1. VIDEO OF MOTION What cause motion….? A force also can cause: a. a moving object to change its speed c. a moving object to change its direction of motion d. an object to change in size and shape FORCE

2. THE EFFECTS OF A FORCE

3. FORCE 1.A force is a pulling or a pushing action on an object. 2.We make use of forces in our daily life all the time. 3.Forces have magnitude and direction. 4.The unit of force is newton (N) or (kg m s -2 ). 5.A force is not visible but the effects of forces which can be observed.

4. Balanced Force: 1.An object may have several forces acting on it. If the forces are in balance, they cancel each other out. Then, the object behaves as if no force is applied to it (net force or resultant force is 0). The effects of balanced forces on object:

5. 2. With balanced forces on it, an object is either at rest, or moving at a constant velocity. ( net force or resultant force is 0 ).

7. EXAMPLES:Balanced Force 1. Balance forces on a stationary cup AnotherAnother ex.

8. 2. Balance forces on the aircraft result in it moving at constant velocity Another Ex.

9. Unbalanced Force: 1.An object will accelerate when forces acting on it are not balanced. how to know balanced force----  it has net force (resultant force). The effects of unbalanced forces on object:

11. EXAMPLES:Unbalanced Force Example Another Example

12. Relation Between Force, Mass, and Acceleration:

13. A QuestionQuestion

15. SOLVING PROBLEMS 1. When a force acts on a mass of 3 kg, the resultant acceleration is 2 m s -2. Calculate the force……… 3 kg F (N) a = 2 m s -2 F = m am = 3 kg a = 2 m s -2 F = 3 kg 2 m s -2 F = 6 kg m s -2 = 6 N Solution:

16. 2. Azhari applies a force of 50 N to move a 12 kg box at a constant velocity. What is the frictional force acting on the box? Constant velocity ------  acceleration, a=0 Net force in the direction of velocity, F = F 1 - f = 50 N - f from F = ma 50 N – f = 12 kg 0 m s -2 f = 50 N – 0 = 50 N 12 kg F 1 =50 N f Solution:

17. 3. What force is required to move a 2 kg object with an acceleration of 3 m s -2, if: a. the object is on a smooth surface? (f=0) b. the object is on a surface where the average force of friction acting on the object is 2 N? Solution: a.From F = ma F 1 - f = m a F 1 - 0 = 2 kg 3 m s -2 F 1 = 6 N ( a force of 6 N is required to accelerate the object at 3 m s -2 ) b. Net Force (F) = F 1 – f = F 1 – 2 N From F = ma F 1 – 2 N = 2 kg 3 m s -2 F 1 = 6 N + 2 N = 8 N ( a force of 6 N is required to accelerate the object at 3 m s-2 )

18. summary