Unit 1 blog post

When you ride in a car and you toss a penny upward, where does the penny land? When trying to find the answer to this concept, I got lucky and guessed that the penny will land right back in your hand. I had made an educated guess, but the reason the penny lands back in your hand is more significant. The penny lands in your hand because of Newton’s First Law: An object at rest tends to stay at rest and an object in motion tends to stay in motion. Now you might wonder how this could possibly relate to the penny. Well, there is another part of Newton’s First Law- the exception. An object at rest tends to stay at rest and an object in motion tends to stay in motion IF no outside force is acting upon it. The car is a closed system, and therefore no outside forces are acting on it. So as the ball pops upward, it continues to move at the same speed as the car.

When you rip the tablecloth from under dishes on a table, why do the dishes stay? Well, we know that the dishes are at rest on the table. According to Newton’s law, objects at rest tend to stay at rest. However, that is not the only reason the dishes stay. The dishes have a greater mass than the cloth, and therefore a greater inertia, so it is easier to move the cloth than the dishes. This relates to another question posed in the classroom. Why, on a hovercraft, is it harder to stop a larger person than a smaller person? When we talked about the dishes’ unwillingness to move, we were referring to their inertia. The more mass an object has the more force you need to move it. Therefore, inertia is the amount of force needed to move or stop an object. Another example of inertia that baffled me most, was the question about a box and a car.  Why would a box inside of a car hit the back when the car accelerates? At first I thought that the force of the car accelerating was what made the box hit the back. I was wrong. The box was at rest, therefore it would want to stay at rest in the same spot. When the car accelerates, the box does what It was happily doing the whole time. The box stays in the same spot and the car moves forward and therefore the box hits the back of the car.

   SEE HOW THE BOX STAYS AT THE SAME POINT????

We also learned about why a hovercraft is in equilibrium, what equilibrium is, and what it takes to have it. Equilibrium is when an object is either in constant motion, or at rest. There can never be friction because the Net force, or the total force, must be zero. Friction is one element that can be called an “outside force”.  Equilibrium is the very essence of Newton’s First law. Equilibrium at rest wants to stay at rest; Equilibrium in motion wants to stay in motion. However, the only thing (that we know of so far) that would get in the way of equilibrium is friction. The “thing” that starts equilibrium is force (a push or pull).

A hovercraft is pushed at the beginning (force) and then can “glide” because there is no friction. The net force at this time is zero and therefore it is at equilibrium. It takes as much force to start an object as it does to stop it. The latter part of a hovercraft’s journey is the stopping part. The force to start the hovercraft is the same amount of newtons used to stop it. Force is measured in newtons.

The math:

Net force is measured in newtons right?

So if I pushed on a cart with 50N to the left and my friend pushes on the cart to the right with 5ON, the net force is zero N because 50 minus 50= zero

More about hovercrafts:

Hover crafts combine Constant Velocity and Acceleration all in one.

When you push the hovercraft it accelerates. The hovercraft then reaches constant velocity because it is in a frictionless environment. At the end when someone has to stop the hovercraft, they push it backwards. What is the hovercraft then doing? Well it is accelerating backwards or otherwise known as deceleration. When you are gliding, the hover craft wants to stay in motion (sound familiar?), and the outside force that breaks the constant velocity is someone stopping it (outside force).

What is Constant Velocity? Constant velocity is when an object is covering the same amount of distance in the same amount of time at each interval. So if I measured a ball rolling on a flat surface each second, the space between each mark would be the same because the ball is moving at constant velocity. Velocity not only refers to the speed of an object, but also its direction. Therefore, velocity is changed by changing speed or changing direction.

VELOCITY IS ALWAYS CONSTANT

ACCELERATION IS NOT ALWAYS CONSTANT.

The equation for constant velocity is velocity = distance/time. Velocity is measured in meters per second. The difference between speed and velocity is that velocity deals with direction.

Acceleration, however, is the change in velocity over time. Acceleration also has a catch. When you roll a ball down a hill, the acceleration acts differently depending on the hill type. The point is: Acceleration can be constant if it speeding up by the same amount every second. If the hill is perfectly straight: the acceleration is constant- meaning it is speeding up by the same amount every second. However, the acceleration decreases and increases depending on the dip of the hill.

If  the dip is like a fat dude’s belly, then the acceleration increases.

If the dip person is like an anorexic persons belly, then the acceleration decreases.

How do we calculate the rate of acceleration? For example, if a car starts at 10 miles and ends at 15 miles after 10 seconds, then we can calculate this by the change in velocity over time.

So: V= change in v/ time.

However, if we wanted to know how fast the object was going, we calculate it with this equation:

Velocity= (acceleration)x time

Or V= at

If you want to know how far, or the distance an object has gone:

Distance= ½(acceleration)x time(squared).

Or D= ½ a x t(squared)

If you are accelerating, then the speed is changing, and therefore you cannot have a constant velocity. If a car is going the same speed around a race track, does it have a constant velocity? No, because the direction is changing! However, if you are driving at a constant speed around the race track, because you are changing direction, you are also accelerating. WHY? This concept confused me until I dissected the equation for acceleration. Acceleration happens every time there is a change in velocity. Just like the equation insists, you can never calculate the acceleration without knowing the time.

A word about friction: the force of friction is always equal but opposite. So if you push a box with 150 N force and the box is at a constant velocity, what is the force of friction?

It is just like the hovercraft problem. There is constant velocity, so the net force must be zero because constant velocity means the box is at equilibrium. If the hovercraft is pushed with 150N, what is the force that is acting on the other side? -150N.  Therefore, even when an object is in constant motion, the friction force must be equal but opposite. However!!!!! If I am pushing a box at 50N to the right and my friend is pushing at 20N to the left, then the net force is 30N not zero.

I Learned about how the graphs depict constant acceleration and constant velocity:

If you want to know where the line will be on a constant velocity graph:  use y=mx+b

You take the equation given to you when you put the data in excel, and then you translate the equation from y=mxtb to distance=slope x time +b

In finding the distance of an acceleration graph, you DO NOT NEED B. But… in the velocity one you do.

If the question asks where the line will be after 5 seconds, you plug the 5 in for x, multiply that by the slope and then add this to “B”.

BUT- this is not the same as FINDING HOW FAST THE MARBLE WAS GOING. If you want to know how fast, you plug in the V=D/T and that is the meters/second. How fast would it be moving after 9 seconds? It would be moving at the same rate that you got from the equation BECAUSE VELOCITY IS CONSTANT.

The graph of constant acceleration is steeper because you are covering more distance per time over time.  We know this because acceleration covers about 160 meters before reaching 5 seconds while the constant acceleration only covers 109 meters at 5 seconds. To calculate the rate at which the line is accelerating: you use A= change in velocity/time

If you want to make a prediction of how far your marble will have traveled after a certain time- you use D= ½ acceleration time (squared)

½ a  represents the “ slope” in y=mxtb

The b is crossed out because you don’t need it.

So basically D= ½ a x time (squared) is really   y=mx

Remembering that applying this equation within a graphing problem is only helping you predict how far it will go, not what the line will look like once its there. That’s what the y=mx+b is for- To see where the line will cross on the graph if you plug in random times for x.  The distance formula is for numbers, the equation excel gives you is for the visual.

If you need to know how fast for after you have calculated the how far it has gone…

REMEMBER- you need to take the number in the slope and multiply it by 2  EX: D= 3.95x T(squared)

Why? 3.95= ½ a …. And in the how fast equation you need the full a…. not just half of it.

Because the number in the distance formula is ONLY HALF THE ACCELERATION

so… V= AxT

v= 2x3.95 x T

remember to include meters/seconds squared because its ACCELERATION.

SO:

Using y=mx+b is only for graph purposes and translation purposes

Velocity=

Use y=mxtb to translate into v=d/t

Acceleration=

Use y=mx+b  to translate (or rather y= mx)

D= ½ a x t(squared)      mx= ½ a x t(squared)       and y= D

 Back to graphing:

In the lab we switched the x and y axis. For the velocity and acceleration graphs we put time in x and distance in y. Therefore the side would show distance and the bottom would show the time. However, when we wanted to SEE the distance change, like literally see it, then you need to switch these.  So distance would go in the x column and time would go on the y column. 

I worked through the lab without very much trouble, but when I was confused I went in for conference period to affirm my answers in the lab. The purpose of the graphs in the lab only made sense to me until tonight because I needed to find the connection between the equations and the graphs. Why did we make the last graph? I was able to see that we needed to make the last graph and switch the colums for a better view of the distance. Somehow I must have missed this in class. When taking the quiz on velocity and acceleration, I found to my surprise that I was able to remember that no matter how long an object has been in constant velocity, it will still be going the same meters per second  (I didn't fall for the trick question basically). 

Collaborating with Cori in the group project allowed me to better understand translating the equations into words and vice versa. However, it was not until making this blog post that I realized the slope intercept form was used simply for a visual aid and that the other equations were only for calculations. Making these slight corrections in my understand has boosted my confidence for tomorrows test. I hope to create more visual aids in the future since I am a visual learner. Going back over the lab and dissecting why each answer was asked helped me realize on a deeper level what each part actually meant. My effort toward being a student has been exemplary. I think I also have grown as a learner and I hope to continue to work hard so that I can enjoy what I am learning. My initiative to get work done in advance has helped with understanding the material since it leaves time to go back and re- absorb it.