Recognizing Forces - Questions 7 Help

Forces are pushes or pulls that act on an object as the result of that object (the system) interacting with other objects (the surroundings). These pushes and pulls are most fully described by sentences like "The floor pushes upwards on the object as the result of the object pushing downward on the floor." A common practice is to shorten the lengthy description by replacing the description with a name like "normal force". Applying an understanding of force types allows one to determine what types of forces are acting on an object.

It is common to describe the forces acting upon an object as being of a given type. The listing below describes the most common force types. In this question, an object is sliding or skidding across a surface. Use this description and an understanding of the force types to identify which force types act upon the object:

Force Types

Normal Force: A normal force exists whenever two surfaces are pressed against one another. Sit on a chair, stand on the floor, lean against the wall ... in all cases your body and another surface are pressing against each other. This pressing together results in a force on your body (and on the object). This is called a normal force. The normal force exists when two objects are pressed together ... even if one of the objects is moving across the surface of the other.

Gravity Force: Gravity falls into the category of a non-contact force. It is the result of the interaction between two masses. All objects with mass attract. And when the Earth or some other very massive object is present, the gravity force is significant in size. For an object on Earth, you can always count on this force being present.

Applied Force: This force is the result of person pushing or pulling on an object. A careful reading of the description of the situation will often describe a person "applying a force." This force could be considered a sub-type of the normal force. For our purposes, we will think of the applied force resulting when another person is doing the pushing or pulling on the object.

Friction Force: Friction force results when two touching surfaces are sliding across each other (sliding friction) or attempting to slide across each other (static friction). Read the problem carefully to determine if the object's surface is in contact with another surface. Then determine if the object is moving across the surface; if it is, then there is a sliding friction force. Or determine if the object is stationary on an inclined surface; if it is, then there is a static friction force holding it in place.

Tension Force: Tension is the force that results when a rope, string, cable, or wire is attached to an object and exerting a push or pull on the object. Read the description of the situation carefully and look for words that describe a rope, wire, string, or cable pulling on the object.

Air Resistance Force: Air resistance results when there is relative motion between the object and the surrounding air. This force is caused by the collisions between air particles and the moving object. Whenever an object is moving (and there is air present around it), there will be an air resistance force.