# Year 7 Physics

## Forces: Science in Context

Force, within physics, is defined as the term used for an outside influence or action exerted by one body on another body, which produces a change in state of motion or state of configuration; specifically, it produces an acceleration. This limited meaning in science compared to everyday usage is most important because of the specific results of this outside influence.

A force that produces a change in the state of motion of a body gives that body acceleration. If forces acting on a body produces no acceleration, the body will experience some change in configuration: a change of size (longer or shorter), a change of shape (twisted or bent), or a positional change (relative to other masses, charges, or magnets). Changes of size or shape involve elastic properties of materials.

Force. (2014). In K. L. Lerner & B. W. Lerner (Eds.), The Gale Encyclopedia of Science (5th ed.). Farmington Hills, MI: Gale. Retrieved from http://link.galegroup.com/apps/doc/CV2644030927/SCIC?u=61wa_corpus&sid=SCIC&xid=d130b03c

## Gale Virtual Reference Library

Force is a vector, which means it has both magnitude and direction. For example, a force upward with a magnitude of one unit of force is opposite in direction of a downward force that also has one unit of force. In this case, the magnitudes are equal. When several forces act on a body, the forces can be grouped together to produce a net force. English physicist and mathematician Sir Isaac Newton (1642–1727) created his second law of motion that states: A net force (Fnet) acting on a body is related to the mass (m) and acceleration (a) of the body as Fnet = ma. Two forces of equal magnitude, for example, but opposite directions will produce no acceleration. The two forces will cancel each other out for zero acceleration, or a net force of zero. If the body had a velocity before the two forces acted on it, then it will continue to have that same velocity afterwards.

The unit of force in the international system (SI) of units is called the newton, named after Isaac Newton. It is the force that is on an abject with a mass of one kilogram to produce an acceleration of one meter per second squared.

Forces are given various names to indicate some specific character. For example, a wagon can be made to go forward by pushing from behind or pulling from the front so push or pull is more descriptive. Electrical and magnetic forces can result in attraction (tendency to come together) or repulsion (tendency to move apart) but gravitational force results only in attraction of masses. The gravitational force exerted by the Earth, or any other massive body such as a planet, on a body is called weight. A body moving, or attempting to move, over another body experiences a force opposing the motion called friction. When wires, cables, or ropes are stretched, they then in turn exert a force that is called tension. Specific names give information about the nature of the force, what it does, and direction of action.

Force. (2014). In K. L. Lerner & B. W. Lerner (Eds.), The Gale Encyclopedia of Science (5th ed.). Farmington Hills, MI: Gale. Retrieved from http://link.galegroup.com/apps/doc/CV2644030927/SCIC?u=61wa_corpus&sid=SCIC&xid=d130b03c