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Mock teaching quest
- 1. DYNAMIC : NEWTON’SLAW OF MOTION • Force ( Applied force, normal force, gravitational force, frictional force) • Newton’s First Laws of Motion • Mass, weight • Newton’s Second Laws of Motion • Newton’s Third Laws of Motion. • Free Body Diagram. • Friction, Coefficient of friction, • Horizontal and Inclines plane. • Solving problem with Newton’s Law: Free Body Diagram. 1
- 2. 2 At the endof this section, students should be able to: LESSON OUTCOMES: 1) Define type of Force (Applied force, normal force, gravitational force, frictional force) • uses the equation F = ma to solve simple problems • states that the unit of force is the newton (N) 2) Newton’s First Laws of Motion • states Newton’s first law 3) Newton’s Second Laws of Motion. • states Newton’s second law 4) Newton’s Third Laws of Motion. • Free Body Diagram. • Friction, Coefficient of friction, • Horizontal and Inclines plane. • Solving problem with Newton’s Law: Free Body Diagram.
- 3. What is aFORCE ? • An interaction between TWO objects or • The cause of motion (what causes objects to move) Two method in producing forces : 3 i) Push ii) Pull .
- 4. An object atrest needs a force to get it moving; a moving object needs a force to change its velocity. The magnitude of a force can be measured using a spring scale. FORCE SI Unit : Newton (N) @ kgm/s2. Quantity : Vector 4
- 5. • An appliedforce is a force that is applied to an object by a person or another object. • If a person is pushing a box across the room, then there is an applied force acting upon the object. • The applied force is the force exerted on the box by the person. 5 APPLIED FORCE, F
- 6. Forces may causethe object - balanced or unbalanced • Balanced forces – all forces acting on an object are equal – There is NO MOTION • A net force is ZERO ( ∑F = 0 ) • Unbalanced forces – one or more forces acting on an object are stronger than others – There is MOTION • A net force have value ( ∑F ≠ 0 ) 6 BALANCED AND UNBALANCED FORCE
- 7. •Arrows are usedto represent forces. The length of the arrow is proportional to the magnitude of the force. • Net force : The vector sum of all forces acting on that object. Individual Forces Net Force 6 N10 N4 N FORCE 7
- 8. • Gravitational forceor weight, W is the force exerted on that object by gravity. Mass is measured in kilogram (kg) • Mass is not weight • Direction: directly downward from the object. Fg or W = mg W Gravitational Force, Fg 8
- 9. Normal Force, FN 9 •A reaction force exerted by surface • Cannot exist on its own • Direction: Always perpendicular to the surface W FN object floor Also called reaction force.
- 10. Frictional Force, Ff 10 •Force that always oppose the motion of the object • Exist at rough surface F Ff Coefficient of friction Normal Force Nf μFF
- 11. Tensional Force, FT 11 •Exist at rope, cable • Direction: always away from body • Tension at smooth pulley (frictionless pulley) always similar, hence FT1 = FT2 FT1 FT2
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- 15. NEWTON’S FIRST LAW Anobject at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force. • When no force acts on an object, F = 0, a = 0 • Also called law of inertia • Inertia is the tendency for object to resist change in its velocity. 15
- 16. Mass & Inertia •Mass is the amount of matter in an object. • The more MASS an object has, the more INERTIA the object has. • Bigger objects are harder to start & stop 16 Which vehicle has more inertia?
- 17. When the netforce acting on an object is not zero, the object will accelerate at the direction of the exerted force. The acceleration is directly proportional to the net force and inversely proportional to the mass. NEWTON’S SECOND LAW 17 m m F aaF ,
- 18. Exercise 1 :Lets try this!! Determine the accelerations which result when a 12-N net force is applied to a 3 kg object and then to a 6 kg object. Solution: 18
- 19. Newton’s third law: •Whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first. For every action, there is an equal and opposite reaction. NEWTON’S THIRD LAW 19
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- 21. Free Body Diagram(FBD) 21 1. For one object, draw a free-body diagram, showing all the forces acting on the object. 2. Label each force. If there are multiple objects, draw a separate diagram for each one. 3. Resolve vectors into components. 4. Apply Newton’s law to each component. 5. Solve. R W
- 22. 22 Exercise : DrawFree Body Diagram for figure below a) b) c) Inclined plane (smooth surface) d ) Inclined plane (rough surface) θ θ
- 23. 23 Exercise : DrawFree Body Diagram for figure below e) f) g) smooth surface rough surface
- 24. Exercise 1 :Lets try this!! Suppose the coefficient of kinetic friction is 0.05 and the total mass is 40kg. What is the kinetic frictional force? 24
- 25. Solution : 25 ( Ans: 19.6 N)
- 26. Exercise 2 :Lets try this!! A 10.0-kg box is pulled along a horizontal surface by a force of 40.0 N applied at a 30.0° angle above horizontal. The coefficient of kinetic friction is 0.30. Calculate the acceleration. 30° 26
- 27. Solution : 27 ( Ans: 1.12 m/s2 )
- 28. Exercise 3 :Lets try this!! A box of mass 10kg is placed on a smooth incline that makes an angle 30° with the horizontal. (a) Draw the FBD (b) Determine the normal force on the box. (c) Determine the box’s acceleration. 28
- 29. Solution: 29 ( Ans :84.87 N, 4.9 m/s2 )
- 30. 3 kg 2 kgm1 m2 Exercise3 : Lets try this!! Find the acceleration of the pulley system as in the figure. Solution: 30 ( Ans 1.96 m/s2 )
Editor's Notes
- #12 Smooth pulley = frictionless. Mean their acceleration is must be of equal magnitude. If object 1 accelerate upward, object 2 is accelerate downward.
- #21 A key to the correct application of the third law is that the forces are exerted on different objects. Make sure you don’t use them as if they were acting on the same object.