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1D Kinematics: Nuts & Bolts

1D Kinematics: Nuts & Bolts

3. Nuts & Bolts

Algorithm

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  1. Read and re-read the whole problem carefully.
  2. Visualize the scenario. Mentally try to understand what the object is doing.
    1. Motion diagrams are a great tool here for visual cues as to what the motion of an object looks like.
  3. Draw a physical representation of the scenario; include initial and final velocity vectors, acceleration vectors, position vectors, and displacement vectors.
  4. Define a coordinate system; place the origin on the physical representation where you want the zero location of the x and y components of position.
  5. Identify and write down the knowns and unknowns.
  6. Identify and write down any connecting pieces of information.
  7. Determine which kinematic equation(s) will provide you with the proper ratio of equations to number of unknowns; you need at least the same number of unique equations as unknowns to be able to solve for an unknown.
  8. Carry out the algebraic process of solving the equation(s).
    1. If simple, desired unknown can be directly solved for.
    2. May have to solve for intermediate unknown to solve for desired known.
    3. May have to solve multiple equations and multiple unknowns.
    4. May have to refer to the geometry to create another equation.
    5. If multiple objects or constant acceleration stages or dimensions, there is a set of kinematic equations for each. Something will connect them.
  9. Evaluate your answer, make sure units are correct and the results are within reason.

Multiple Representations

Multiple Representations is the idea that a physical phenomena can be explored in many different ways. For example, there is the physical representation which models the system with figures and diagrams, such as a free body diagram. There is also the mathematical representation which uses the equation(s) governing the physics of the system. All of the representations can be used together to help us understand and quantify the physical phenomena.

 

Observe the different types of representations for this section below;

Physical Representation

Physical Representations explain the features of the situation in a visual way, often with vector representations of physical quantities overlaid a simple diagram or picture of the situation.

Kinematics problems are often analyzed with physical descriptions. Below we have an object launched from a ledge with initial horizontal and vertical velocity components. The vectors indicate the relative magnitudes of the horizontal and vertial velocity components at different stages of the objects motion.

In addition, simple 1D motion diagrams are utilized to describe the speed of an object and whether or not the object has any acceleration.

Mathematical Representation

Mathematical Representation uses equation(s) to describe the situation.

Main kinematics equations. Notice that we use $ r $ to represent the vector position. In the videos below, Professor Matt Anderson uses $ x $ and $ y $ to denote position in a given coordinate direction.

$ \vec{r}_{f} = \vec{r}_{i}+\vec{v}_{i} \Delta t + \frac{1}{2} \vec{a} \Delta t^{2} $

$ \vec{v}_{f} = \vec{v}_{i} + \vec{a} \Delta t $

$ v_{fx}^{2} = v_{ix}^{2}+2a_{x} \Delta x $

Watch Professor Matt Anderson explain 1D and 2D Kinematics equations using the mathematical representation.

Video 1: Kinematics equations in 1D

Video 2: Kinematics equations in 2D

Graphical Representation

Graphical Representation describes the situation through use of plots and graphs.

 

the Physics Classroom introduces the relationship between kinematics equations and their graphical representation. In addition, for a more indepth discussion please refer to the graphical anaysis section.

Descriptive Representation

Descriptive Representation is made up entirely of words or annotations. Think about how you might explain the situation to someone else.

The branch of mechanics concerned with the motion of objects without reference to the forces that cause the motion.

Actual Representation

Actual Phenomena could be thought of as doing the experiment.

For example, a person throws a ball upward into the air with an initial velocity of $15.0 \frac{m}{s}$. You can calculate how high it goes and how long the ball is in the air before it comes back to your hand. Ignore air resistance.


Example Problems

Set 1: RedKnightPhysics, Problems 1-16

Set 2: Hyperphysics motion examples

For additional practice problems and worked examples, go here.