# Motion—Forces at Work

```Motion—Forces at Work
position: a certain place relative to another object or the background; (tracing and
measuring an object’s position over time can describe its motion)
motion: a change of position; (unless acted on by a force, objects in motion tend to stay
in motion and objects at rest remain at rest)
inertia: any object stays still or moves in the same way until a force acts upon it
frame of reference: the things around you that you can sense and use to describe motion
speed: a measure of an object’s change in position during a unit of time; (how fast an
object is moving); for example, 10 meters per second or 50 miles per hour; (a line graph
can be used to show an object’s speed over time)
force: a push or pull that causes an object to move, stop, or change speed or direction;
(the greater the force, the greater the change in motion; the bigger the object, the less
effect a force will have upon it)
work: the use of a force to move an object; (moving an object a distance through space)
Newton: the metric unit of force
gravity: a force that pulls all objects toward each other
friction: a force that keeps objects that are touching each other from sliding past each
other easily; it is the resistance of motion; (friction creates heat)
energy: the ability to cause a change; (exists in two states: kinetic or “motion energy”
and potential or “stored energy”)
kinetic energy: the energy of motion; (an object that is in motion)
potential energy: stored energy; (an object that is NOT in motion)
forms of energy:
1. Chemical – stored energy in matter (like in food or fuel)
2. Electrical – result of electricity (electrical energy can be transformed into
heat, light or mechanical energy)
3. Mechanical – energy associated with the motion of an object through work
(ex: can opener)
4. Solar – energy from the sun
```