Investigate the relationship between the amount of force applied and the mass of the object to the amount of change in the object’s motion.

SCIENCE 8: FORCES

1. FORCES

2. After going through this module, you are expected to: Investigate the relationship between the amount of force applied and the mass of the object to the amount of change in the object’s motion. (Week 1 S8FE-Ia-15)

3. OBJECTIVES: 1. Identify what forces are acting on an object at rest 2. Explain the effect of balanced and unbalanced forces on the state of motion of an object. 3. Appreciate the importance of forces acting on objects.

4. Multiple Choice: Read each statement carefully and write only the letter of the correct answer. A book is at rest on top of a table. Which of the following is correct? There is no force acting on the book. B. The book has no inertia. C. There is no force acting on the table. D. The book is in equilibrium.

5. 2. Which of the following situations involves friction? A bicycle rolling down a hill B. A baseball player sliding into 2nd base C. A diver falling through the air to a pool D. All of the above experience some friction.

6. 3. What is gravity? Newton’s first law B. The force that objects exert on each other because of their masses C The downward pull on the Earth D. The friction that an object has put on it

7. 4. Which is the best example of gravity? A car hits a tree, and its motion stops B. A breeze blows, and a sailboat moves C. A book is pushed, and it moves across the table D. A person drops a ball, and it falls to the ground

8. 5. How does Earth ‘s gravity affect objects near Earth? A. It pushes them away. B. It pulls them in C. It makes them larger. D. It makes them move faster.

9. D D C D B

10. the change in position of an object . It is a vector quantity and has a direction and magnitude. DISPLACEMENT- VELOCITY - defines the direction of the movement of the body or the object. ACCELERATION - the rate of change of velocity .

11.  MAGNITUDE – refers to the size or strength of the force. It is commonly expressed in Newton (N) for Meter-Kilogram-Second (MKS) system, Dyne ( dyn ) for Centimeter–Gram–Second (CGS) system and pounds ( lbs ) for Foot– Pound–Second (FPS) system. In the International System of Units (SI), Newton is commonly used which is named after Sir Isaac Newton, an English physicist and mathematician.  DIRECTION – points to where the object goes. The direction of the arrowhead indicates the direction of the force. The length of the arrow represents the amount of force (relative magnitude).  POINT OF APPLICATION – the location of where the force is applied.  LINE OF ACTION – is the straight line passing through the point of application and is parallel to the direction of force.

12. ACTIVITY 1: AGREE OR DISAGREE Direction: Read the following statement. Do you agree or disagree? Explain your stand. Force is needed to stop an object. 2. Force always results to motion. 3. Force can act even at a distance. 4. Objects have the tendency to remain at rest. 5. Objects have the tendency to resist change.

13. ACTIVITY 1. EFFECT OF FORCE ON A BALL Direction: Examine the ball on top of the table. Answer the questions.

14. There are two types of force, namely: CONTACT FORCES – forces where objects touch or contact with each other.

15. Examples of contact forces: 1. APPLIED – a force given to a person or object by another person or object. Its symbol is F depending on who or what applies force to the object. If a boy applies a force to a wall, we denote it with FBOY. Refer to the figure below.

16. 2. FRICTION – is the force acting against or opposite an object in contact with which makes the movement of the object slow down. Friction always opposes the motion of an object. Its symbol is written as Ff. Air resistance denoted by FAIR is an example of frictional force of the air against a flying kite, airplanes, parachutes or those in skydiving sports. For free-falling objects, this force is always considered negligible, meaning the magnitude is unnoticeable.

17. 3. NORMAL – is the force that acts perpendicular to the surface of the object in contact with. Its symbol is FN.

18. 4. TENSION – is the force applied to string, rope, chain or cable. Its symbol is T. Figure 11. Tensional force or simply tension (T) that acts on the rope of a hanging ball

19. NON-CONTACT FORCES – Forces where objects do not touch or contact with each other. -These forces act over a zone or area called field.

20. Examples of non-contact forces: 1 . GRAVITATIONAL ( Fg ) – is the force of attraction between two objects Figure 12. Gravitational force between the Earth and the Moon.

21. Figure 13. Illustration of the weight of a book (W BOOK ) on the table with normal force (F N )

22. 2. MAGNETIC – are forces exerted on a field of attraction or repulsion as in the case of magnets and other magnetic materials. Figure 14. Opposite poles attract Like poles repel

23. BALANCED FORCES

24. Forces that are equal in magnitude but opposite in direction. - Balanced forces do not cause a change in motion. When balanced forces act on an object at rest, the object will not move. BALANCED FORCES

25. Figure 15. A representation of balanced forces in a tug-of-war game

26. UNBALANCED FORCES

27. UNBALANCED FORCES Are forces that cause a change in the motion of an object - Unbalanced forces are not equal and in opposite direction.

28. Figure 16. A representation of unbalanced force in a tug-of-war game

29. NET OR RESULTANT FORCE - is the sum of all forces acting on an object. Two or more forces in the same line of action exerted on an object are balanced if their effects cancel each other.

30. ACTIVITY 2. FORCES ON OBJECTS AT REST Objective: After accomplishing this activity, you should be able to identify what forces are acting on an object at rest.

31. Directions: A. Look and study the picture below. Figure 17 shows a block of wood lying on a table.

32. Questions: Is the block of wood at rest or in motion? 2. Refer to the figure below. Draw the forces acting on the block of wood. Use the dot as the origin of the forces.

33. ACTIVITY 3. BALANCE OF FORCES

34. Procedure: Examine the pictures below: FA - applied force on the rope by Team A FN – force exerted by the floor on the ball FB - applied force on the rope by Team B Fg - force exerted by the Earth on the ball Ff - opposite force in the direction of the Fapplied – applied force on the ball motion or frictional force Figure 19. A ball pushed on the floor Figure 18. Balanced forces in a tug-of-war.

35. 1. If two groups in the game are exerting equal and opposite forces on the rope, will the rope move? _________________________________________________________ 2. In the same condition, what happens to the net force acting on the rope? _________________________________________________________ 3. What are the forces present on the rope? ________________________________________________________ 4. Refer to Figure 19. If you place a ball on the floor then push it gently to one side, observe the motion of the ball as it rolls down the floor. a. What makes the ball stop rolling after sometime? ______________________________________________________ b . What are the forces that act on the ball? ______________________________________________________

36. ACTIVITY 3. UNBALANCED FORCES

37. Procedure: Examine the pictures below. Fig 20. Unbalanced forces in a tug-of-war Fig 21. A chandelier hangs on a chain.

38. 1. If two groups in the game are exerting unequal and opposite forces on the ground, will the rope move? ______________________________________________________________ 2. Will the net force be equal to zero? ______________________________________________________________ 3. To what direction does the rope move? ______________________________________________________________

39. Procedure: Examine the pictures below. Fig 21. A chandelier hangs on a chain.

40. For question numbers 4 – 6, refer to figure 21. 4. Are the forces acting on the chandelier unbalanced? ______________________________________________________________ 5. What force can cause the chandelier to fall? ______________________________________________________________ 6. What type of force is your answer in number 4? ______________________________________________________________

41. Fill in the blanks with correct word/s. Write your answers on a separate sheet of paper. 1. Any push or pull is called ________________. 2. ________________ refers to the size or strength of the force while ________________ points to where the object goes. The direction of the arrowhead indicates the direction of the force. The length of the arrow represents the amount of force (relative magnitude). 3. There are two types of forces, namely ________________ and ________________. 4. Applied, friction, normal and tensional forces are examples of ________________ forces. 5. Gravitational and magnetic forces are examples of ________________ forces. 6. ________________ are forces that are equal in magnitude but opposite in direction. 7. ________________ are forces that cause a change in the motion of an object. 8. The sum of all forces acting in an object is called ________________. 9. If the forces in an object are balanced, the net force is ________________. 10. If the forces in an object are unbalanced, the net force is ________________.

42. Fill in the blanks with correct word/s. Write your answers on a separate sheet of paper. 1. Any push or pull is called ________________. 2. ________________ refers to the size or strength of the force while ________________ points to where the object goes. The direction of the arrowhead indicates the direction of the force. The length of the arrow represents the amount of force (relative magnitude). 3. There are two types of forces, namely ________________ and ________________. 4. Applied, friction, normal and tensional forces are examples of ________________ forces. 5. Gravitational and magnetic forces are examples of ________________ forces. 6. ________________ are forces that are equal in magnitude but opposite in direction. 7. ________________ are forces that cause a change in the motion of an object. 8. The sum of all forces acting in an object is called ________________. 9. If the forces in an object are balanced, the net force is ________________. 10. If the forces in an object are unbalanced, the net force is ________________. FORCE MAGNITUDE DIRECTION CONTACT NON-CONTACT CONTACT NON-CONTACT BALANCED UNBALANCED NET OR RESULTANT ZERO