Air Resistance and Free Fall
When an object is under the influenc of gravity when falling, it is said to be in free fall. Many factors influence the air resistance acting upon the object in free fall. When an object is in free fall the air resistance will begin to increase, the net force decreasing. The magnitude of air resistance will become great enough that it equals the magnitude of the force of gravity, the object will then be moving at a constant speed. This maximum constant speed of the free falling object is called terminal speed (terminal velocity).
Friction
An object will not move initially due to static friction. Static friction (Fs) is the force exerted on a stationary object by a surface that prevents the object from starting to move. The applied force must be large enough to overcome the static friction in order for the object to move. Kinetic friction (Fk) is the force exerted on a moving object by a surface, and acts opposite to the direction of motion. The friction graph (left) shows the magnitude of the friction versus the appiled force. Once the object begins motion, the friction suddenly drops.
The coefficient of friction is the ratio of magnitude of the force of friction, acting on an object to the magnitude of the normal force acting on the object. As with friction, there is a coefficient of static friction (Us) and coefficient of kinetic friction (Uk). Since the maximum force of static friction is usually greater than the kinetic frriction, the coefficient of static friction is usually greater than the coefficient of kinetic friction. The equations for each are:
Practice
Quizzes/ Worksheets
1. https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxtcnRyYXNrc3BoeXNpY3N8Z3g6MmE3MmZmYzY2M2VlMDZkMQ (practice problems- solutions below)
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxtcnRyYXNrc3BoeXNpY3N8Z3g6NGYzM2NlMjJlZjY4MWZhNg (SOLUTIONS)
2. http://www.stmary.ws/highschool/physics/home/marys_java/gravity_friction_momentum/frictionQuiz.html (friction multiple choice)
3. http://home.comcast.net/~drewpoche/PHYSICS/Physics_1_Assignments_Tests_S1_files/Set%203%20with%20key.pdf (coefficient of friction worksheet)
4. http://www.hayshighindians.com/academics/classes/csadams/srphysics/mechanics/Friction%20problems.pdf (friction worksheet)
Simulation
1. http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=27&ClassID=2057186 (friction on inclined plane, gizmo)
1. https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxtcnRyYXNrc3BoeXNpY3N8Z3g6MmE3MmZmYzY2M2VlMDZkMQ (practice problems- solutions below)
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxtcnRyYXNrc3BoeXNpY3N8Z3g6NGYzM2NlMjJlZjY4MWZhNg (SOLUTIONS)
2. http://www.stmary.ws/highschool/physics/home/marys_java/gravity_friction_momentum/frictionQuiz.html (friction multiple choice)
3. http://home.comcast.net/~drewpoche/PHYSICS/Physics_1_Assignments_Tests_S1_files/Set%203%20with%20key.pdf (coefficient of friction worksheet)
4. http://www.hayshighindians.com/academics/classes/csadams/srphysics/mechanics/Friction%20problems.pdf (friction worksheet)
Simulation
1. http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=27&ClassID=2057186 (friction on inclined plane, gizmo)