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2.1 Force

2.1 Force. What is a force?. Measured quantity Force. SI Unit Newton. Symbol N. A force is a push or a pull. 2.1 Force. Net Force. The combination of all forces acting on an object is called the net force. 2.1 Force.

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2.1 Force

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  1. 2.1Force • What is a force? Measured quantity Force SI Unit Newton Symbol N A force is a push or a pull.

  2. 2.1Force Net Force The combination of all forces acting on an object is called the net force.

  3. 2.1Force An unbalancedforce is needed to change an object’s state of motion. A force is a push or a pull.

  4. 2.1Force Net Force The combination of all forces acting on an object is called the net force. The net force on an object changes its motion (as long as the net force is greater than zero). Measured quantity Force SI Unit Newton Symbol N

  5. 2.1Force Balanced vs. Unbalanced Force Balanced force occurs when the net force = 0 N (the object experiences no change in motion) Unbalanced force occurs when the net force > 0 N (the object experiences a change in motion) • It takes an unbalanced force to change the motion of an object!

  6. 2.1Force Normal Force Net Force When the girl holds the rock with as much force upward as gravity pulls downward, the net force on the rock is zero. • Fnorm = Fgrav Gravity

  7. 2.1Force Net Force The net force depends on the magnitudes and directions of the applied forces. • The blue arrows are called vectors (they indicate size and direction)

  8. 2.1Force Net Force The net force depends on the magnitudes and directions of the applied forces. • The blue arrow in the net force column is a type of vector called the resultant (5 N + 10 N = 15 N)

  9. 2.1Force Net Force The net force depends on the magnitudes and directions of the applied forces.

  10. 2.1Force Net Force The net force depends on the magnitudes and directions of the applied forces. • 10 N – 5 N = net force of 5 N to the right

  11. 2.1Force Net Force The net force depends on the magnitudes and directions of the applied forces.

  12. 2.1Force Net Force The net force depends on the magnitudes and directions of the applied forces. • 5 N – 5 N = net force of 0 N …which is equilibrium!

  13. 2.1Force Force Vectors can be drawn to scale This vector represents a force of 60 N to the right. N • Vectors show magnitude (size) and direction

  14. The sum of two or more vectors Can show the magnitude and direction of the net force. Resultant

  15. Resultant (forces in same direction and in opposite directions) 40 N 20 N Net force = 60 N to the right Resultant? 40 N 20 N Net force = 20 N to the right Resultant?

  16. Resultant (pulling or pushing at an angle)

  17. Resultant (pulling or pushing at an angle)

  18. Identify the resultant and the horizontal and vertical forces

  19. 2.1Force How can you change an object’s state of motion? • Apply a net force greater than zero.

  20. An object in mechanical equilibrium is stable, without changes in motion.

  21. Things that are in balance with one another illustrate equilibrium. Things in mechanical equilibrium are stable, without changes of motion. The rocks are in mechanical equilibrium. • http://library.thinkquest.org/27638/leaning.html

  22. http://sciencefair.math.iit.edu/projects/pisa/ • An object will fall if its center of mass is no longer situated within its base

  23. Different Types of Forces Gravity (also called weight) Friction Applied Force Air Resistance Tension Spring Force Normal Force (also called support force) http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/newtlaws/u2l2b.html#spring

  24. Gravity Tension Force Spring Force Applied Force Friction Air Resistance Normal force Force of attraction due to mass of an object Pulled force applied to a rope, wire or cable Elastic, compressed or stretched force Any push or pull on an object Resistance of two objects in contact moving past each other Resistance of an object moving through the atmosphere Force that pushes back on one object resting on another 2.3 Definition of Forces

  25. For an object at rest on a horizontal surface, the support force (normal force) must equal the object’s weight (gravity). 2.3Support Force

  26. Tension, Weight and Spring 2.1Force The upward tension in the string has the same magnitude as the weight of the bag, so the net force on the bag is zero. The bag of sugar is attracted to Earth with a gravitational force of 2 pounds or 9 newtons. Spring force (in scale) Tension (in string) • 1 lb = 4.45 N Weight (of bag) • 9 N of weight = 9 N of tension and spring force

  27. 2.3Support Force Support Force (also called normal force) The table pushes up on the book with as much force as the downward weight of the book. Fnorm = Fgrav Net force Weight (also called gravity)

  28. 2.3Support Force Physics The book lying on the table compresses atoms in the table and they squeeze upward on the book. The compressed atoms produce the support force.

  29. 2.3Support Force The upward support force is as much as the downward pull of gravity.

  30. 2.3Support Force The upward support force is as much as the downward pull of gravity.

  31. think! What is the net force on a bathroom scale when a 110-pound person stands on it? 2.3Support Force

  32. think! What is the net force on a bathroom scale when a 110-pound person stands on it? Answer: Zero–the scale is at rest. The scale reads the support force, not the net force. 2.3Support Force

  33. think! Suppose you stand on two bathroom scales with your weight evenly distributed between the two scales. What is the reading on each of the scales? What happens when you stand with more of your weight on one foot than the other? 2.3Support Force

  34. think! Suppose you stand on two bathroom scales with your weight evenly distributed between the two scales. What is the reading on each of the scales? What happens when you stand with more of your weight on one foot than the other? Answer: In the first case, the reading on each scale is half your weight. In the second case, if you lean more on one scale than the other, more than half your weight will be read on that scale but less than half on the other. The total support force adds up to your weight. 2.3Support Force

  35. 2.3Support Force For an object at rest on a horizontal surface, what is the support force (or normal force) equal to? • The object’s weight (or gravity)!

  36. Tension and Weight 2.1Force A stretched spring is under a “stretching force” called tension. Pounds and newtons are units of weight, which are also units of force. Weight is a force.

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