# Computer Understanding of Physics Problems Stated in Natural Language

Gordon S. Novak Jr.
American Journal of Computational Linguistics,
Microfiche 53, 1976.

## Abstract

This thesis describes a computer program, called ISAAC, which can
read, understand, solve, and draw pictures of physics problems stated
in English. The program has solved twenty problems, most of which were
taken unedited from high school and college physics texts. These
problems involve rigid bodies in static equilibrium, and include such
objects as levers, pivots, weights, ropes, and springs in various
configurations. An example of the class of problems solved is the
following (from * Schaum's Outline of College Physics*):
The foot of a ladder rests against a vertical wall and on a
horizontal floor. The top of the ladder is supported from the wall by
a horizontal rope 30 ft long. The ladder is 50 ft long, weighs 100 lb
with its center of gravity 20 ft from the foot, and a 150 lb man is 10
ft from the top. Determine the tension in the rope.

In order to understand such a problem, it is necessary to build an
internal model of the problem in which the various objects and their
interrelationships are adequately represented. Many of the
relationships and features of the objects are not specified explicitly
in the problem statement, but must be inferred by using common sense
knowledge of what is usual. In the above example, we assume that the
man is standing on the ladder, although this is not explicitly stated.
Thus, the understanding of a physics problem is an active process in
which the sentences of the problem statement are used to guide the
construction of a model which represents the relationships and
features of objects with much greater detail and specificity than
they are specified in the original problem statement.
In this thesis, we investigate ways in which the meanings of phrases
and sentences may be understood and related to a developing model of
the problem, using common sense knowledge (represented by computer
programs) to aid the understanding process. Ways of representing
objects and their relationships are developed. These representations,
which are originally created in response to the sentences in the
problem statement, are further elaborated by processes which construct
a geometric model of the problem, associate canonical objects (such as
a point mass) with physical objects (such as a person), write and
solve equations which describe the interactions of the objects, and
construct a diagram of the problem.

The techniques used in ISAAC have potential application in providing a
natural language interface between specialist programs and users who
are not computer professionals, and in computer programs for teaching
physics and other technical subjects.

On-line Demonstration of Isaac:
Solve Physics Problems stated in English.