Transcript Forces
Forces Force: A push or a pull on an object. A vector quantity. Two Types of Forces: Contact Forces: When the object is directly pushed or pulled. Field Forces: When the object is not ‘touched’. Free Body Diagrams When working with forces, it is helpful to use a free body diagram. It’s simply a drawing that includes the forces acting on a system. Combining Forces When two or more forces act on an object, they can be combined / simplified into one force. This is known as the Net Force. If the net force on an object is zero, the object is said to be in Equilibrium, or Static. What is the net force in each of the situations below? Sir Isaac Newton First person to relate force to motion. Has three laws bearing his name. Newton’s First Law: An object in motion will remain in motion and an object at rest will remain at rest unless a force acts upon it. Also known as the Law of Inertia Inertia: The tendency of an object to resist change. More mass = more inertia. Newton’s Second Law: The acceleration of an object is directly proportional to the net force acting on it and indirectly proportional to it’s mass. F = ma Newton’s Third Law: For every action, there is an equal and opposite reaction. (1642-1727) Since F = ma, the units of force are mass times acceleration, or kg m This is also known as a Newton (N). Example Problem: Three confused sled dogs are trying to pull a sled across the Alaskan snow. Alutia pulls east with a force of 35 N, Seward also pulls east but with a force of 42 N, and Kodiak pulls west with a force of 53 N. A) What is the net force on the sled? B) Ignoring friction, with what acceleration can the dogs propel the 113 kg sled? C) With this acceleration, how fast can they cover 100. m from a dead stop? s2 Example Problems Common Forces We’ll Be Encountering This Year Weight vs. Mass Mass is a scalar quantity. Weight is a vector or Force quantity. It depends on acceleration. SI English Mass Kg lb Weight N lbf Your mass on earth is the same as your mass on the moon. Your weight on earth is different than your weight on the moon. Weight depends on the acceleration due to gravity. Example Problem 2 Drag Force: A force exerted by a fluid on an object in the opposite direction of motion. http://www.boreme.com/boreme/funny-2006/tomahawk-p1.php Terminal Velocity: The constant velocity that is reached when the drag force equals the force of gravity. A 50.0 kg bucket is being lifted by a rope. The rope will not break if the tension is 525 N or less. The bucket started at rest, and after being lifted 3.0 m, it is moving at 3.0 m/s. If the acceleration is constant, is the rope in danger of breaking?