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Forces and Newton’s Laws Ch 6, 7.1
Force <ul><li>a push or a pull </li></ul><ul><li>Measured in Newtons (N) </li></ul>
Types of Forces
Gravitational Force <ul><li>Attractive force that exists between all objects </li></ul><ul><li>Weakest of the 4 forces, bu...
Electromagnetic <ul><li>Gives materials their strength, ability to bend, squeeze, stretch, etc. </li></ul>
Strong Nuclear Force <ul><li>Holds the particles in a nucleus together </li></ul><ul><li>strongest of the 4 forces, but ac...
Weak force <ul><li>Involved in the radioactive decay of some nuclei </li></ul><ul><li>form of the electromagnetic force </...
Newton’s Laws of Motion
1 st  Law - Inertia <ul><li>Any object will continue at constant velocity until acted on by some outside force. </li></ul>
2 nd  Law - F=ma <ul><li>The acceleration of an object is directly proportional to the net force on it and inversely propo...
3 rd  Law - Action-Reaction pairs <ul><li>For every action there is an equal and opposite reaction. </li></ul>
Question <ul><li>The horse knows if he pulls with 100N of force and the carriage pulls back with 100 N of force then the c...
Net Force vs Action-Reaction Pairs <ul><li>Action-reaction pairs work on different objects and they are always equal to op...
Mass vs Weight <ul><li>Mass - amount of matter or inertia an object has. </li></ul><ul><li>Weight - gravitational force ex...
Friction <ul><li>Force that opposes motion between 2 surfaces that are in contact. </li></ul>
Types of Friction
Static Friction <ul><li>Force that opposes the start of motion. </li></ul>
Sliding (Kinetic) Friction <ul><li>Force that opposes motion once the object is moving. </li></ul><ul><li>Note: Static fri...
Example Problems <ul><li>A 12 kg box that is pulled across the floor at 2 m/s 2  with a force of 40 Newtons.  Find the coe...
Equilibrant <ul><li>Force equal and opposite to the resultant. </li></ul><ul><li>Ex: Find the equilibrant for 20 N @ 125 d...
Example Problems <ul><li>A 30 kg box is on a 35 degree incline plane.  Find: </li></ul><ul><li>A.  The force that causes t...
<ul><li>A 400 kg sign is hung by cables that are 110 degrees apart.  Find the tension in each cable. </li></ul>
<ul><li>A 50 kg box is pulled across the ground with a force of 300 Newtons @ 35 degrees and  μ  = 0.3.  Find the accelera...
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Forces and newton’s laws

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Transcript of "Forces and newton’s laws"

  1. 1. Forces and Newton’s Laws Ch 6, 7.1
  2. 2. Force <ul><li>a push or a pull </li></ul><ul><li>Measured in Newtons (N) </li></ul>
  3. 3. Types of Forces
  4. 4. Gravitational Force <ul><li>Attractive force that exists between all objects </li></ul><ul><li>Weakest of the 4 forces, but acts over the longest distance </li></ul>
  5. 5. Electromagnetic <ul><li>Gives materials their strength, ability to bend, squeeze, stretch, etc. </li></ul>
  6. 6. Strong Nuclear Force <ul><li>Holds the particles in a nucleus together </li></ul><ul><li>strongest of the 4 forces, but acts over the smallest distance. </li></ul>
  7. 7. Weak force <ul><li>Involved in the radioactive decay of some nuclei </li></ul><ul><li>form of the electromagnetic force </li></ul>
  8. 8. Newton’s Laws of Motion
  9. 9. 1 st Law - Inertia <ul><li>Any object will continue at constant velocity until acted on by some outside force. </li></ul>
  10. 10. 2 nd Law - F=ma <ul><li>The acceleration of an object is directly proportional to the net force on it and inversely proportional to its mass. </li></ul>
  11. 11. 3 rd Law - Action-Reaction pairs <ul><li>For every action there is an equal and opposite reaction. </li></ul>
  12. 12. Question <ul><li>The horse knows if he pulls with 100N of force and the carriage pulls back with 100 N of force then the carriage isn’t going to move. Is his logic right? </li></ul>
  13. 13. Net Force vs Action-Reaction Pairs <ul><li>Action-reaction pairs work on different objects and they are always equal to opposite; EX : I pull on the cart and the cart pulls on me. </li></ul><ul><li>Net force is the sum of all forces and it causes acceleration; the forces work on the same object; EX: I pull on the cart and friction pulls on the cart. </li></ul>
  14. 14. Mass vs Weight <ul><li>Mass - amount of matter or inertia an object has. </li></ul><ul><li>Weight - gravitational force exerted by the earth on an objects mass. </li></ul><ul><li>W=mg </li></ul><ul><li>Normal Force - force that is perpendicular to the contact surface. </li></ul>
  15. 15. Friction <ul><li>Force that opposes motion between 2 surfaces that are in contact. </li></ul>
  16. 16. Types of Friction
  17. 17. Static Friction <ul><li>Force that opposes the start of motion. </li></ul>
  18. 18. Sliding (Kinetic) Friction <ul><li>Force that opposes motion once the object is moving. </li></ul><ul><li>Note: Static friction is greater than sliding friction because of Newton’s First Law </li></ul><ul><li>F f = μ N </li></ul>
  19. 19. Example Problems <ul><li>A 12 kg box that is pulled across the floor at 2 m/s 2 with a force of 40 Newtons. Find the coefficient of friction. </li></ul><ul><li>A 400 kg crate is accelerated upward at 3 m/s 2 by a crane. Find the tension in the cable. </li></ul>
  20. 20. Equilibrant <ul><li>Force equal and opposite to the resultant. </li></ul><ul><li>Ex: Find the equilibrant for 20 N @ 125 degrees. </li></ul><ul><li>Answer: 20 N @ 305 degrees </li></ul>
  21. 21. Example Problems <ul><li>A 30 kg box is on a 35 degree incline plane. Find: </li></ul><ul><li>A. The force that causes the box to move down the incline. </li></ul><ul><li>B. The normal force. </li></ul><ul><li>C. The acceleration if μ = 0.25 </li></ul>
  22. 22. <ul><li>A 400 kg sign is hung by cables that are 110 degrees apart. Find the tension in each cable. </li></ul>
  23. 23. <ul><li>A 50 kg box is pulled across the ground with a force of 300 Newtons @ 35 degrees and μ = 0.3. Find the acceleration. </li></ul>
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