3. The Forces Are With Us

4. More than one force can act on an object at once. The net force acting on an object is the total of all the individual forces acting on the object. Net force changes an object’s state of motion. A force is a push or a pull that one object exerts on another object.. 1, 2, 3

6. The Fundamental Forces in Nature These forces act at a distance 1.Gravitational Force 2.Electromagnetic Force 3.Strong Force (binds protons and neutrons in the nucleus of the atom 4.Weak Force - force of nature that underlies some forms of radioactivity and certain interactions between subatomic particles. 4

8. Contact Forces Contact Forces are forces in which interacting objects are in contact with each other. Examples of contact forces are: 1.Friction Force – force that acts between materials that touch as they move past each other. 2.Air resistance Force – Acts upon objects as they travel through the air. 3.Applied Force – Force that is applied to an object by another object or by a person. 5, 6

9. Friction Force F (frict) The friction force is the force exerted by a surface as an object moves across it, or makes an effort to move across it. Most of the time, the friction force opposes the motion of an object. 7

10. Tension Force F (tens) The tension force is the force which is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire. 8

11. Applied Force F (app) An applied force is a force which is applied to an object by a person or another object. 9

12. Air Resistance Force F (air) The air resistance force is a special type of frictional force Which acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the Motion of an object. It is most noticeable for objects which Travel at high speeds or for objects with large surface areas. 10

13. Normal Force F (norm) The normal force is the support force exerted upon an Object which is in contact with another stable object. More on the normal force will come later. 11

14. Gravity Force F (grav) The force of gravity acts over a distance. The force of gravity if the force with which the earth, moon or other massively large objects attracts another object toward itself. By definition, this is the weight of the object. The force of gravity on earth is always equal to the weight of the object as found in the equation 12, 13

15. Anyone can learn about the forces!

16. The force of gravity pulling you and the skateboard downward towardgravity the earth (gravitational force). The force of your pushing the skateboard with your foot (applied force). The force of the air pushing against you. (air resistance force). The force of a wall pushing back on the skateboard when the skateboard hits the wall (applied force). The force exerted by the surfaces of the wheels and the floor as they move across each other. (friction force).

17. Motion does not occur with balanced forces because they cancel each other out. 14,15 When forces are balanced, net force is always 0.

18. Balanced Forces When the forces acting on an object are in opposite directions and equal in size, the forces are said to be balanced. 16

19. The table pushes upward on the book Gravity pulls the book downward. The forces acting on the book are balanced. They are equal in size but are acting in opposite directions. The book is not moving. Net force = 0.

20. Unbalanced forces (also called Net Forces) are unequal forces acting on an object. During the tug-of-war competition, one team is finally able to overcome and apply more pulling force to the rope. The rope starts to move in that teams favor. Motion can only occur when an unbalanced force (net force) acts on an object. 17,18

21. The downward force of gravity and the upward force of the table supporting the book are of equal magnitude, act in opposite directions and thus balance each other. However, the force of friction acts leftwards, and there is no rightward force to balance it. In this case, an unbalanced forceunbalanced force acts upon the book to change its state of motion and the bookstate of motion slows.

22. Mass is not volume. Volume is a measure of the space an object occupies. The pillow takes up more space, therefore it has more volume than the battery. However the battery has more mass. The battery is harder to move and has more inertia. 19

23. Mass Is Not Weight. Mass is the amount of matter in an object. Weight is a measure of the gravitational force acting on an object.. Weight depends on an object’s location. Mass does not. 20,21

24. Formula for calculating weight: Weight = mass x gravity Weight is a force. The unit for force is the Newton. 1 kilogram of mass is equal to 9.8 Newtons of force. 1 kg = 9.8 Newtons 22,23,24

25. Weight can vary with location because gravity can be different. Mass stays the same regardless of location. The Earth has more mass than the Moon, so the gravitational force is greater on the Earth than it is on the Moon.

26. Aristotle gave three reasons for motion: 1.Natural motion, such as falling, came from the tendencyof objects to go to their “natural” place, on the ground, and come to rest. 2.Natural motion was the type of motion exhibited by animals, which moved because they chose to. 3.Violent motion occurred when an object was acted on by some other object that made it move

27. Nicolaus Copernicus (1473-1543) Formulated a theory for the Moving Earth. Copernicus reasoned that the the best way to interpret astronomical observations was to assume that the Earth and other planets move around the Sun. Copernicus worked on his ideas in secret to avoid persecution. 25

28. Work primarily dealt with describing motion and kinematics. Was the first to believe that a force was needed to keep an object moving only when friction was present. He was aware of the concept of inertia. He rejected Aristotle's ideas of violent and natural motions after studying falling or rolling objects and projectiles. Galileo Galilei (1564 - 1642) 26

29. A Master and an Apprentice Sir Isaac Newton (1642 - 727) Yoda ??

30. Newton’s First Law is also called The Law of Inertia. Inertia (mass) is the tendency of an object to resist any change in its motion. Mass is a measure of the inertia of an object. 27, 28, 29

31. Every object continues in a state of rest, or in a state of motion in a straight line at constant line at constant speed, unless it is compelled to change by the state of forces acting on it. The Law of Inertia deals with forces when they are balanced. According to Newton, an object placed in motion in a straight line will continue in motion forever until some outside force acts on the object to change its motion. Law of Inertia 30, 31, 32

32. A force is not needed to keep an object in motion. The more mass an object has, the greater the inertia and the more force it takes to change its state of motion. 33, 34

33. The law of inertia explains what happens in a car crash.

34. No seat belt!!!

35. If the car were to abruptly stop and the seat belts were not being worn, then the passengers in motion would continue in motion. Assuming a negligible amount of friction between the passengers and the seats, the passengers would likely be propelled from the car and be hurled into the air. Once they leave the car, the passengers becomes projectiles and continue in projectile-like motion

37. A force is not required to keep an object in motion; in actuality, it is a force which brings the object to rest. In the absence of a changing force, objects will continue in motion with the same speed and in the same direction – forever!

38. May The Force Be with You! The End!