Applied Force: a push or a pull acting on an object. For example, if a person is pushing on an object, this is an applied force.
Friction Force: a force acting in the opposite direction of an object’s motion. Friction force happens when an object is sliding across a surface.
Gravitational Force (also called Weight): force that attracts two masses. On earth, the force always attracts an object down toward the center of the earth. Because gravitational forces always occur in pairs (Newton’s 3rd Law of Motion), the object pulls the earth upward with an equal force. The earth, being much more massive, doesn’t budge much as a result of this force.
The acceleration due to gravity on earth’s surface is -9.8 m/s2
(can be rounded to -10 m/s2 for easier head math)
(it is negative because it is a downward force)
Normal Force: force exerted by a surface that an object is pushing on. The normal force is perpendicular (at 90 degree angle) to the surface. (“Normal” means perpendicular). When an object pushes against a surface, the surface pushes back. This is an example of Newton’s 3rd Law of Motion: forces occur in equal, opposite pairs.
Air Resistance: Air pushes against an object moving through air. Air resistance force is always in the opposite direction of an object’s velocity. Air resistance increases the faster an object is traveling, Air resistance also depends on the object’s surface area and shape and the density of the air.
Tension Force: When a rope or other object is stretched, it has a tension force. In physics problems where an object is suspended by a string or cable, a tension force acts to hold up that objects.
The above forces are the types that we use in physics problems in our motion unit, but there are other types of forces.
Examples of other forces:
- Forces between charged particles
- Forces involving magnetic fields
- Forces involved in nuclear processes