Vectors

I feel extremely behind in physics especially with vectors because I've missed 2 classes where we have talked about them. I have only been present for the class where it took 50 minutes to answer one problem. This is definitely something I need to spend extra time on, I've done only 2 problems of this and missed extra class discussion.

I am going to watch a video explaining.

Before video: A vector shows direction in which something moves

https://www.khanacademy.org/science/physics/one-dimensional-motion/displacement-velocity-time/v/introduction-to-vectors-and-scalars

So my idea of a vector was basically correct. So a vector is direction with a size (or magnitude but we haven't used that word in class yet). So if an object moves 15 meters to the right this a vector quantity. I feel like its fair to say, you can group displacement, velocity, and vectors all in the same category. The video also touched on scalar quantities, which I am unsure of if we touched in class. Scalar quantities would be just the distance traveled without the direction. So you can group distance, speed, and scalar quantities together. 

From class the one day I was here we used the pythagoreum theorum and sin/cos/tan to find vectors. I definitely need to do some practice problems from the packet we've done, because I don't have enough experience with this to feel comfortable. I feel like I understand the concept, it's just practicing ways mathematically to figure it out.

Looking at vectors a few weeks down the line<It's easier to grasp. I think what had confused me before was the idea of changing the axis, but this works when trying to solve problems with diagnol vectors. It took me awhile to understand this, I even had to go in for a lunch session, but I think now it is fairly straightforward. 

Beginning of IB Physics SL :)

So far our class has been just reviewing concepts from freshman year, nothing all that new yet. We've covered position, distance, displacement, speed, and velocity. We've mentioned velocity here and there, but really haven't delved into it as much as the other topics mentioned. So i'll just go over a quick run down of things.

So to the left you're looking at a very basic position vs time graph. The topic of comparing position, distance, and displacement came up. So in this example, At 5 seconds:
Position: 50 m
Distance: 50 m
Displacement: 50 m
All of these came out to be the same in this scenario, BUT THIS IS NOT ALWAYS THE CASE!!!!!

So before I dive in deeper, I think it's a good idea to define the terms I've used so far.

Position- Position is the location the object is at. So in the graph above, at 5 seconds the position is at 50m.
Displacement- Displacement is how far the object is relative to the reference point. Direction matters!
Distance- Distance is the amount traveled in total regardless of direction.

So here's a question: What's a scenario where position, displacement, and distance are all different? 

So basically here's an answer. Obviously this isn't the only answer but the general idea applies. Basically to answer this, your starting point and reference point need to differ and at one point you need at least one positive and negative slope on your graph.

So in this graph specifically, the intervals on the y-axis go up by 20, and the x intervals increase by 1. 

I will evaluate the graph at 6 seconds.

Position: 20 m

Displacement: 0 m

Distance: 80 m

Also, since we already have a graph above, we might as well knock two birds out at once and talk about velocity and speed as well.

Velocity: displacement/time

Speed: distance/time

So for the example above

Average velocity: 0/6 = 0 m/s/s

Average speed: 80/6 = 13.3 m/s

Just to tie in acceleration a little, basically the slope of a position vs time graph equals velocity, and then the from the slope of a velocity graph you can get acceleration. 

 The topic of linearizing came up, which confused some. And i'll admit, last year in chemistry we were just handed a worksheet and we were told to linearize without really any discussion on it and I was just lost. But with a little research I knew what it actually meant, and the concept is fairly simple.

 
So basically, this is what helped me the most. If it's still confusing after this, I recommend watching youtube videos that can clearly explain it in a few minutes with examples and whatnot.

We also did a lab which was pretty fun. So basically we were given a boiling flask that was 500 ml, which looked like this:

So basically we measured, and in our flask only the bottom circular portion was 500 ml, and the neck was 50 ml. So our task was to basically record the height at a certain amount of time. So what we did was we did a scale that 1 sec = 1 ml. And since there was 550 ml, theoretically, 25 ml with 22 trials should fill up the entire flask. So basically, we would put in 25 ml of water, which would also represent 25 seconds, and then we would measure the height of the water with the ruler. We ended up having to do 24 cups of 25 ml, due to imprecise measuring (we literally used like 8 different beakers and graduated cylinders because of the time crunch) but this was pretty insignificant because it did not effect what were analyzing. Basically, when the flask is thinner the slope of the position vs time graph would be steeper, and then at the wider parts it would be less steep. What was really cool about this experiment, was that if you turned the flask sideways that's what the velocity vs time graph would look like. I just thought that was really cool and worth sharing about.

FRESHMAN YEAR: a blog i started but apparently never bothered to finish

Dear Blog,
Sorry for neglecting you :) The last post I wrote was back in December when i was still a bit confused on acceleration. Not really that confused anymore, so here's a quick run down of things:

• Speed up, slow down, or change direction
• Slope of velocity vs time graph
• or (this is what I do)...final velocity minus the initial velocity divided time gives you acceleration
• Units/s/s

There is much much much more. That's just what came to mind. Now to current trends: forc. So basically ive learned...(will finish and edit tomorrow) 

FRESHMAN YEAR: Cart on a ramp

All the graphs we've encountered so far have had a constant velocity. 

constant velocity graph

When we set a car on a ramp we have seen that the velocity was no longer constant. The graph looked linear. So it is a constant increase in velocity.

 

So as you see, the two graphs are very different. This graph shows that in every single second the velocity is changing. I really wasn't expecting the graph to look linear because I thought it wasn't possible. Though the two graphs look different, I'm sure you can still calculate the velocity the same way. I think we have to go more in depth with this topic. I remember that Mr. Battaglia said something about acceleration at the end, but i'm not entirely sure what it was. So my question: is the second graph a model for acceleration or is it just simply velocity constantly increasing?

FRESHMAN YEAR: All Things Velocity

Velocity: Speed in a direction (displacement/time)

Speed: distance traveled over time

Position: The location of an object relative to a reference point

Displacement: Change in position

Distance: total amount of travel

Over the past few weeks we've been trying to understand velocity. As you see from above, velocity is speed in a direction. One of the huge questions our class ran into was if it is possible to go from a Position VS Time graph to a Velocity VS Time graph. The answer is yes. Imagine a velocity graph with the velocity of 4 and time increasing by one second. Now imagine a position graph with time increasing by 1 second as well. So, since the velocity is 4, the graph will increase by 4 every second. Also let's say you have position graph, and your position is 12 feet at 3 seconds, if you do the math velocity would be 4. We also discussed you don't have to be at your reference point/position for your velocity to be 0.

  

  In the graph above you see that position increases 5 meters every second. Your velocity would be 5 up until 5 seconds. I found that by dividing position by time. After 5 seconds your velocity would be 0, since there is no change in position. 

Other things we discussed:

New Class Rule: Don't use X or Y to identify the axis' because in the scientific world X represents position and it's just confusing.

Position, displacement, and distance can all be different. If i'm being completely honest, i'm still a bit confused on displacement.

Distance: 200 meters

Position: 0 meters (from reference/starting point)

Displacement: Would it be 0 or 40? Or am I completely wrong and it's something else? Honestly my confusion is coming from not being completely clear on whether we're measuring change in position from the reference point (0) or change in position from the previous time interval (the difference between the change in position from 40 seconds to 50 seconds).

EDIT: Today in class my question was answered. So, that means the displacement would be 0.

FRESHMAN YEAR: How does time affect position?

In our most recent lab, we tested how time affects position. Our group chose to use the black car to do this experiment. We marked every meter with tape down the hall. We chose to use 5 second intervals. So, from the starting point (also reference point), we started the car and once we hit our desired time (5s, 10s, 15s, 20s, or 25s), we stopped it. Then we measured how far from the starting point in meters, and then converted to centimeters.

Our graph was linear, and so was everyone else's, with the exception of one group. This means, as time increases, so does the position of the car. (By the way, the definition of position is the location of an object relative to a reference point, also starting point in this case). Unless speed was changed, our position should have increased the same amount everytime. Our data was a bit off due to human error. We also talked about how this graph should have a 0,0. (0,0 meaning zero seconds in time and zero centimeters in position). Our class decided this, because this is actually measurable, and we know our starting point/reference point is zero.

We did a second experiment that day too. Everything remained the same except our starting point. Our starting point was .5 of a meter behind pur reference point. We started our time at the starting point, but measured position from the the reference point. This graph was also linear. The two experiments were very alike, except the position in the second one ended up closer to the reference point. For our second experiments, all groups had different things they had to change from their first experiments. One of the most interesting ones I saw, was the one where the car had to go in the opposite direction of the original. When put on the same graph, it looks like the first experiment is going in a positive direction, and the second one is going into the negatives. They can actually be flipped around, the first can be negative and the second can be positive, it really doesn't matter. The reason behind putting one into negatives, and one into positive is to show that the car ended up in a different position. If it was a distance graph, and the speed was the same, one line would overlap another.


So basically, thats what we talked about.

FRESHMAN YEAR:Lab Relationships

So far in class I've seen 2 lab whiteboards. I'm not sure, we may have done 3, but I was absent last Friday so I have no idea what we've done. In each of the lab whiteboards we've discussed the relationships we've experimented with.

The first lab I'm going to talk about is lab #6. This was the pendulum lab where we've tested if mass effects the time it takes the pendulum to swing. We discovered there was no relationship between the two. As mass increases nothing happens to the time. The data was not perfect and they did not get the same results each time due to human error. The groups most likely timed wrong. If there was a graph, it would look like a straight horizontal line.

We also did a whiteboard discussion on lab #1. This was the circle lab where we discussed how diameter affects circumference. We came to a consensus and decided if the diameter increases so will the circumference of the circle. Everyone agreed that the graph was linear. For quite awhile, we had a quarrel concerning the y-intercept. We decided that it should be 0, or at least near 0. The equation should look a lot like 3.14


****I got a bit confused and got mixed up on which labs we've discussed and which we've did on our own, just comment if i've missed one...also I'll try to catch up on tuesday and see if what we discussed on Friday. I'll go back and edit my blog if there's new information****

Edits:
Carpet tile lab: main thing we learned that we can't have 0,0 unless you can actually measure the specific point. Also..it was linear so for every .42 grams increase in mass, we get 1 increase in area.

Lever lab: Absent that day, but it should be linear.

We didnt discuss sphere or circle lab #2 in class.