forces and motion

force

a push or pull exerted on an object

balanced forces

equal forces acting on an object in opposite directions

unbalanced forces

forces that produce a nonzero net force which changes an object's motion

net force

the overall force on an object when all the individual forces acting on it are added together

free-body diagram

a picture with arrows (vectors) showing all of the forces acting on an object and the magnitude of those forces relative to each other

magnitude

the size of a force represented by the length of an arrow (vector) or a numerical measurement

contact force

when one object pushes or pulls another object by touching it; the first object is applying force to the second (e.g. a person pushing a box)

non-contact force

when one object pushes or pulls another object without touching; two objects are affected by a field around one of the objects such as a magnetic or electrical field (e.g. magnets attracting or repelling each other)

motion

the state in which one object's distance from another is changing

reference point

a place or object used for comparison to determine if an object is in motion

speed

the distance an object travels per unit of time

velocity

speed in a given direction

acceleration

the rate at which velocity and/or direction changes

inertia

the tendency of an object to resist any change in its motion

vector

an arrow representing magnitude and direction of forces; the length of the arrow equals its magnitude and the arrow itself shows the direction of that magnitude

relative motion

motion of moving objects with respect to other moving or stationary objects, also known as apparent motion

friction

the force that one surface exerts on another when the two surfaces or substances make contact with each other

air resistance (drag)

the fluid friction experienced by objects falling through air

gravity

the force that pulls objects toward each other, the force is proportional to the mass of each object involved and the distance between the objects (if the objects are closer, the force is stronger; if an object has more mass, it will have more gravitational force)