Force

1) Force is a push or pull 2) Force is the capacity to do work or cause physical change 3) Force= Mass times acceleration (F = ma)  4) A force is that which changes or tends to change the state of rest or motion of a body. **Examples:** For simplicity sake, all forces (interactions) between objects can be placed into two broad categories: contact forces, and forces resulting from action-at-a-distance. __Contact Forces__ include: frictional forces, buoyant forces, normal forces, and air resistance forces  __Action-at-a-distance forces__ include: gravitation, electrostatic and magnetic forces. **Measuring Force:** Force is measured using either the English System of Measurements or the [|International System of Units (SI).] __Common Units of Force__ --->>__SI__: Newton (N) 1 N = 0.225 lb; One Newton (N) of force is defined as the amount of force needed to accelerate 1 kilogram (kg) of mass at a rate of 1 meter per second squared (m/s2). 1 Newton = 1 kg m/sec2 (A kilogram is the amount of weight at which 1 N of force will accelerate at a rate of 1 m/s2.) --->>__English System__: Pound (LB) 1 LB = 4.448 N <span style="font-family: Arial,Helvetica,sans-serif;"> In English system of measurements, a slug is the amount of mass that 1 pound of force will accelerate at 1 ft/s2, and a pound mass is the amount of mass that 1 LB of force will accelerate at 32 feet/s2. <span style="font-family: Arial,Helvetica,sans-serif;">**Describing a Force:** <span style="font-family: Arial,Helvetica,sans-serif;">A force is a [|vector quantity]. A vector quantity is a quantity which has both magnitude and direction. To fully describe the force acting upon an object, you must describe both its magnitude and direction. Thus, 10 Newtons of force is not a complete description of the force acting on an object. 10 Newtons, downwards is a complete description of the force acting upon an object. <span style="font-family: Arial,Helvetica,sans-serif;">(Note: What is the difference between [|vector and scalar quantities]? A vector has both strength and direction, a scalar quantity can be described using only 1 quantity, magnitude. Examples of scalar quantities are: time, energy and volume since they only represent magnitude and no direction. <span style="font-family: Arial,Helvetica,sans-serif;">**What does applying a Force do?** <span style="font-family: Arial,Helvetica,sans-serif;">Force causes acceleration. <span style="font-family:  Arial,Helvetica,sans-serif;">Newton's Second Law states that: <span style="font-family:  Arial,Helvetica,sans-serif;">the acceleration (a) of an object is directly proportional to the force (F) applied, and inversely proportional to the object's mass (m). <span style="font-family: Arial,Helvetica,sans-serif;"> That means that the more force you apply to an object, the greater the acceleration. And, the more mass the object has, the lower the acceleration. <span style="font-family: Arial,Helvetica,sans-serif;">Newton's Second Law can be written in equation form: F = ma. <span style="font-family: Arial,Helvetica,sans-serif;">For falling objects we can write F=mg where g is the acceleration due to gravity. <span style="font-family: Arial,Helvetica,sans-serif;">The force of gravity is what causes free falling objects to accelerate. These objects all accelerate at the same rate of 9.8 meters/sec^2 <span style="font-family: Arial,Helvetica,sans-serif;">**What is Friction?** <span style="font-family: Arial,Helvetica,sans-serif;">Friction is the force that opposes the relative motion or tendency to such motion of two bodies in contact. If we try to push a block of wood across a table, there are two <span style="font-family: Arial,Helvetica,sans-serif;"> opposing forces that act: the force associated with the push, and a force that is associated with the friction which acts in the opposite direction. As <span style="font-family: Arial,Helvetica,sans-serif;"> frictional forces are decreased (for example, by placing oil on the table) the object moves further and further before stopping. This demonstrates Galileo's law of inertia which states: <span style="font-family: Arial,Helvetica,sans-serif;">an object in a state of motion possesses an ``inertia'' that causes it to remain in that state of motion unless an external force acts on it. <span style="font-family: Arial,Helvetica,sans-serif;">
 * <span style="font-family: Arial,Helvetica,sans-serif;">Definitions for Force: **