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# Ch. 2 sec.1-force of nature

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I hope to study and complete all your notes from this presentation to remember all what did we say in the class. Good Luck.

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### Ch. 2 sec.1-force of nature

1. 1. Forces of Nature Gravitational Magnetic
2. 2. The Nature of Force <ul><li>What is a Force? </li></ul><ul><li>A force is a push or a pull. </li></ul><ul><li>Like velocity and acceleration, a force is described by its strength and the direction in which it acts. </li></ul><ul><li>The strength of a force is measured by Newton (N). </li></ul>
3. 3. Net force (Combining force); It is the total amount of Force, ( minus the forces that cancel each other out ). Force of gravity Force of muscles Net force
4. 4. Balanced Forces Unbalanced Forces When the net force is Zero. -> NO movement When the net force is NOT Zero. -> movement
5. 5. 2 Kg ? <ul><li>Static Equilibrium Balanced forces </li></ul><ul><li>When all forces are balanced. </li></ul><ul><li>The net force is Zero. </li></ul><ul><li>There is NO movement. </li></ul>3 Kg
6. 6. 50 N 100 N 100 N 50 N 50 N 50 N
7. 7. Balanced or unbalanced? Action Reaction Gravity Inertia Friction
8. 8. Gravity balanced UN Time (mSec) Speed (m/s) BALL Ground
9. 9. Inertia balanced UN Time (mSec) Speed (m/s) BALL PUTTER
10. 10. Friction balanced UN Time (Sec) Speed (m/s) SKATE
11. 11. <ul><li>Friction results from relative motion between objects. </li></ul><ul><li>Frictional forces are forces that resist or oppose motion. </li></ul>2.2 Friction
12. 12. <ul><li>Static friction </li></ul><ul><li>{A friction that acts on objects that are not moving}. </li></ul><ul><li>Sliding friction </li></ul><ul><li>{ A friction that occurs when two solid surfaces slide above each other}. </li></ul><ul><li>Rolling friction </li></ul><ul><li>{A friction that occurs when an object rolls across a surface. </li></ul>2.2 Types of Friction
13. 13. 2.2 Types of Friction <ul><li>Air friction </li></ul><ul><li>{ A friction that occurs when a solid object moves through the air}. </li></ul><ul><li>Fluid friction </li></ul><ul><li>{ A friction that occurs when a solid object moves through a fluid}. </li></ul>
14. 14. Gravity The Apple & the Moon <ul><li>Isaac Newton realized that the motion of a falling apple and the motion of the Moon were both actually the same motion , caused by the same force - the gravitational force . </li></ul><ul><li>Gravity is a force that pulls objects toward each other. </li></ul>
15. 15. Universal Gravitation <ul><li>Newton’s idea was that gravity was a universal force acting between any two objects . </li></ul><ul><li>Factors Affecting Gravity; </li></ul><ul><li>Mass : is a measure of </li></ul><ul><li>the amount of matter in an </li></ul><ul><li>object. </li></ul><ul><li>Distance : it is </li></ul><ul><li>between two objects. </li></ul><ul><li>The farther apart two objects are, </li></ul><ul><li>the lesser gravitational forces </li></ul><ul><li>Between them. </li></ul>
16. 16. At the Earth’s Surface <ul><li>Newton knew that the gravitational force on the apple equals the apple’s weight , mg , where g = 9.8 m/ s 2 . </li></ul><ul><li>Gravitational force </li></ul><ul><li>INCREASES with Mass </li></ul><ul><li>DECREASES with Distance </li></ul>W = mg
17. 17. Gravity and Motion Free Fall Free fall- when gravity is the only force acting on an object (free fall acceleration is directed toward center of earth) The acceleration of gravity ( g ) for objects in free fall at the earth's surface is 9.8 m/s 2 . Galileo found that all things fall at the same rate in the absence of air resistance, regardless of their mass
18. 18. Air Resistance <ul><li>In air… </li></ul><ul><ul><li>A stone falls faster than a feather </li></ul></ul><ul><ul><ul><li>Air resistance affects stone less </li></ul></ul></ul><ul><li>In a vacuum </li></ul><ul><ul><li>A stone and a feather will fall at the same speed. </li></ul></ul><ul><ul><li>Terminal Velocity : it is reached when the force of air resistance equals the weight of the object </li></ul></ul>
19. 19. Projectile Motion When an object is thrown into the air, two forces and two motions affect the movement of the object. The object may be thrown horizontally with a certain force, but the vertical force of gravity combines to affect the motion. Slow projectile - shoot a monkey Fast projectile - shoot a monkey
20. 20. Projectile Motion seconds 0 2 1 3 Velocity (m/s) forward downward 0 50 9.8 19.6 29.4 39.2
21. 21. Projectile Motion seconds 0 2 1 3 Velocity (m/s) forward downward 0 50 9.8 19.6 29.4 39.2 49 48 47 46