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BELLWORK 12/10/18

Learn about the causes of motion and the role of force in changing an object's speed or direction. Explore the concept of inertia and practice drawing free-body diagrams to analyze forces acting on objects.

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BELLWORK 12/10/18

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  1. BELLWORK 12/10/18 • What causes motion? (What do you think causes objects to move?)

  2. 4.1 The First Law: Force and Inertia Objects in motion remain in motion at a constant speed in the same direction and objects at rest remain at rest unless acted upon by an unbalanced force.

  3. 4.1 Force Forceis an action that can change motion. A force is what we call a push or a pull, or any action that has the ability to change an object’s motion. Forces can be used to increase the speed of an object, decrease the speed of an object, or change the direction in which an object is moving.

  4. FORCE (FREE-BODY) DIAGRAMS • Because the effect of force depends on both magnitude and direction, force is a vector quantity. • Diagrams that show force vectors as arrows are called free-body diagrams. • Force is measured in units of Newtons. • 1 N = 1kg x 1m/s2

  5. A force diagram, which is also known as a free body diagram, is a sketch in which all the force vectors acting on an object are drawn with their initial points at the center of the object.

  6. Problem 1 • A book is at rest on a table top. Diagram the forces acting on the book. • In this diagram, there are normal and gravitational forces on the book.

  7. ANSWER • In this diagram, there are normal and gravitational forces on the book.

  8. Problem 2 An egg is free-falling from a nest in a tree. Neglect air resistance. Draw a free-body diagram showing the forces involved.

  9. ANSWER Gravity is the only force acting on the egg as it falls.

  10. Balanced Forces • There are 2 cases when all of the forces acting on an object are equal: • 1. When an object is not moving • 2. When an object is moving with constant velocity.

  11. Problem #3 • A man is pulling a sled. The magnitudes of the forces acting on the sled are 60N by the string, 30 N by friction, 90N by the Earth, and 90N upward by the ground. Draw and label the free-body diagram. • Explain how the sled could possibly be moving.

  12. Classwork • Do Page 124 Section Review #’s 1-5

  13. Homework • Complete #’s 1 and 2 under Practice A on Page 124.

  14. Free- Body Diagrams Practice Package

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