Friendly Physics

So what is a force?A force is really just a push or a pull on an object. It occurs when two objects interact with each other. Forces can be contact forces, meaning that the objects have to actually touch. Or they can be at a distance, think along the lines of magnets or gravity. A force is still present but the objects are at a distance. It helps most to think about forces in terms of balance. You might hear the terms balanced or unbalanced forces. Just as with velocity, we split forces into dimensions. So we talk about vertical forces and horizontal forces. Forces that act in the vertical dimension and forces that act in the horizontal dimension. When balanced forces act on an object, that object does not move. Imagine tug of war where both teams are pulling completely equally. The force to the left is the same as the force to the right. They cancel each other out. They’re balanced. Unbalanced forces are forces that act on an object unequally. Imagine one tug of war team pulling with 70 N of force and the other team pulling with 40 N of force. They are unequal. They are unbalanced forces. The team pulling with more force will move the other team.

However, we don’t always just move objects at a parallel to the ground. More often than not, we move them at an angle. Think about your field goal kickers on a football field or a missile being launched. These objects move up, peak and then come down.We say that they follow a trajectory. They exhibit parabolic motion. The objects peak and then they fall. They are projectiles.There are many important things about this motion. First, lets focus on that angled launch. Remember how last time we had to pay careful attention to the phrasing of the problem? Was the initial velocity horizontal or vertical?Last week we talked about initial horizontal velocity. Objects launched parallel to the ground. But this week the launch is at an angle and so the velocity can be split into horizontal and vertical components.This is where geometry and trigonometry comes into play. Let’s imagine that a football is kicked at a 30 degree angle from the ground with an initial velocity of 28 m/s.The initial velocity is 28 m/s at a 30 degree angle. Velocity is a vector. Direction matters and therefore we are able to split the velocity into horizontal and vertical components.

The past few weeks we have moved on from talking about objects moving horizontally, back and forth, and started to talk about objects that move vertically, up and downWe started off by thinking about objects that fall, like an apple from a tree or a book off a shelf. Then we started to discuss objects that launch upward, like rocketsAnd today we are going to connect the two Because what goes up … must come downWhen an object is launched, it goes up and up and up, until it STOPSAnd that is where we stopped in the last episode as wellHowever, in reality we all know that when an object is launched, it goes up and up and up and then it stops and THEN it falls right back down to earthNaturally, I want to ask some questions about how that object falls.

Last week we listened to the start of a new idea. We expanded on motion and are now talking about up and down → vertical motion.We spent a lot of time getting accustomed to objects moving - where they are, how fast they move, what direction that movement is inAnd now we’re applying it to objects that are withstanding the force of gravity.Last week I gave you two equations → the first one was simple. It says v is equal to Vo (initial velocity) + a times t. (acceleration times time)The other formula was a little more complicated.The formula says position equals initial position + initial velocity times time plus ½ acceleration times time squaredY = Yo + vo t + ½ a t^2To truly use these formulas and to do so successfully, is to understand vertical motion.Vertical motion is an object moving up or down. I want you to imagine an apple falling from a tree when we are talking about an object falling down. I want you to imagine one of those stomp rockets where you set a little foam rocket on a launcher, attached to a pump that you step on and then the rocket goes up when you stomp. Imagine that rocket when we are talking about an object launching up.

We are wrapping up one dimensional motion today with all of the key ideas covered. We’ve talked about distance and displacement, speed and velocity and last week we talked about acceleration as the rate of change of the velocity over time.We talked about how positive acceleration means the velocity is increasing, the object is speeding up, and negative acceleration means the velocity is decreasing, the object is slowing down.And then, I left you with a few challenge questions... I asked you to imagine a runner on a track, starting at the starting line and picking up speed at a constant acceleration. That meant that the runner had a positive velocity → because they were moving away from their initial position and a positive acceleration because their velocity was increasing.Often times, we will see position, velocity and acceleration tracked graphically in physics.If you can master the skill of graphing, it makes understanding these relationships even easier. Feel free to pull up a graph right now if it will be easier for you to visualize this.Time will always be on the x axis side to side and the y axis up and down will either be position, velocity or acceleration.

How do we discuss HOW FAST an object moves?Let’s start with speed:SPEED is the rate at which an object covers ground.If you’re a math head like me:SPEED is distance divided by time , the distance an object travels in a unit of time.If you are driving 70 mph → you can cover 70 miles in one hour . . . if you are going at a constant speed.

Let's start off by discussing the idea of movement.What is movement?How can someone move?Do we care about direction?Do we care how fast someone is going?If we really want to start off with the basics, then lets answer this question today:How much does an object move?We have 2 different ways to answer this question and that is where distance vs displacement comes into play.