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Similar to Grade 8 -Quarter 1-PHYSICS 8-MELC 2.pptx (20)
Grade 8 -Quarter 1-PHYSICS 8-MELC 2.pptx
- 1. DELA PAZ NATIONAL HIGH SCHOOL Let us pray… Heavenly Father and Your Beloved Son Jesus Christ, We thank you for giving us another life, We thank you for another Beautiful day. As we go on through our lessons today, May you make us instruments to do good things. Please enlighten our minds, Give us the strength to participate in our subject today. Thank you for this opportunity to learn and serve others, and help me to always remember the Truth of Your Glory! In Jesus’ name. Amen
- 3. Which picture demonstrates motion?
- 4. MELC 2 Infer that when a body exerts a force on another, an equal amount of force is exerted back on it.
- 5. What is a force? • A force is a push or pull that causes an object to move, stop, or change direction • In physics a force is anything that makes an object accelerate • If an object is stationary, it won’t start moving without a force.
- 6. Force • Forces come in pairs • Forces have a magnitude and a direction • Force is a vector quantity 5N, north (up) Magnitude: 5N Direction: north (up)
- 7. Force Measurement and Units • SI unit for force is the Newton • A Newton is a force that causes a 1kg mass to accelerate at a rate of 1m/s/s. • 1 N (Newton) = 1 kg * m/s2 • We use a spring scale to measure force.
- 8. Forces in the Same Direction • When forces are applied in the same direction, they are added to determine the size of the net force.
- 9. • When two forces act in opposite directions, you subtract the smaller force from the larger force to determine the net force. • The net force will be in the same direction as the larger force. Forces in Different Directions
- 10. Balanced and Unbalanced Forces • Forces occur in pairs and they can be either balanced or unbalanced
- 11. Balanced forces are forces that are equal in magnitude and in opposite direction so there will be no motion in an object. Unbalanced forces mean that if an object initially is at rest is under an unbalanced force, it moves in the direction of the unbalanced force.
- 12. Balanced Forces:The forces in each direction are“equal”. If more than one force is present, it does not have to cause an acceleration on an object. If another force “balances” the first out, there will be no acceleration at all. Think: If both guys (who weight the same) pull on a rope in opposite directions, with an equal amount of force, how much will they move?
- 13. Balanced Forces • Balanced forces do not cause a change in motion • They are equal in size and opposite in direction • The net force is 0
- 14. Net Force •The sum of all forces acting on an object and direction.
- 15. Example: Gravity pulls down on you… The ground pushes back up… THIS KEEPS YOU WHERE YOU ARE! If these football players push on each other equally as hard, will either one move? Gravity pulls down Ground pushes up
- 16. Forces may cancel each other and produce no movement =No Acceleration! More Balanced Forces… 5 N 5 N
- 17. Forces may cancel each other and produce no movement =No Acceleration! More Balanced Forces… 5 N 5 N
- 18. • Balanced Forces - are forces that are equal in magnitude and in opposite direction so there will be no motion
- 19. TENSION FORCE - acts in the opposite direction of the gravitational force. GRAVITATIONAL FORCE – is the force of attraction between all masses in the universe ; pulls object towards the center of the Earth. The NORMAL FORCE is the force that surfaces exert to prevent solid objects
- 20. The vase stays at rest because it has a normal force of 5 units and gravitational force of 5 units also. Lets find out what will be the net force of the vase? GRESA Method Given: Fn (Normal force) - 5 units Fg (Gravitational force - 5 units Required: F net (Net force) Equation: Fnet = Fn + Fg Solution: Fnet = 5 units + (-5 units) Answer: 0
- 21. 200 N up - 600 N down = 400 N down
- 22. “Unbalanced”Forces If the multiple forces acting at one time are not balanced out (equal), then acceleration can/will occur on the object! Kicking the ball causes it to move quickly in a different direction If one side of the scale has more mass, then gravity will accelerate it down!
- 23. Unbalanced Forces • An unbalanced force always causes a change in motion • The net force is greater than 0 • When unbalanced forces act in opposite directions you can find the net force – Net force • Magnitude –The difference between the two forces • Direction –Direction of the largest force
- 24. Unbalanced Forces 3 N, right – 6 N, left = 3N, left
- 25. Unbalanced Forces 4 N, left – 10 N, right = 6N, right
- 26. Unbalanced Forces 5 N, right + 10 N, right =15N, right
- 27. Unbalanced Forces Cause Acceleration Adding Forces: 5 N Random Object 5 N Notice that all the new forces are pointed in the same direction, and they add together! So, instead of only 5N of force pushing the object; now there are 10 N of force pushing! Multiple forces can combine to move an object that has too much inertia for one force alone.The forces“add together”! All by himself, one person might not be able to push a car. But with extra friends pushing, it becomes much easier! The forces add together. What you just saw was like two people pushing on the same box.
- 28. Unbalanced Forces Cause Acceleration Subtracting Forces: 5 N 5 N Object 5 N Notice that the forces are “unequal” and pointed in the opposite direction. So they are “unbalanced” and work against each other – or one partially cancels the other. The end result is that the forces on the left are slowed down by the single force on the right If forces are not equal and are acting in opposite directions,a negative acceleration can/will occur.The forces will subtract from each other!
- 29. • Unbalanced Forces - if an object is at rest is under an unbalanced force, it moves in the direction of the unbalanced force • Object changes its state of motion (either increase or decrease in acceleration). • Friction force is a force that acts between surfaces that are in contact with one another. In the case of the rolling ball, the frictional force acts between the surface of the ball and the table and slows down the motion of the ball.
- 30. One team pulls 5units to the left and the other team exert forces of 10 units to the right. What will be the net force? To what direction will it be pulled? Given: F1 = -5 units F2 = 10 units Required: F net (Net force) Equation: Fnet = F1 + F2 Solution: Fnet = -5 units + 10 units Answer: 5 units to the right GRESA Method Note: -5 since to the left direction 10 since to the right direction then: apply the basic rules in algebra.
- 31. Review Balanced Forces Balanced Push i.e. Pushing a Car No Acceleration or change in motion Net Force = 0 Balanced Pull i.e. Tug-o-war No Acceleration or change in motion Net Force = 0 10N 10N 10N 10N
- 32. Review Un-Balanced Forces Add Together Un-Balanced Same Direction Faster Acceleration Net Force > 0 Subtract from each other Un-Balanced Opposite Direction Slower Acceleration Net Force > 0 10N 10N 10N 10N 10N
- 33. Combining Forces • Net Force – The overall force acting on an object after all forces are combined. - Forces in the same direction we add them. - Forces in opposite directions you subtract them. 10N 10N = + Net Force = 20N 10N 7N - = Net Force = 3N
- 34. What is the net force? 25 N right – 30 N left = 5 N left What is the net force? Let’s Try!
- 35. What is the net force? 20N right + 20 N right = 40 N right What is the net force? Let’s Try!
- 36. What is the net force? 30 N right + 50 N right – 20 N left = 60 N right What is the net force? Let’s Try!
- 37. What is the net force? 55 N right - 20 N left – 35 N left = 0 N balanced What is the net force? Let’s Try!
- 38. What is the net force? 3 N left - 5 N right = 2 N right What is the net force? Let’s Try!
- 39. BALANCED BALANCED UNBALANCED UNBALANCED
- 42. F= 14 N UNBALANCED F= 10 N UNBALANCED F= 0 N BALANCED
- 43. Learning Task No. 5: Choose the letter of the correct answer. Write your answer on a separate sheet of paper. 1. What forces act on the vase on top of the table? I. Force exerted by the table II. Force of gravity III. Tension force IV. Spring force A. I and II C. I, II and III B. II, III and IV D. I, II, III and IV 2. Which of the following vehicle below has greater inertia? A. a car C. a bicycle B. a truck D. a motorcycle 3. When forces that act on an object are opposite in direction and equal in magnitude, the forces are said to be? A. Friction B. Balanced C. Gravitational D. Unbalanced
- 44. 4. What causes the rolling ball to stop when there is no one to push it continuously? A. Forces acting on the ball are already used up. B. The forces acting on the ball were continuously increasing. C. Unbalanced force causes the rolling ball to change its motion. D. Gravitational force causes the rolling ball to change its motion. 5. What are the forces present on a lantern that is being hang on a tree? A. Normal force and tension force. B. Frictional force and normal force. C. Gravitational force and normal force. D. Gravitational force and tension force. 6. When the net force of an object is equal to zero, then the forces are said to be __________. A. balanced force C. gravitational B. unbalanced force D. Air –resistance force
- 45. Learning Task No. 5: Choose the letter of the correct answer. Write your answer on a separate sheet of paper. 1. What forces act on the vase on top of the table? I. Force exerted by the table II. Force of gravity III. Tension force IV. Spring force A. I and II C. I, II and III B. II, III and IV D. I, II, III and IV 2. Which of the following vehicle below has greater inertia? A. a car C. a bicycle B. a truck D. a motorcycle 3. When forces that act on an object are opposite in direction and equal in magnitude, the forces are said to be? A. Friction B. Balanced C. Gravitational D. Unbalanced
- 46. 4. What causes the rolling ball to stop when there is no one to push it continuously? A. Forces acting on the ball are already used up. B. The forces acting on the ball were continuously increasing. C. Unbalanced force causes the rolling ball to change its motion. D. Gravitational force causes the rolling ball to change its motion. 5. What are the forces present on a lantern that is being hang on a tree? A. Normal force and tension force. B. Frictional force and normal force. C. Gravitational force and normal force. D. Gravitational force and tension force. 6. When the net force of an object is equal to zero, then the forces are said to be __________. A. balanced force C. gravitational B. unbalanced force D. Air –resistance force
- 48. Thank You!
- 49. END OF LESSON 2