1. FORCES

2. 9/7/2006ISP 209 - 2B2 Which vehicle exerts a greater force ― the tow truck or the car?

3. What is a force? A push or a pull When one object pushes or pulls another object, you say that the first object exerts a force on the second object. Let’s practice. What forces are at play around you?

4. What forces are exerted?

5. Playing catch with a medicine ball

6. 9/7/2006ISP 209 - 2B6 Playing catch with a medicine ball A throws the ball and B catches it.  four forces When A throws the ball he exerts a force on the ball (toward the right) and the ball exerts a force on him so he recoils (toward the left). A B When B catches the ball he exerts a force on the ball (toward the left to stop it) and the ball exerts a force on him so he is knocked back (toward the right).

7. Scalars and Vectors Are both quantities BUT….. Scalars are fully described by magnitude (magnitude= number) Vectors are fully described by both magnitude(number) and direction Let’s take a minute to discuss….

8. QUANTITYSCALAR or VECTOR? 5 m 30 m/sec, East 5 mi., North 20 Degrees Celsius 256 bytes 4000 calories

9. QUANTITYSCALAR or VECTOR? 5 mScalar 30 m/sec, EastVector 5 mi., NorthVector 20 Degrees CelsiusScalar 256 bytesScalar 4000 caloriesScalar

10. What is force categorized as? Force is described by the strength and direction in which it acts. Therefore, Force is a

11. The strength of force is measured in… The SI unit called the Newton (N) One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s. Thus, the following unit equivalency can be stated:

12. Combining Forces Often, more than one force acts on an object at a time. Net force is the combination of all forces acting on the object What does the net force determine? – Motion – direction

13. Net force Practice For each diagram, write the net force and direction. HINT: The net force always acts in the direction of the greater force.

14. Balanced forces Equal forces acting on one object in opposite directions.

15. Balanced Forces Balanced forces result in equilibrium How can I make this box in equilibrium?

16. Unbalanced Forces Unbalanced forces result when the forces exerted on an object are not equal. Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.

17. Free-Body Diagrams Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.

18. Draw a free body diagram A physics book is sitting on a table and is pushed 10 N to the right. The opposing frictional force is 7 N.

19. 9/7/2006ISP 209 - 2B19 Resolution: Consider each part separately, and don’t forget that there are other forces acting. So how can they start moving, or accelerate? A puzzle Horse and Cart The horse pulls the cart with a force A (to the right). According to Newton, the cart pulls the horse with a force –A (to the left).

20. Homework Read Introduction of Forces notes Give 3 examples of force for each of the following: (YOUR OWN EXAMPLES!) – Gravity – Tension – Friction – Drag/Air resistance