Types of Forces
In kinematics we learned how objects move, forces, instead look at why the objects move. Dynamics, is the study of the causes of motion. Newtons are the SI unit of force (1 N = 1 kg x m/s2). To understand a force situation, FBDs, free-body diagrams, simple drawings of an object and all the forces involved. A System Diagram, is a simple sketch of the objects involved.
When drawing FBDs, all forces acting on the object need to be taken into account. The applied force (Fa) is a force that results when one object makes contact with another and pushes or pulls on it. Another possible force is tension (Ft). Tension is a pulling force from a rope or string on an object that always points forward the rope or string. Whenever an object is in contact with a surface, the surface can exert two different forces on it. The normal force (Fn) is a perpendicular force on an object in contact with the surface. It always points away from the surface. The other force exerted by a surface is friction (Ff). Friction opposes the sliding of two surfaces across one another, it acts opposite to the motion or attempted motion. The force of gravity (Fg- also called gravitational force) is an act at a distance force. It is the force of attraction between any two objects. To calculate the magnitude of the force of gravity we can use the following:
Gravity is -9.81m/s/s and meausred in newtons, while the mass (m) is measured in kg.
Net Force
Many force problems require you to sum all the force acting upon the object. This total force is called the net force (Fnet) or resultant force. The net force can be calculated using FBDs.
Practice
Quizzes/Worksheets
1. http://www.physicsclassroom.com/shwave/fbd.cfm (interactive practice problems)
2. http://www.ck12.org/concept/Free-Body-Diagrams/?ref=%2Fconcept%2FFree-Body-Diagrams%2F#view_exercises (multiple choice/true and false)
3. http://www.batesville.k12.in.us/physics/phynet/mechanics/newton1/the_net_force.html (true and false/multiple choice)
1. http://www.physicsclassroom.com/shwave/fbd.cfm (interactive practice problems)
2. http://www.ck12.org/concept/Free-Body-Diagrams/?ref=%2Fconcept%2FFree-Body-Diagrams%2F#view_exercises (multiple choice/true and false)
3. http://www.batesville.k12.in.us/physics/phynet/mechanics/newton1/the_net_force.html (true and false/multiple choice)