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Net Force

Net Force. Physics 11 Adv. Comprehension Check. An object has a weight of 12.2N; what is its mass? If you were to take the weight of a 1.0kg object on the moon, what would it be? A 5.00kg wooden crate is slid across a wooden floor; what frictional force is experienced by the crate?

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Net Force

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  1. Net Force Physics 11 Adv

  2. Comprehension Check • An object has a weight of 12.2N; what is its mass? • If you were to take the weight of a 1.0kg object on the moon, what would it be? • A 5.00kg wooden crate is slid across a wooden floor; what frictional force is experienced by the crate? • If a 150N force is applied to a 25kg object, what would its acceleration be?

  3. Comprehension Check • 1.24kg • 1.64N • 9.8N • 6.0m/s2

  4. Putting it All Together • Now that we have considered Newton’s Second Law, you can use that to analyze kinematics problems with less information than we have used previously • We can either use dynamics information to then apply to a kinematic situation or vice versa

  5. A free body diagram will be used in most dynamics problems in order to simplify the situation In a FBD, the object is reduced to a point and forces are drawn starting from the point Free Body Diagrams FN Fa Ff Fg

  6. The Net Force • In most situations, there is more than one force acting on an object at any given time • When we draw the FBD we should label all forces that are acting on an object and also determine which would cancel each other out • Ones that do not completely cancel out will be used to determine the net force

  7. The Net Force • The net force is a vector sum which means that both the magnitude and direction of the forces must be considered • In most situations we consider if Physics 11, the forces we consider will be parallel or anti-parallel

  8. An Example • A 25kg crate is slid from rest across a floor with an applied force 72N applied force. If the coefficient of kinetic friction is .27, determine: • The acceleration of the crate? • The time it would take to slide the crate 5.0m across the floor.

  9. FBD FN=250N Fa=72N Ff=? Fg=-250N

  10. Use the frictional force equation to determine the magnitude of the frictional force

  11. The net force is the sum of the forces (acting parallel or anti-parallel)

  12. Use Newton’s Second Law to solve for the acceleration

  13. Use kinematics to solve for the time taken to cross the floor

  14. Pushing or Pulling a Sled – Which is Better?

  15. Pushing a Sled • A child of 35kg is sitting on a sled that has a coefficient of kinetic friction of 0.10 with the snow. If the parent who is pushing the sled pushes down with an angle of 25°, with what force do they need to push to keep the child and sled sliding with a constant velocity?

  16. FBD FN Fa Ff Fg

  17. Break Applied Force into Components Fax Fay Fa

  18. Consider x and y independently

  19. Pulling a Sled • A child of 35kg is sitting on a sled that has a coefficient of kinetic friction of 0.10 with the snow. If the parent who is pulling the sled pulls up with an angle of 25°, with what force do they need to pull to keep the child and sled sliding with a constant velocity?

  20. FBD FN Fa Ff Fg

  21. Break Applied Force into Components Fa Fay Fax

  22. Consider x and y independently

  23. Practice Problems • Page 168 • Questions 4-8 • Page 170 • 9 - 13 • Physics 20 • Page 108 • 1-10 and 17

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