Car Crashes

This week's physics class, as far as I'm concerned, was the most fun yet.  Even my friend said that she now officially loves physics because of this class.  I mean, we did get to "blow things up."

My teacher said that this week, instead of having another discussion on motion before the Thanksgiving break (even though he does agree that we need more), he decided to let us "make" action movies. Apparently he loves them, so he came up with three different scenarios for us to chose from.

The Rules

My teacher decided on giving us a set of rules so that this wouldn't be too easy.  They are as follows:

1. You only get one shot at it, and if you screw up, "you'll never work in this town again!"
2. You cannot test it out beforehand.
3. You must follow your scenario exactly, meaning that, if it gives you measurements, you must use them.
4. Your two cars will be at different speeds.
5. You cannot run both cars at the same time.  Only one can run.  Otherwise, you will be disqualified.
6. If you make the two cars crash and you follow the scenario, you will "have your people call his people."

Our Scenario

My group and I decided to chose scenario number 1.  In this scenario, we had to have two cars come at each other from two different directions.  They MUST be 2 meters away from the crash point, but we get to decide at what time we should start each car.

Of course, one car was slower and one car was faster.  To make it a bit more comical, we decided to name the slower car Grandma and the faster car something about speed.  I can't remember the real name we came up for him, except for the fact that I called him Speedy McSpeedson.

Our Process

To find out how fast each of the cars went, we decided to measure how much time it took for each car to travel 1 meter.  We then doubled it to see how much time it took for 2 meters.  For each car, we actually recorded the time 5 different times to make it more accurate, and then we found the average.

• Grandma: 1 meter= 5.6 seconds, 2 meters= 11.2 seconds
• Speedy McSpeedson: 1 meters= 4.26 seconds, 2 meters= 8.52 seconds

From this data, you can obviously tell that Speedy was faster than Grandma.  However, we actually got stumped on what to do next. Eventually, we figured out that all you had to do was subtract the two times to find out when to release the second car.  We did 11.2- 8.52 and found that the answer was 2.7 seconds, meaning that we needed to release Speedy McSpeedson 2.7 seconds after we released Grandma.

In the End...

In the end, we ended up succeeding and causing the cars to crash.  It felt good to have gotten it right.  I'm very happy that I got to work with my group.  They all did a great job trying to figure out the answer, and everyone in the class, including myself, had a great time.  Personally, I would like to do another activity like this one again.

Another Worksheet... Darn

Hello everyone out there listening, or I guess reading, if you want to get technical.  This week, just like the last one, I had to miss class.  You can blame my orthodontist for this one, but of course, missing class meant missing another discussion, and I really don't like missing discussions.  I mean, those things contain some valuable information which now, because of my appointment, I will never know.  Really, all I took out of this week was a fairly easy fiesta (quiz) and a worksheet.

Fiesta

You all know how it is.  When you think something is easy, you usually end up doing horrible, especially in a class like math.  However, I seemed to understand the fiesta.  After all, it was on Position vs. Time graphs which are easier for me to comprehend anyway, so overall I think I did pretty good.  I've got my fingers crossed.

Worksheet

The worksheet was called Constant Velocity Model Worksheet 4: Velocity vs. Time Graphs and Displacement.  We were told to do the worksheet with our tables and discuss any questions we had. Again, like the fiesta, I didn't find this to be too hard, and I found it very helpful to work and discuss in a group.

Basically, the worksheet went through making motion maps, writing written descriptions of the motion of objects, making Position vs. Time graphs, making Velocity vs. Time graphs, writing mathematical expressions for motion, and determining displacement.  However, there were three other things which still kind of have me confused; the area under the curve, average velocity, and average speed.

The Area Under the Curve

The only reason I understood this part of the worksheet was because I had actually watched a video on my own about it.  The area under the curve is basically the area of the "squares," I guess, on a Velocity vs. Time graph.  You would basically do length times width or base times height or side times side (whichever you prefer) to get the area of each little rectangle, and then you would add them all together to find the total area under the curve.  Supposedly, this comes out to the displacement of the object, so this could actually be quite a handy way to find it.

The graph above is actually the Velocity vs. Time graph from the worksheet.  If you notice, there are three rectangles, and if you were to find the area of those and add them, then you would find the total displacement.

If you were wondering what you do for the "non-rectangle" parts, you basically do nothing. Technically, you would find the area of them too, but since it isn't a rectangle, it only has one dimension, so its area is technically 0.  Basically, there is no need to find it because it is always 0.

Average Velocity

For this one, I must thank my group for helping me figure it out.  To find average velocity, you first need to know what velocity is.

Velocity is basically speed with direction included.  This hints that velocity can be negative.  If you used the graph above, and you were asked to find the average velocity form t=4 to t=8, you could do so easily.

All you do is take the firs velocity at t=4, which happens to be 3 meters/second, and add the velocity at t=8 which is -5 meters/second. So, 3+(-5)= -2 meters/second.

You would then divide by the amount of time passing to get the average.  This comes out to be 4 seconds, so you would do -2/4 which is equal to-1/2 meters/second.

Average Speed

Again, I must thank my group for helping me figure this out.  However, we still aren't 100% positive on this one, so I may be wrong in what I am saying.  To find average speed, you need to know what speed is.

Speed is distance divided by time.  There is no mention of direction in the definition, so we know that speed cannot be negative. 

If you were asked to find the average speed from t=4 to t=8, you would take the two velocities mentioned before and make them positive.  You would get 3+5=8 meters/second, and you would then divide by 4 to get 2 meters/second.

Reflection

Again, I am not positive on the average speed portion of this worksheet, but I am fairly certain about the other parts.  Truthfully, I wish that I hadn't missed two days of class.  It really makes me feel behind, but I guess I have to embrace the confusion like they always say.  I hope that I can get back on track next class. Although, I know for sure that all I can do is try my best.

Lists of Motion Info

This week, sadly, I was only able to get one class worth of information.  Today in fact, was supposed to be my second day for physics this week, but of course I had to be absent.  I really hope that I didn't miss too much, and that our fiesta (test, quiz thing) wasn't too hard.

Anyway, this week, we continued to focus on motion.  However, we definitely got more in-depth on different parts, especially this new term called displacement.

Displacement is the change in position, but it is NOT I repeat NOT distance, however close the two words may sound.  I mean really, why start them both with the letter D?  That just makes things more confusing for everyone.  To explain, I should probably review the words that could possibly confuse me more and show how they are different.

The Differences

1. Distance

• Distance is the total amount traveled.  For example, if you walk 9 steps to the right, 3 steps back, and 1 step left, your distance is equal to 13 steps.
• Distance compares two (or more) locations.  For example, if you travel from point A to point B, your distance is the length between the two.

2. Position

• Position is the point you are at at one point in time.
• To find your position, you use your reference point.
• There is only one way you can get to the position that someone else is in right now.
• Position deals with direction.
• Position can be negative or positive depending on the direction relative to the reference point.
• Position is a single point, like Point A. 
• To sum it up, position is the distance from a reference point (with direction) at one point in time.

3. Displacement

• Displacement is the change in position.
• Displacement has direction associated with it.
• It can be negative or positive.
• Displacement is where you end up relative to your starting point.  For example, if you go on a long journey, the only thing that matters for displacement is where you end up and how far that end point is from where you started.
• In another sense, if you start from point A, then walk to point B, then walk to point C, displacement is only how far you are from point A to point C.
• Displacement uses the starting point, not the reference point.
• To sum it up, displacement is the change in position relative to the starting point, not the reference point.

Putting Things Together

So now that you know that these three terms are obviously different, let's relate them to something else... like... Speed and Velocity!

As a class, we deduced that displacement seems to go more with velocity, while distance goes with speed.

Speed= Distance/time

Velocity= speed with direction= Distance/time with direction= Displacement/time

Reflection

I realize that this blog is kind of a mess, but that's a little like how I feel right now.  Missing today definitely didn't help, but it couldn't be helped.  I'm still pretty confused, although a little less so, and I hope that my understanding will increase next week.  However, I will have to take my fiesta next week, and I am a little worried.  I guess all I can do is try.

All Parts of Motion

Position vs. Time graphs, Velocity vs. Time graphs, and Motion Maps.  Anyone know what those are? Anyone?  Well I'm not sure I know either.

This week, we learned about the three things mentioned above, but of course, my mind jumped from certainty to confusion and back again, as I tried to figure out how they worked.  I felt so dumb, especially because I had gone through all of this last year, with the exception of motion maps.  I started off only remembering the names.  Then, there was a flash of light and I instantly remembered what they were, but then I forgot how to draw them.  Then, there was yet another flash of light as I remembered, but now I'm not positive I'm right.

My class seems to be very confused, and that is not boosting my confidence.  Usually, I have a pretty good grasp on what's going on, and I still kinda do.  It's just that we haven't really figured out exactly what they are, and of course our teacher won't tell us.  We have to learn it for ourselves, and I guess that does make sense to some degree.

My First Understandings

This week, we did a lab that dealt with Position vs. Time graphs and Velocity vs. Time graphs.  We were given one of them, and we had to figure out the other.  To do so, we were given a motion sensor and a computer.  We had to try to mimic the graph given, and then draw the other, so if we were given a Position vs. Time graph, we had to do a "walk" in front of the sensor to try to make that graph.  At the same time, the computer would make the other graph, in this case a Velocity vs. Time graph, and we would draw it on our packet.  Then, we would put our "walk" into words, and then draw a Motion Map.

Off of this lab, my understandings were:

• I have no idea how to do a motion map.
• Position vs. Time graphs are easier to do than Velocity vs. Time graphs.
• Your motion sensor is the reference point. (definition in my other post http://ittakesphysics.blogspot.com/2013/10/movin-around.html )
• When you walk towards the motion sensor (reference point), your Position vs. Time graph goes down towards the x-axis, and when you walk away, your Position vs. Time graph goes away from the x-axis.
• If you go at a constant speed, your slope for your Position vs. Time graph is constant.
• If the line is flat on a Position vs. Time graph, your position is constant.
• I seem to only understand Position vs. Time graphs.
• I think I did the lab wrong...

Worksheet Understandings

Then my teacher decided to give us a worksheet called Constant Velocity Particle Model Worksheet 2: Motion Maps and Velocity vs. Time Graphs. Yep, it's a mouthful, but it helped me out greatly.

Off this worksheet, I found out that:

• When an object moves in a negative direction, the velocity is shown as a negative velocity on a Velocity vs. Time graph and when moving in a positive direction, it's the opposite.
• When an object isn't moving, the velocity is 0.
• When an object moves at a steady speed, the velocity is a constant, straight line.
• If the object starts off in one direction at a constant speed and then changes its direction, but still goes at the same constant speed, the graph would look like this:
  
  
• If the object is going the same speed, but in a different direction, the line needs to be at the same number, but negative.
• If the object changes speed, you draw a line straight down because it is changing its velocity instantly.
• This website helped: http://www.physicsclassroom.com/class/1dkin/u1l4b.cfm

Motion Map Understanding

Our teacher then emailed us a reading on motion maps to help us do them on the worksheet. It's http://daisleyphysics.com/worksheets/mmap.pdf 

I learned that:

• Motion maps look like this:

• If an object moves at a constant speed, the arrows have to be the same length.
• To draw one, you must put a point for each time marked.
• The slower the speed, the shorter the arrow, and the faster the speed, the longer the arrow.
• If an object doesn't move, or stays in the same position, you use dots for each amount of time, and since the object doesn't move, the dots stack.
• From the picture above, each notch on the line is a meter.  For the first arrow, it starts at 0 meters.
• If an object turns around, the arrows do too, and they can go over each other because they head back to 0 meters.
• If an object moves in a positive direction, the arrows go to the right, and if the object moves in a negative direction, the arrows go to the left.
• I am still a little confused.

Reflection

This week, I was more confused than I have ever been so far in the year.  However, we still need to have a real, in-depth discussion on it, and I think that will help.  I am doing good in my groups as well, and I am still participating and helping out.  I also feel like I only talk when I need to, at least that's what I try to do.  I am trying not to talk too much, and I am trying not to talk too little.  I guess it's all about making sure I understand, and that is why I have decided to ask questions to clarify certain things that we talk about.

Motion Detectors, Cyclists, and Motion Maps

Hey everyone!  Don't worry, I'm still here, but this week, I've come to the realization that my blogs are long... VERY long.  I've realized that you guys probably don't want to read all that lengthy garble, so I'm going to try to cut it down, just for you.  You had better feel special...

Anyway, this week in class, we discussed motion... again.

I have this odd feeling that the motion section is going to last for a long while, seeing as how confused the class is, as well as myself at certain points in time.

For most of the week, we had a class discussion on this worksheet we did called "Unit 2 Worksheet 1".  I know guys, I love the name just as much as you do.

Question 1 

Anyway, for this worksheet, we were asked multiple questions about this graph for question 1:

If you didn't read the little blip above the graph, this graph is specifically a position vs. time graph and it has to do with 2 cyclists, Cyclist A and Cyclist B.  Position is the y-axis (in meters) and time is the x-axis (in seconds).  In our class discussion, we found:

• The cyclists do not start at the same point.  Cyclist B starts before cyclist A because it is farther up the y-axis.
• The reference point is the origin which is where Cyclist A started.
• When the time is 7 seconds, Cyclist A is ahead because it is above Cyclist B, so it is in a position which is farther away.
• When the time is 3 seconds, cyclist A is travelling faster because its slope is steeper.  Although, this is what I believe.  There is some controversy in my class on whether or not the slope is the speed.
• Their velocities aren't equal at any time.  Again, this is what I believe because it is still being debated.  To me, their slopes are never the same, so their velocities aren't.
• At the intersection of the two lines, they are at the same position at the same time.  However, they are not at the same speed or velocity.
• The biker's speeds are constant because it is a straight line.  My belief again.
• My theory: Velocity=Distance/Time and since position is measured in distance (y-axis) and time is the x-axis, it only makes sense that the slope is velocity.
• You don't travel a position, you travel a distance, so a certain point is a position, while the line is made up of tons of different positions.
• Position= Speed times Time + Starting Position or P=Speed times t + Po

Question 2

For question 2, we used the original graph and another:

We were asked basically the same questions as in question 1.  As a class, we found:

• Compared to the old Cyclist A, the new Cyclist A is going in the opposite direction.  It is going towards the x-axis or the starting point, instead of heading away from it.
• Compared to the old Cyclist B, the new Cyclist B is going the exact same speed.
• Cyclist A has the greater speed due to steeper slope.  Again, very controversial.
• At the intersection, they are at the same position at the same time.
• During the first 5 seconds, neither cyclist traveled farther.  At exactly 5 seconds, both cyclists end up at the same position.  The speed at which they got there doesn't make a difference.  They still ended up in the same place.

New Lab

We also started a new lab with motion sensors and motion maps.  However, since we haven't finished it yet, I will save it for  my next blog.  Also, does anyone know what a motion map is?

Reflection

This week, I have decided that my new goal is to speak only when I am absolutely necessary, and when I have a question of course.  If there is ever a lag in the conversation, I will try to come up with something to say or ask to keep the conversation going, as well as to benefit others.  Also, as mentioned before, my blogs are very long and "thorough" as my teacher would say.  I did try to cut it down, but I'm not sure it worked.  I just have so much to say.