10.1 What We Mean By Force 253
10.1 What We Mean By Force
What is force? The simplest form of a force that represents the interaction of two objects is a push
or a pull. When you push or pull on a lawn mower or on a vacuum cleaner, thatinteraction between
your hand and the lawn moweror the vacuum cleaner is calledforce. When anautomobile pulls a
U-Haul trailer, a force is exerted by the bumper hitch on the trailer (see Figure 10.1). The inter-
action representing the trailer being pulled by the bumper hitch is represented by a force. In these
examples, the force is exerted by one body on another body by direct contact. Not all forces result
from direct contact. For example, gravitational and magnetic forces are not exerted by direct con-
tact. If you hold your book, say, 3 feet above the ground and let it go, what happens? It falls; that
is due to gravitational force which is exerted by the earth on the book. The gravitational attrac-
tive forces act at a distance. A satellite orbiting the earth is continuously being pulled by the earth
toward the center of the earth, and this allows the satellite to maintain its orbit. We will discuss
the universal law of gravitational attraction in detail later. All forces, whether they represent the
interaction of two bodies in direct contact or the interaction of two bodies at a distance (gravita-
tional force), are defined by their magnitudes, their directions, and the points of application.(a)
(b)
■Figure 10.1 (a) Force
exerted by your hand on a lawn
mower, (b) Force exerted by
bumper hitch on the trailerSource:ARENA Creative /
ShutterstockSource:Robert J. Beyers II /
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