CHAPTER 3 _ FORCE.pdf
- 1. CHAPTER 3 FORCE M D M . C H A N G S H E U E N E E L E C T U R E R M A T H E M A T I C S , S C I E N C E & C O M P U T E R D E P A R T M E N T
- 2. OVERVIEW
- 3. WHAT IS FORCE ? Forces - Force is a push or pull upon an object resulting from the object’s interaction with another object. Forces are VECTOR QUANTITY, describe using magnitude (size) and direction SI Unit – Newton (N) @ kgms-2 PUSH PULL
- 5. THE EFFECTS OF A FORCE
- 6. THE EFFECTS OF A FORCE
- 7. THE EFFECTS OF A FORCE
- 8. WEIGHT MASS Definition: The force of gravity on the object Definition: The amount of material in an object SI unit: Newton (N) SI unit: kilogram (kg) Weight depend on the size of the object. The bigger the object, the greater the gravitational pull. Mass does not change with a body's position, movement or alteration of its shape, unless material is added or removed. WEIGHT & MASS
- 10. RELATIONSHIP BETWEEN FORCE, MASS AND ACCELERATION (F=MA)
- 11. EXAMPLE 1
- 12. EXERCISE 1
- 13. 4. A box with a mass of 70 kg is placed on a horizontal floor with a smooth surface. The velocity of the box changes from stationary to 50 m/s in 10 seconds when it is acted on by a force. Find the magnitude of the force. 5. What force will produce an acceleration of 7 m/s-2 in a body of 10 kg? 6. Calculate the mass of a body when a force of 225 N produces an acceleration of 2.5 m/s2. 7. What is the acceleration produced by a force of 10 N acting on a body of mass 200g?
- 14. RELATIONSHIP BETWEEN FORCE, MASS AND ACCELERATION DUE TO GRAVITY (F=MG) It’s only applicable for cases where the object moved in the vertical direction
- 15. EXERCISE 2
- 16. FORCE ACTING AGAINST INCLINED PLANED (F=MG SIN …) θ
- 18. 3. The figure below shows an object with a mass of 10 kg moves down a smooth plane inclined at an angle of 30°. Calculate the force of the object. 30° EXERCISE 3
- 20. FORCES UNBALANCED FORCES BALANCED FORCES AT EQUILIBRIUM Fnet = 0 a = 0 RESOLUTION OF FORCES RESULTANT FORCES
- 21. BALANCED FORCES 1. When all the forces that act upon an object are balanced, then the object is said to be in a state of equilibrium. 2. The forces are considered to be balanced if the rightward forces are balanced by the leftward forces and the upward forces are balanced by the downward forces
- 22. BALANCED FORCES
- 23. Resultant Force = 0 N BALANCED FORCES FORCE AT EQUILIBRIUM
- 24. Fnet = 0, a = 0 Therefore, a stationary object will remain stationary and a moving object will continue moving with the same velocity in a straight line. BALANCED FORCES FORCE AT EQUILIBRIUM
- 25. Which diagram represents a box in equilibrium?
- 26. Calculate the net force acting on the block. EXAMPLE 2
- 27. Calculate the net force acting on each situation. EXERCISE 4
- 28. Calculate the values of F2 so that the objects are in equilibrium. F1 = 100 N F2 = ? N F3 = 150 N F4 = 100 N F5 = 200 N F1 = 10 N F2 = ? N F3 = 4 N θ = 60˚ 60° i) ii) F3 F1 F2 F1 F2 F3 F5 F4 EXERCISE 5
- 29. UNBALANCED FORCES ACTING ON AN OBJECT When the forces acting on an object are not balanced, there will be a net force acting on it. The net force is known as RESULTANT FORCE.
- 30. WHAT IS RESULTANT FORCES Let say u have been given 2 FORCES in the same direction. What is the RESULTANT force…?? Let say u have been given 2 FORCES not in the same direction. _
- 31. FORMULA
- 32. Diagram shows forces acting on an object. Calculate the resulting force acting on the object. EXAMPLE 3
- 33. Diagram shows forces acting on an object. Calculate the resulting force acting on the object. 20N 12N 15N 60o 10N F θ Fx = F cos θ Fy = F sin θ 10 0° 10 cos 0°= 10 N 10 sin 0°= 0 N 15 60° 15 cos 60°= 7.5 N 15 sin 60°= 12.99 N 20 180° 20 cos 180°= -20 N 20 sin 180°= 0 N 12 180° 12 cos 180°= -12 N 12 sin 180°= 0 N ∑Fx = -14.5 N ∑Fy = 12.99 N EXAMPLE 3
- 34. Diagram shows forces acting on an object. Calculate the resulting force acting on the object. 20N 12N 15N 60o 10N F θ Fx = F cos θ Fy = F sin θ 10 0° 10 cos 0°= 10 N 10 sin 0°= 0 N 15 60° 15 cos 60°= 7.5 N 15 sin 60°= 12.99 N 20 180° 20 cos 180°= -20 N 20 sin 180°= 0 N 12 180° 12 cos 180°= -12 N 12 sin 180°= 0 N ∑Fx = -14.5 N ∑Fy = 12.99 N EXAMPLE 3
- 35. Diagram shows forces acting on an object. Calculate the resulting force acting on the object. 20N 12N 15N 60o 10N Calculate the degree of acting force Draw the resulting force diagram EXAMPLE 3
- 36. Calculate the horizontal and vertical components for the forces in figures below: i) 500 N 30° ii) 3000 N 45° EXERCISE 6
- 37. 60° 60° 10° 10° 30° 30° 30° 60° Calculate the resultant force for each of the figures below: EXERCISE 7
- 38. 140° 80° 60°
- 40. WHAT IS RESOLUTION FORCES Resolution of Forces - Breaking down a single vector into 2 or more components. FORCE
- 41. EXAMPLE Resolve the force given below using calculation/analysis method.
- 42. SOLUTION cos x R F F 80 cos 60 80 0.5 4 0 N sin y R F F 80 sin 60 80 0.8660 6 9 .2 8 N