1. Section 3Motion In some cases, an applied force is balanced by an opposite force, and there is no change in motion. In other cases, an applied force is not balanced by an opposite force, and the result is acceleration in the direction of the applied force. Look at the following illustrations, and identify the forces and motion in each one. Bellringer

2. Section 3Motion 1. In one drawing, no motion is likely to occur. Which drawing is it? 2. In which diagram are the forces clearly balanced? How does this relate to your answer to item 1? If more force is exerted by the person, does the opposite force increase to match the new force, stay the same, or decrease? 3. Suppose there is enough friction in the wheels of the wagon in diagram c to balance the force with which the wagon is pulled. How will this affect the motion of the wagon? Bellringer, continued

3. Section 3Motion SPS8 Students will determine relationships among force, mass, and motion.

4. Section 3Motion EQ: How are force and motion related?

5. Section 3Motion Fundamental Forces What do scientists identify as the fundamental forces of nature?

6. Section 3Motion 11-3-1 Fundamental Forces These forces are the force of gravity, the electromagnetic force, the strong nuclear force, and the weak nuclear force.

7. Section 3Motion 11-3-2 Fundamental Forces The strong and weak nuclear forces act only over a short distance.

8. Section 3Motion 11-3-3 Fundamental Forces, continued The fundamental forces vary widely in strength and the distance over which they act.

9. Section 3Motion 11-3-4 Fundamental Forces, continued Forces can act through contact or at a distance.

10. Section 3Motion 11-3-5 Fundamental Forces, continued Pushes and pulls are examples of contact forces.

11. Section 3Motion 11-3-5 Fundamental Forces, continued Field forces (like the force of gravity) do not require that the objects touch each other.

12. Section 3Motion 11-3-6 Fundamental Forces, continued Both contact and field forces can cause an object to move or to stop moving.

13. Section 3Motion Balanced and Unbalanced Forces What happens when there is a net force acting on an object?

14. Section 3Motion 11-3-7 Balanced and Unbalanced Forces Whenever there is a net force acting on an object, the object accelerates in the direction of the net force.

15. Section 3Motion 11-3-8 Balanced and Unbalanced Forces net force: the combination of all forces acting on an object

16. Section 3Motion 11-3-9 Balanced and Unbalanced Forces, continued Balanced forces do not change motion.

17. Section 3Motion 11-3-10 Balanced and Unbalanced Forces, continued Forces are balanced when the net force is zero.

18. Section 3Motion 11-3-11 Balanced and Unbalanced Forces, continued Example: For a light hanging from the ceiling (at rest), the upward force due to tension in the cord balances the downward force of gravity.

19. Section 3Motion 11-3-12 Balanced and Unbalanced Forces, continued Unbalanced forces do not cancel completely.

20. Section 3Motion 11-3-13 Balanced and Unbalanced Forces, continued Forces are unbalanced when the net force is greater than zero.

21. Section 3Motion 11-3-14 Balanced and Unbalanced Forces, continued The object will accelerate in the direction of the net force.

22. Section 3Motion 11-3-15 Balanced and Unbalanced Forces, continued Example: If you push a box to the east and your friend pushes the box to the north, the box will accelerate in a northeasterly direction.

23. Section 3Motion The Force of Friction What force always opposes motion?

24. Section 3Motion 11-3-16 The Force of Friction friction: a force that opposes motion between two surfaces that are in contact

25. Section 3Motion 11-3-17 The Force of Friction, continued static friction: the force that resists the initiation of sliding motion between two surfaces that are in contact and at rest

26. Section 3Motion 11-3-18 The Force of Friction, continued kinetic friction: the force that opposes the movement of two surfaces that are in contact and are moving over each others

27. Section 3Motion 11-3-19 The Force of Friction, continued Kinetic friction has 3 components: sliding, rolling and fluid Static friction is greater than kinetic friction.

28. Section 3Motion 11-3-20 The Force of Friction, continued sliding friction: when objects slide past each other

29. Section 3Motion 11-3-21 The Force of Friction, continued rolling friction: when a rounded object rolls over a flat surface

30. Section 3Motion 11-3-22 The Force of Friction, continued in general rolling friction < sliding friction

31. Section 3Motion Fluid friction: the use of lubricants and oils to reduce sliding friction. Also the friction of objects moving through water and air.

32. Section 3Motion Friction and Motion Why is friction sometimes necessary?

33. Section 3Motion 11-3-23 Friction and Motion Friction is necessary for many everyday tasks to work correctly.

34. Section 3Motion 11-3-24 Friction and Motion, continued Using low-friction materials, such as nonstick coatings on cooking pans lowers friction.

35. Section 3Motion 11-3-25 Friction and Motion, continued Using lubricants, such as motor oil, wax, and grease lowers friction.

36. Section 3Motion 11-3-25 Friction and Motion, continued Scattering sand on icy roads to keep cars from skidding increases friction.

37. Section 3Motion 11-3-26 Friction and Motion, continued Wearing textured batting gloves when playing baseball make it easier to grip the bat and increases friction.

38. Section 3Motion Friction and Motion, continued Cars could not move without friction. –Without friction between the tires and the road, the tires would not be able to push against the road and the car would not move forward. –The force pushing the car forward must be greater than the force of friction that opposes the car’s motion. –Because of friction, a constant force must be applied to a car just to keep it moving at the same speed.

39. Section 3Motion Friction and Motion, continued