Forces and Motion Terms
Space
We’re all in space. No, not in the universe, floating away from everything we’ve ever known and loved. Space is that reality continuance thingy with three dimensions that we navigate everyday while walking up the street. Space is a location with spatial coordinates.Time
Ever heard the line Time is of the essence? Before waxing philosophical, just know that time is essential to describe any kind of physics because interactions take place over time the same way they take place over space. It’s the invisible dimension that gives duration to an event.Spacetime
Spacetime = space + time = rendezvous. If we’re planning on meeting friends, then we give them a place (space) and a time at which to meet up. Without the proper space AND time coordinates, we’ll never meet one another, because all events take place within the spacetime continuum.Dimension
Walk into a movie. Do they make you put on those horribly cheesy glasses? If yes, the movie is in 3D, just like the rest of the world with its up, over and out-there-in-your-face-ness. If not, then the movie is confined to the screen, in 2D. The “forward and backward”-ness of moving through a row of seats in the theatre is bounded by one spatial dimension, in 1D.Distance
The amount of spatial dimension between two places. Let’s say we walk to the movie theatre, which is a block away on foot and then after the movie, we walk back home. The total round-trip distance walked is therefore two blocks.SI Unit
The standard international unit of whatever type of variable is being measured, such as meters for distance or kilograms for mass. Use alternate units at the peril of your grade.Displacement
The amount of spatial dimension between the thing that moves and its starting point. The distance traveled from home to the theatre and back might be two blocks, but our total displacement is zero, since we end up right back where we started. Displacement refers to a specific place. Oh, and it’s a vector quantity.Speed
A rate of distance per time, just as recorded by the speedometer of a car in units of miles per hour.Velocity
This is speed, but with a direction. It’s distance divided by time, pointing towards the movie theatre (or home again).Acceleration
The change in velocity over time. If velocity changes, it means something’s either speeding up, slowing down, changing direction, or some combination thereof. Exciting changes, all. Amusement parks build their thrills off of acceleration.Inertial Mass
The ratio of the applied force to an object’s rotational acceleration, in SI units of kilograms. It’s related to but not equal to weight. It quantifies how difficult it is to make something spin.Mass
The amount of “stuff” in an object, given as a ratio of an object’s gravitational force (weight) to its gravitational acceleration. Also known as a property of matter. Mass is constant. So, when we start eating gallons of ice cream every day, the mass of the universe will remain constant, even if an extra bit of that is attached to us.Scalar
A quantity of something. Could be anything. The number of words in this module is a scalar, but if we read them in any direction or order, we’ll be confused.Vector
A scalar with direction, represented by an arrow in space. Directions are endlessly useful, as we’ve likely discovered without the help of a physics class. For example, we can’t read this module by reading any word in any order, unless we’re masochistic.Force
A source of motion. Think of a force like a great influence in your life. You tend to value what that person says enough for it to advise your behavior. Forces are responsible for all changes in motion. A force is like an influential friend who has telekinesis powers, but as a vector quantity.Newton’s First Law Of Motion
Objects are like people. Once they get comfy, they don’t want to move either. If you’re resting, you’ll have a tendency to keep resting. Objects that are uninfluenced by external forces always either remain at rest or continue moving at a constant velocity. This is the law of inertia, or the “couch potato law” for the motionless.Newton’s Second Law Of Motion
F = ma. The force applied on an object is equal to its mass times its acceleration. If an object ‘‘accelerates, it’s is experiencing a force. If the object isn’t moving then F = 0. If it’s moving but going at a constant speed, then F is also zero. When the total net force on the object is zero, the system is at equilibrium, a kind of boring state where not much happens and old, stiff substitute teachers from 80’s movies our parents probably liked, call out “Bueller, Bueller.”Newton’s Third Law Of Motion
For every action, there’s an equal and opposite reaction, such as our force pushing on a wall countered by the wall pushing back on our hands. That’s not to say that objects can’t move: they do all the time. Objects’ motions are governed by the forces acting on them, and not their own reactions back.Acceleration Of Gravity
the acceleration due to a gravitational force. On the surface of planet Earth, this acceleration is
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