Force

Force changes the acceleration of an object. For example, when we hit a baseball the
acceleration of the ball is changed because we applied force (in the form of swinging a
bat) to the ball. If the ball was pitched to us, then it had a positive acceleration coming
toward us; when we hit it we changed the acceleration to the negative direction.
Force is a very important concept in physics. This is understandable because it is
constantly in effect. For example, even when we are sitting down there is a force of
gravity keeping us in the chair. The first example with the baseball is considered contact
force, as an object (the bat) made contact with the ball to make it change its acceleration.
Gravity is considered a field force (or a force-at-a-distance) because it does not have to
have contact with the object while applying force. Gravity causes items to be drawn to
the Earth’s core. This is why we can sit (and stand) and not float about. This is why we
have weight. It is all because of gravity. If there were an object on the floor it would be
sitting on the floor because of gravity. If we tried to pick it up, we would have to apply
enough force to counteract the force that gravity is applying to it. In outer space, objects
float around and are very light because regardless of their mass (assuming it is not as large
as a planet) they do not weigh much at all because there is no force pushing them down.
Mass is the amount of physical matter an object comprises. With the force of gravity our
mass has weight. The more mass an object has, the more it weighs on Earth. The larger
the mass, the more force is applied against that object to bring it toward the Earth’s core.
When we try to move an object, we have to apply enough force to accelerate the object.
CHAPTER 294 14 Physics Basics
If we do not apply as much force to lift the object upward as gravity is applying to the
object downward, the object will not move.
Newton’s Second Law of Motion describes the relationship between an object’s mass and
acceleration with the force applied to the object. The formula is:
F = ma
We know that acceleration is a vector, and force is a vector as well. This makes sense as we
think about the fact that when we hit that baseball it can go in multiple directions (pop
fly, foul ball, etc.). This is because we are creating acceleration when we apply force to the
object at different angles. Our mass is a scalar value (one dimension) and not a vector
(multiple dimensions). We could also write the preceding formula as:
a = F/m
In our previous code example we had an invisible force acting on our sphere that was
generating the acceleration of the sphere. Newton’s First Law of Motion basically states
that objects that are in motion stay in motion and objects that are sitting still stay still.
Our previous demo shows this as well, as if we do not press any keys to accelerate our
sphere it stays at rest. Once we do apply some force to the object, it accelerates and stays
in motion.