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energy - the ability to do work 

work - that which is when a force acts on matter and changes it direction

force - that which produces or prevents motion; that which can impose a change of velocity on a material

motion - a continuing change of place or position

uniform motion - moving in a straight line at a constant speed

delta - the change in or difference between (symbol is D)

displacement - a change in position; Dd = d₂ – d₁

potential energy - stored energy due to composition, position, or condition

kinetic energy -work done by a force along a given displacement; the energy involved in motion

work

power - work divided by time; time required to exert force over a distance

gravity - that attractive force existing between all objects in the Universe

gravitational acceleration   9.8 m/s², or 32 ft/s², or 980 cm/s²

velocity -  the rate of change of displacement over time; the ratio of motion in a particular direction;   the distance traveled divided by the time taken        (average velocity = Ad/At)

acceleration - the rate of change of velocity over time (average acceleration = AV/At)

scalar quantities - quantities involving only a given magnitude (examples: temperature, time, mass)

vector quantities -  quantities which require both a magnitude and a given direction (for a complete description, examples: displacement, velocity, force, acceleration)

 inertia -    the reluctance of all matter to change its state of rest or uniform motion; the tendency of all objects to preserve its motion

mass -     a measure of the inertia of that object; the greater the resistance something offers to being set in motion the greater its mass.   The amount of matter being a definition for mass is a poor one.

FRICTION

 Inertia refers to the fact that bodies maintain their original state of rest or motion in the absence of any net forces acting on them; but even a small force is enough to accelerate a body despite the inertia.

 Friction -  refers to the actual forces that come into begin when 2 forces are in contact that act to oppose motion between them

 Sliding friction - this is the frictional resistance an object in motion experiences

 Static friction -      this is the frictional resistance a stationary object must overcome in order to be set in motion

 Rolling friction - wheels exhibit this form of friction (which is usually less than sliding friction)

 Lubricants -         reduce friction by separating two contacting surfaces with an intermediate layer of softer material

FORCES

 A force is any influence that can produce a change in the velocity of an object. This definition goes further than `push' or `pull' in that no direct contact is necessarily implied

 A force acting on a body may increase or decrease its speed and or change its direction. A force may move the particles of which a body is composed and thus change its shape.

 A force is a vector quantity.

 A newton is a unit of force which when acting along, causes a 1 kg mass to accelerate at a rate of 1 m/s per second. Think of the relationship that an average size apple on your hand exerts about a newton of force.

 A kg of mass has a weight of 9.8 newton (about 2.4 pounds).

 A newton = 0.225 lb (a little less than ¼ of a pound)

 

1 slug = 32 pounds of butter

 When 2 or more forces act upon an' object without affecting its state of motion, the forces cancel one another out; this is called balanced forces and the object is in equilibrium.

 For a velocity change, a net force, or unbalanced force is required. This force is capable of accelerating the object.

 Force problems:

 1) Boy A is pulling on a rope eastward at 40 newtons of force and Boy B joins him pulling eastward at 60 newtons. What is the resultant force?

2) Girl A is pulling eastward at 40 lb while Girl B is pulling westward at 60 lb. The resultant or net force would be?

 

3) Boy A is pulling eastward at 40 N of force while Girl B pulls southward with a force of 30 N.  What is the net force (give both magnitude and direction)?