Mass of Meter Stick Lab Reflection

In the demo's, Ella and I drew various examples of the meter stick, its lever arms, its attached weights (forces), and in result, its clockwise and counterclockwise torques. During the planning phase, we were sure that we'd use the equation w=mg because we want to find the mass of the meter stick, not the weight. The obvious first step was to find its center of gravity, and where it would balance equally on the table and in the air.
When we began our lab, we immediately wanted to find the center of gravity with the 100g weight attached to one end. The numerical value for the center of gravity was 21.6 centimeters. Next, we used our knowledge that (f)(lever arm)=(f)(lever arm). Before this step, I understood what that meant, but I had an "aha" moment that the force and lever arm from each side of the center of gravity multiply to equal the same equation from the other side. This was huge for me! Our goal for this step was to find the weight of the whole stick, and that equaled 6.3N. Using the formula, w=mg, we found that the predicted mass of the meter stick was 130g.
Next we massed the meter stick on the scale and found that its actual mass was 119g. Here is a photo explaining our work and how we used formulas to solve for the mass.

Unit 4 Resource Post (Rotation)

I found this image really helpful because it explains what happens when an ice skater's arms and legs are extended and when they are tucked. In the image on the left, the skater's limbs are extended therefore creating a large rotational inertia because it is harder to spin. It is harder to spin because her mass is farther from the axis of rotation.
In the image on the right, the skater's arms and legs are tucked creating a lower rotational inertia due to her mass being centrally located near her axis of rotation. Therefore, her rotational velocity is large and she spins much faster.



In this yoga pose, the woman has a low center of gravity and a large base so that she won't fall over. Because of her wide base of support, she is able to maintain her center of gravity and stay balanced.

Unit 3 Blogpost

Throughout this unit, most things we studied revolved around Newton's Third Law which states that, "Every action has an equal and opposite reaction." At first, this was hard to comprehend because in a car crash, one car is impacted more than the other, but how is that possible if they have equal and opposite reactions to each other? After learning more about what factors in to these problems, I learned that the acceleration of the respective cars has a huge impact on the result of the crash. If a truck and a sports car collided, the truck would have a bigger force not because it was going "faster" but because its acceleration was higher because of its greater mass.

A tug of war game is surprisingly similar to the car crash in that the weight of each team is irrelevant because the forces are equal and opposite. However, the amount of friction that the teams put in the floor determines the winner.
An easy example to help understand how forces work in perpendicular directions is which way a boat will go in a river. If the current is going downstream, and the boat is traveling to the right, the boat will go southeast in order to get to shore. A connection I made was using the special right triangles from Geometry last year in order to find the third velocity value. If two were labeled 3 and 4, I could assume that the hypotenuse would be 5, and that was comforting to have that knowledge up my sleeve.
My favorite topic we studied during Unit 3 was what forces happen in order for ocean tides on earth to do what they do. There are two types of tides that occur on earth, called Spring and Neap tides. The difference between the two is the amount of force the moon is pulling on earth with, and therefore how far the moon is from the earth. I know this because F~m and F~1/d. These formulas mean that Force and mass are directly proportional while Force and distance are inversely proportional. Spring tides occur when the sun, moon, and earth are perfectly lined up, while neap tides occur when the sun and earth are lined up, but the moon is off to the right or left of the earth. The results of these two tides are very different. Because F~1/d, the closer the moon is to earth, the greater force there will be. Spring tides create extreme high and low tides and neap tides are less extreme and normal. This is because when Spring tides occur, there are two strong forces on the earth: the sun and the moon. Although the sun does have a larger force on the earth because of its mass, some of that is diluted because of its far proximity to earth. That is why the moon has a greater affect on earth's tides. Tidal bulges occur when the moon is pulling on that part of the earth thus creating high tides. High tides occur simultaneously on opposite sides of the earth because the tide changes every six hours (from low to high). It takes twelve hours for a beach to have a high tide and then another one.

One of the biggest topics we learned about was momentum. Momentum is the measure of inertia in motion, and the symbol for momentum is p. The formula to find the momentum of an object is p=mv. If the momentum changes, then the mass and velocity increase as well. One phrase that was stressed throughout the section was that the momentum before a collision is ALWAYS equal to the momentum after the collision (p total before=p total after). After understanding momentum, we were ready to introduce Impulse (J) which is Force(time interval)=J. Another way to say this is that in relation to momentum, J=△p.
To find the velocity of two objects that recently collided, we would use the formula maVa+mbVb=ma+mb(Vab). By using the masses and velocities of two objects that become one, we can find the velocity of the new object.
After learning about this, we delved into the Law of Conservation of Momentum which states that the p total before = p total after. This law is vital for our understanding of momentum and how we solve for it.

Tide Resource

Each day, there will be four changes of tide. Every six hours, it will change from low to high or high to low. Therefore, every twelve hours, each type of tide will repeat itself. They are distanced in this increment because of the time it takes the moon to orbit the earth.

The difference in force is caused by the position of the moon in accordance with the sun. If the moon is alligned with the sun and earth, then there will be high tides where the moon pulls on the earth as well as the part of the world opposite that. In result, the other two corners of the world that are opposites will experience low tides.

When the moon pulls on a certain part of the world, it creates a tidal bulge which is an excess amount of water which then creates a high tide.

A spring tide occurs when the sun, moon, and earth are all lined up with each other and will result in extremely high tides. This only happens during a full or new moon. In contrast, a neap tide is when the moon is positioned on the right or left of the earth and there is less of a direct pull from the moon. This results in extremely low tides.

Right now (9:34 pm), the tide in Bogue Inlet is rising. The moon at this beach is not full or new, which means that it is currently experiencing a neap tide.

Newton's Third Law Resource

This image supports Newton's Third Law which states that every action has an equal and opposite reaction because both people are pushing equally on each other. This creates the action/reaction pair that explains how the interaction is possible. When the woman pushes on the man, the man is automatically pushing on the woman because of Newton's Third Law.

Unit 2 Summary

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Newton's Second Law:
The definition of Newton's Second Law is a=f/m. This can also be interpreted in that acceleration is directly proportional to force, and inversely proportional to mass. In other words, what ever acceleration does, force also does.
The other aspect of this law is how weight is applicable to an example. The formula commonly used is w=mg. The weight calculated is also the force, so this is a simple way to find the force acting on an object. When you put only a little force on an object, like the child in the swing from the video above, the child does not go very far. However, when you push with more force, the child goes farther.

Free fall:
In free fall, the only force acting on the falling object is the force of gravity, which is 9.8 m/s.
There are two formulas that are used to calculate the how far and how fast aspects of free fall. Respectively, they are d=1/2at^2 and v=at.
If a ball was falling off a building for 5 seconds, it would travel 125m because of the d=1/2at^2 formula. We don't know the distance, but we do know the acceleration (10 m/s^2) and the time, 5 seconds. Similarly, to find the speed of the falling object the formula used would be v=at. Again, we know the acceleration and time, so multiplying those together would yield the velocity.
This example shows the relationship between time and velocity because height and time always determine each other. Therefore, the more time that passes means that the object is falling from a greater height which will yield a faster speed.

These formulas and facts are also applicable to a ball thrown straight up and its descent back down. Here is a picture to help understand the relationship between the two.

Projectile Motion:
In projectile motion, an object is being dropped at an angle. A common example is how far back a plane should be in order for the box being dropped from it to hit a target. The two velocities in this example, vertical and horizontal, and both stay constant. To find how far the box falls, we can use the the height of the plane to determine the time by using d=1/2at^2 and to find the actual velocity, we would use the Pythagorean Theorem. In this example, one side of the triangle represents the horizontal velocity, another the vertical, and the hypotenuse represents the velocity of the object just before it hits the ground. To calculate the horizontal distance the box falls, the d=vt formula would be used.

As this example shows, the object falls according to the vertical and horizontal velocities and also the force of gravity.

Skydiving:

When a person goes skydiving, Newton's Second Law has a bigger connection than you'd think. During a persons fall, the net force and acceleration decrease because they are proportional, while the velocity increases simply because it is falling and therefore gaining speed. The net force and acceleration do increase but only until the person reaches their first terminal velocity. Terminal velocity is when your velocity is constant and your acceleration is 0m/s^2. When you open your parachute, your acceleration and surface area both increase while the velocity decreases. The surface area increase results in the air resistance pushing on the parachute increasing. The two factors that increase air resistance are surface area and speed. 

When a person reaches their second terminal velocity, the net force and acceleration are both at 0, but the velocity is much slower because of the change in surface area.

One thing that made much more sense to me after this unit was the ascent and descent of a ball thrown straight up. I did not know before that there was so much detail in which the ball traveled. I learned about the relationship between time and velocity and how to figure out how long the ball had been in the air. Now when I throw an object straight up, I will know what is really happening.

Here is my groups podcast about Newton's Second Law Lab.

Unit 2 Resource

This image is a really simple illustration of what happens when you throw an object straight up. In class, we did a lot of detailed exercises, but this picture simplifies the motion and shows what is happening in a the "big picture". Sometimes it can be helpful to look at images like this to take a step back and make sure that you understand what is happening outside of a particular problem.
In the image, the initial velocity is 44 m/s however when it reaches the peak of its path, its velocity will be 0 m/s. The force of gravity (g) is always 9.8 m/s squared.