ball making it move forward.

21:13 - At the same time, volleyball exerts force on your arm which makes it painful. Now, it’s your turn to write down one real life example of law of interaction. Describe the action - reaction forces acting on the objects. I am giving you 5 minutes to write down your answer. Remember, law of interaction “For every action, there is an equal and opposite reaction. Did you enjoy our discussion today? (PAUSE) Great! How about the activities? (PAUSE). That is incredible! Now you see how the motions around us are related to Law of Interaction. Now, my dear students I hope you have learned a lot while enjoying the lesson. You still have other activities in the module. To further enhance your knowledge please continue answering the next task.

23:26 - A boy is pulled by a tractor and an elephant. Draw arrows to identify the chain of at least 6 pairs of action – reaction force pairs in the diagram as shown in your module. Should you have any difficulty, feel free to contact your teachers to help you. Important reminders, students: Now that we are experiencing a global health emergency brought by COVID-19 pandemic, it is just right to take utmost care of our health, practice self-care at the same time rekindle our commitment in taking good care of our studies. Thank you so much and ‘til next radio lesson. Goodbye! .