Law I Part 2 – The second part of Newton’s 1st Law is the idea of forces causing changes in motion or velocity. Here, Newton is referring to the net or sum of all the forces. Net force equation: Fnet = F1 + F2 + F3 +… The unit for force is the Newton, N, and forces are vector quantities. What the first law is saying is there are basically only two cases for motion: Uniform Motion (constant velocity) case, when Fnet = 0 Non-Uniform Motion (changing velocity/acceleration), when Fnet 0 ***Note that a net force of zero does not mean no forces are acting on an object. There can be forces acting on an object where the net force is zero, as long as the forces balance each other. Conversely, the presence of a net force is an indication of an unbalanced set of forces. Example 2: Indicate whether the forces are balanced or unbalanced acting on a chalkduster on a blackboard ledge that is: At rest? Pushed by a hand and then let go? ___________ Pushed by a hand at constant velocity across the ledge? __________ Since forces are vectors, if two or more forces act on an object, the forces must be added vectorally to produce the net balanced or unbalanced force. Example 3: Three forces of equal magnitude 10.0 N act on an object. What is the net force (magnitude and direction) if the direction of the forces is given by: F1 is east, F2 is west, and F3 is west F1 is east, F2 is north, and F3 is east
Law I – Part 2 The second part of Newton’s 1st Law is the idea of forces causing changes in motion or velocity. Here, Newton is referring to the net or sum of all the forces. Net force equation: Fnet = F1 + F2 + F3 +… The unit for force is the Newton, N, and forces are vector quantities. What the first law is saying is there are basically only two cases for motion: Uniform Motion (constant velocity) case, when Fnet = 0 Non-Uniform Motion (changing velocity/acceleration), when Fnet 0 ***Note that a net force of zero does not mean no forces are acting on an object. There can be forces acting on an object where the net force is zero, as long as the forces balance each other. Conversely, the presence of a net force is an indication of an unbalanced set of forces. Example 2: Indicate whether the forces are balanced or unbalanced acting on a chalkduster on a blackboard ledge that is: At rest? Pushed by a hand and then let go? ___________ Pushed by a hand at constant velocity across the ledge? __________ Since forces are vectors, if two or more forces act on an object, the forces must be added vectorally to produce the net balanced or unbalanced force. Example 3: Three forces of equal magnitude 10.0 N act on an object. What is the net force (magnitude and direction) if the direction of the forces is given by: F1 is east, F2 is west, and F3 is west F1 is east, F2 is north, and F3 is east
Unit%20B-Dynamics%20student%20notes.docx