Force
Force, in physics, any
action or influence that accelerates an object. Force is a vector, which means
that it has both direction and magnitude. When several forces act on an object,
the forces can be combined to give a net force. The net force acting on
an object, the object's mass, and the acceleration of the object are all related
to each other by Newton's second law of motion, named after English physicist
and mathematician Isaac Newton. The second law of motion states that the
acceleration an object experiences multiplied by the mass of the object is equal
to the net force acting on an object. Thus, if a given force acts on two objects
of different mass, the object with a larger mass will have a lower acceleration.
See Mechanics.
An object experiences a force when it is pushed or pulled
by another object. For example, shoving a stationary shopping cart applies a
force that causes the shopping cart to accelerate. An object can also experience
a force because of the influence of a field. For example, a dropped ball
accelerates toward the ground because of the presence of the gravitational field
(see Gravitation); electrical charges attract or repel each other because
of the presence of an electric field (see Electricity).
Usually, several forces act on an object at once. If
multiple forces combine to give a net force that is zero, then the object will
not accelerate; the object will either remain motionless or continue moving at a
constant velocity. For example, if a person pushes a shopping cart with a force
equal in magnitude to the force of friction that opposes the cart's motion, the
forces will cancel, giving a net force of zero. As a result, the cart will move
down the aisle with a constant velocity. If the person suddenly stops pushing
the cart, the only force acting on the cart is the frictional force. Since the
net force is no longer zero, the cart accelerates: its velocity drops to
zero.
In the international system of units, the unit of force is
the newton, which is the force that imparts to an object with a mass of 1
kg an acceleration of 1 m/sec2. In English units, the unit of force
is the poundal, which is the amount of force that accelerates a 1-lb
object 1 ft/sec2.
Forces acting at the molecular and atomic level are also
known as interactions. See also Elementary Particles.
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