Author Archives: hangtime
Newton's Laws of Motion
This video covers those magical three Newton's Laws: Newton's First Law, Newton's Second Law, and Newton's Third Law. He was very creative with the names, that Newton guy.
This chapter covers those magical three Newton's Laws: Newton's First Law, Newton's Second Law, and Newton's Third Law. He was very creative with the names, that Newton guy.
Units of Force (Newtons)
These days, Newtons are the only unit of force that any physics profs seem to use. But that's actually good for you, because even though they're funky when you first see them, by the end of this video you'll see that as long as you always use kg and m/s2 in all your calculations, Newtons are easy!
Contact Forces vs Field Forces
This video quickly explains the difference between contact forces and field forces, and gives you a few examples of each.
Net Force & Equilibrium
This video explains what "net force" is, at least for physics (not sure about fishing). Bad news: it's a vector sum, so you'll have to use X & Y components! But you've been to that rodeo before, like in projectile problems, so should be plug and chug at this point. Also defined: equilibrium, and how a car can be at equilibrium while going 50 mph down the highway.
Mass vs Weight
This quick video explains the difference between mass and weight, and gives you a couple of examples that will come in handy if you're answering a short answer question about it!
Common Forces You Should Know
This video briefly explains and gives you the basic formulas for a bunch of forces you'll be seeing a ton in the forces section of physics: Tension, Springs (Hooke's Law), Weight (gravity), Normal Force, and Friction. The most useful of those is probably normal force, since that's the one with the least helpful name.
This chapter covers all of the basic vocab and concepts that you could need for multiple choice and short answer questions about forces. Lots of vocab and intro to forces you should know: Tension, Springs (Hooke's Law), Weight (gravity), Normal Force, and Friction. Also covered are the difference between mass and weight, and contact and field forces.
Linear Velocity In Circular Motion
In centripetal acceleration problems, sometimes they just give you velocity (the "v" in a=v2/r). However, often they give you that speed in another form such as RPM (revolutions per minute), Hertz (Hz, revolutions per second), or period of orbit (either orbits per year or years per orbit). This video is about how to convert those funky units into the linear velocity you want (m/s). For more, check out our unit conversion & dimensional analysis videos.
Centripetal Force vs Centripetal Acceleration
Later in physics, we'll have a bunch of videos on advanced centripetal force problems. This video is only meant to introduce the topic in the way you might see it in the kinematics section of your book, which is where books usually first introduce the centripetal force formula (a=mv2/r). Examples include: how fast you can swing a yo-yo before its string breaks, and the lateral force created by a car going around a turn.
Centripetal Acceleration & Satellite Orbit Problems
This video covers a variety of centripetal acceleration problems. We start with the basics of the centripetal acceleration formula (a=v2/r). Then we get into common examples: we calculate the speed a roller coaster should go over a 15-m radius hill such that it barely doesn't leave the tracks, and we calculate the velocity a satellite must have to maintain a circular orbit. Fun fact: both examples require setting centripetal acceleration equal to gravitational acceleration(g)!
Tangential vs Radial Acceleration
While most physics classes at least mention this topic, most don't dwell on it too much. The main thing is that you'll want to know what the terms "radial" and "tangential" mean, because those labels are often used in a wide variety of word problems, from rotating bodies to forces to torques to statics.
Centripetal vs Centrifugal (Fictitious) Forces
This video explains the basics of the centripetal acceleration formula (a=v2/r), then it gets into explaining the difference between centripetal and centrifugal forces, also explaining why the latter are referred to as "fictional forces". Cool example: when you're in a car going around a turn, squishing the person next to you, are you squishing him, or is he squishing you?
These videos cover the most basic circular motion problems, the ones you get BEFORE your class does forces, Newton's Laws (F=ma), etc. In these videos we're just covering basic centripetal (and centrifugal) acceleration problems, including situations like satellites orbiting a planet, or a roller coaster going over the top of a hill. A later chapter of videos in the Forces section will cover advanced circular motion and F=ma problems.
Quadratic Formula on Calculator
This is a quick tutorial on how to do the quadratic formula on your calculator if you don't have one of those programs that does it for you. The main thing is being organized with your parentheses, and there's also that great 2nd-Enter trick so that you don't have to re-type everything for the second part of the "plus or minus" at the center of the quadratic formula.
Ski Jump Problems
You may not have noticed, but all the projectile problems up to now have dealt with level surfaces: whether the object was being dropped from an airplane or shot from a cannon, it always seems to be landing on a level surface. This video tells you what to do with a ski jump or other situation where the landing surface is a slope or other shape that can be defined by a function of X and Y.
That Problem Where Something Falls From Tree At Same Time Gun Fired
This video covers a problem that's very common in physics lectures: your prof might do it as an in-class demo, or if you're really lucky you might get to do it in lab! A dart is fired at the same time the target is dropped, yet the dart magically hits the target on the way to the floor. Awesome.
Projectile Aimed At A Target
This video covers a problem where a gun or arrow is aimed at a target, but gravity causes the projectile to miss low. The second, trickier half of the problem is when they ask you what angle to correct the aim by to compensate for gravity. Sounds reasonable, but it seems like it requires a few little tricks that most students aren't aware of, so I do my best to explain how I'd approach this one.
Will This Projectile Clear The Obstacle?
The problems in this video are things like: If a football is kicked at a certain speed and angle from 65 meters away, will the ball clear the horizontal bar that's 3m off the ground? The basic idea is that instead of asking you how far a projectile will go, they give you a distance and ask if the projectile will be high enough to clear it. Another popular topic for this type of problem: whether a baseball will be a home run.