What is kinematics? Physics answers made simple

academics High School kinematics physics
By Jacob

How to use this guide

This blog post is the first in a series on how to understand and approach kinematics problems. It is meant to supplement your class and textbook. I will focus on practical applications, how to solve problems, and common mistakes that students make. If you want to learn the basics of kinematics, I recommend a textbook, but if you want to gain a deeper understanding, avoid confusion and learn how to approach problems, take the red pill and join us! 

What is kinematics?

Kinematics is simply the study of motion. This is literally what the word means: kinesis (motion) + tics (the study of. Think mathematics, politics, pizzatics). On a more practical level, the kinematics you learn in your intro physics class is the study of position, velocity, and momentum. On the most practical level, kinematics is the study of what happens when you toss a ball. Which means, if you can toss a ball, you can learn kinematics – FYI, as anyone who has ever seen me play sports knows, the reverse is not true.

Position, Velocity, and Acceleration

So kinematics is the study of three things, but what exactly are those three things?

Position:

Where an object is. It’s location. Physics problems will refer to this as x, y, z p, r, or d. Every teacher has their preferences, so learn yours, but for this blog we will use x and y. We are also often interested in the change in position, known as displacement, which is referred to as Δx, Δy, Δp, Δd or sometimes just x, y, or d to make things confusing. Position and displacement are usually measured in meters or m.

Velocity:

How fast an object is moving and in what direction: aka how the distance is changing over time. Physics problems will almost always refer to velocity as v. Velocity is usually measured in meters per second, or m/s. When velocity is constant, it can be described by the equation v=Δx/Δt (the change in position divided by the change in time).

Acceleration:

How the velocity of the object is changing. If a Ferrari goes from 0 to 60mph in 2.4 seconds then it is accelerating. If it the driver freaks out and crashes into a wall that stops the car, then it has also accelerated. Acceleration is always referred to as a, and is measured in meters per second per second, or m/s2.

When acceleration is constant, it can be is described by the equation a=Δv/Δt (the change in position divided by the change in time). You might notice that this equation is very similar to the equation for velocity. That is not a coincidence: it reflects the vast underlying physics that determines everything in the world. 

Avoid Common Mistakes: Position, Distance, and Displacement

Position, Displacement and Distance are easy to confuse and physics teachers often test to make sure you understand the difference. Position is measured from some origin point and defines the location of the object - in kinematics, we often define the origin point as the starting location of the object to make things easier. Distance measures the total distance an object has traveled. Displacement measures how far an object is from where it started.

To understand the difference, imagine a scenario where you start 3 meters to the right of the origin and walk 2 meters left, then 4 meters right. Your position at the beginning is 3 meters, and at the end it is 5 meters. Your distance is 6 meters because that’s how far you walked. Your displacement at the end, however, is 2 meters because you are only 2 meters away from where you started.

Screen Shot 2017-02-08 at 5.07.51 PM.png

Avoid Common Mistakes: Velocity and Speed

In regular life we use the words velocity and speed interchangeably, but in physics we never do. Speed is how fast something moves, velocity is how fast it moves AND in what direction (we call this concept of magnitude+direction a vector). That means an object can change velocity without changing speed, for examples a car going around a circular track. It also means that speed can increase while velocity decreases. If velocity is negative and acceleration is negative then the velocity will be a more and more negative number, so velocity will decrease (go from -60 m/s to -120 m/s) but speed will increase (go from 60 m/s to 120 m/s). 

Avoid Common Mistakes: Acceleration and Velocity

Students new to physics are often puzzled by the idea that acceleration and velocity can go in different directions. When an object accelerates it should go faster, right? Not necessarily. For example, if you throw an object in the air, it starts with a positive, upward velocity but the acceleration is negative and downward. Eventually, the object stops going up and falls back to the ground, at which point the acceleration and the velocity are in the same direction. However, at any given moment the acceleration can be in any direction – acceleration determines the change in velocity NOT the velocity itself. 

Conclusion

So now we understand the basics of kinematics, but how do we use them? In my next blog, I will cover the standard equations of kinematics and how to use them to solve problems in 1-Dimension.

Comments

topicTopics
academics study skills MCAT medical school admissions SAT expository writing college admissions English MD/PhD admissions strategy writing LSAT GMAT GRE physics chemistry math biology graduate admissions academic advice ACT interview prep law school admissions test anxiety language learning premed MBA admissions career advice personal statements homework help AP exams creative writing MD study schedules test prep computer science Common Application summer activities history mathematics philosophy organic chemistry secondary applications economics supplements research 1L PSAT admissions coaching grammar law psychology statistics & probability legal studies ESL CARS SSAT covid-19 dental admissions logic games reading comprehension engineering USMLE calculus PhD admissions Spanish mentorship parents Latin biochemistry case coaching verbal reasoning DAT English literature STEM excel medical school political science skills AMCAS French Linguistics MBA coursework Tutoring Approaches academic integrity chinese letters of recommendation Anki DO Social Advocacy admissions advice algebra art history artificial intelligence astrophysics business cell biology classics diversity statement gap year genetics geometry kinematics linear algebra mechanical engineering mental health presentations quantitative reasoning study abroad technical interviews time management work and activities 2L DMD IB exams ISEE MD/PhD programs Sentence Correction adjusting to college algorithms amino acids analysis essay athletics business skills careers cold emails data science dental school finance first generation student functions graphing information sessions international students internships logic networking poetry resume revising science social sciences software engineering tech industry trigonometry writer's block 3L AAMC Academic Interest EMT FlexMed Fourier Series Greek Health Professional Shortage Area Italian Lagrange multipliers London MD vs PhD MMI Montessori National Health Service Corps Pythagorean Theorem Python Shakespeare Step 2 TMDSAS Taylor Series Truss Analysis Zoom acids and bases active learning architecture argumentative writing art art and design schools art portfolios bacteriology bibliographies biomedicine brain teaser campus visits cantonese capacitors capital markets central limit theorem centrifugal force chemical engineering chess chromatography class participation climate change clinical experience community service constitutional law consulting cover letters curriculum dementia demonstrated interest dimensional analysis distance learning econometrics electric engineering electricity and magnetism escape velocity evolution executive function freewriting genomics harmonics health policy history of medicine history of science hybrid vehicles hydrophobic effect ideal gas law immunology induction infinite institutional actions integrated reasoning intermolecular forces intern investing investment banking lab reports linear maps mandarin chinese matrices mba medical physics meiosis microeconomics mitosis mnemonics music music theory nervous system neurology neuroscience object-oriented programming office hours operating systems

Related Content