UNIT 4: Blog Reflection

Unit four is based off of Hewitt's Conceptual Physics textbook: Chapter 8.

First, we covered distance and speed involved with circular motion.

Linear speed is the same thing as just saying speed. Speed is the distance traveled over a unit of time. When you travel a greater distance it means you are increasing your speed as well. Remember it like this: greater distance means greater speed.
Tangential Speed is the linear speed of an object moving along a circular path. This could be for example, a car or a merry go round. The direction of the object's motion is tangent to the circumference of the circle.
Then we learned about rotational speed also called angular speed. This is the calculation of the number of rotations an object does over a unit of time. The unit used in rotational speed is RPM (rotations per minute). When you have a greater RPM, it is faster in speed.

The sentence before this one, proves that tangential speed is directly proportional to rotational speed.

Furthermore, there are two different types of relationships between tangential and rotational motion.

1. Same tangential, different rotational
• ie: Gears
• The rotational speeds are different because of the size of each gear and the tangential speeds are the same because they are traveling along the same number of knots because they are all connected and they are covering the same distance in the same amount of time.

Different Size Gears//all connected

    2. Same rotational speed, different tangential speed

• ie: whips//train wheel design
• The rotational speeds are the same but the tangential speeds are different because of the distance from the axis of rotation.

Secondly in this unit we covered Rotational Inertia//Conservation of Angular Momentum

Once again, we know that inertia is the property of an object to resist changes in motion. Inertia is measured in mass.

But moving forward, we have to know about rotational inertia. Rotational inertia depends on the distribution of mass and also the property of an object to resist changes in the spin. If there is more rotational inertia it is harder to spin, if there is less, it is easier to spin. 

In class, we did a demo with rulers and lead weights. On one ruler, we attached two lead weights to each end and on the other ruler we attached two lead wights really close to the center of the ruler. The ruler with the weights closer was much easier to spin therefore it has a small rotational inertia. The one with the weights on each end was much more difficult to spin, so it has a larger rotational inertia. 

The main question with rotational inertia is: How far is it from the axis of rotation?

Arms spread out: Far from axis
Arms closer together: Close to axis

Along with this lesson we learned about the conservation of angular momentum. Previously we learned about regular momentum and the formula for that was momentum before=momentum after. In this lesson, it is the same! Angular momentum before=angular momentum after.

The formula for angular momentum is: (rotational inertia)(rotational velocity)=(r.i)(r.v)

When there is bigger rotational inertia, the rotational velocity is smaller and vice versa.

Another thing we learned is about torque, not to be confused with the famous dance move twerk.
Torque is a force that causes rotation. Torque involves two different thing: force and a lever arm. This is how we get the formula for torque. Torque=force*lever arm

Torque on a balance. Where it says torque arm, replace with lever

Something that is super important about this concept is that the force and lever arm must be perpendicular; no exceptions.
The lever is basically the distance from the axis of rotation.
Base of support is the idea that if it wont fall there is no torque. In order for this to happen, we want a large base of support.

A concept following torque was center of gravity//mass
Center of gravity is when gravity acts on the center of mass. Gravity is also a force.
Center of mass is the idea that all objects have an average position of all their mass. This is what causes us to rotate and fall down.

The last lesson of this unit included centripetal//centrifugal force. In order to talk about this lesson we must review what inertia is again. To restate, it is the property of an object to resist changes in motion. Inertia is measured in mass.
Centripetal force is a center seeking force which is the only force acting on you.

Centrifugal force is a center-fleeing force which is fictional. it is not an actual force. What it really is, is a feeling that you are being pushed outward. Look at the image below to distinguish the two, but remember centrifugal is fictional so it doesn't really exist.

Examples of centripetal forces are: satellites that remain close to the Earth, washing machine holes, roller coasters, race cars on the race track etc.

The Difficulty

The only thing that was difficult about this unit is being forced to think that in the torque equation, we have to remember that there is a lever arm and not only the force. Also in the beginning the train question was pretty difficult to understand and to be honest, I just learned it today!

I overcame these difficulties by going to Ms. Lawrence during my free period and asking questions and telling her what I knew, which was super helpful. I think all I needed was some clarification. 

Effort, Learning, Problem Solving

Effort: in class, I feel like I participate enough to understand the concepts that we are learning and to possibly clarify for my peers as well. Homework wise, I stay on top of my work and have not missed one assignment since the semester started. In the one lab we've done so far, I was the one who worked past school hours in order to figure out the answer for my group. I've completed ever blog post and commented on Hunter's blog every time. 

Learning: I used to be kind of bad at verbalizing what I was thinking and the concepts we learned in physics. By going to Ms. Lawrence's class, I've learned to speak the lessons we've learned and also translate them to the paper. Thus, my self confidence has risen a lot because I feel like now I know what I'm saying and I'm not only putting it on the paper. My patience level definitely went up as well because I know that when I don't understand a concept, I will be able to understand in a matter of 24 hours by seeing Ms. Lawrence outside of class. 

Goals

My goal for the next unit is to keep doing the things I've been doing so far if they help me do well on the test that is coming up. 

Connections

Rotational inertia relates to my everyday life because I used to be a dancer and now I understand why my dance teacher would tell us to tuck our arms in in order to go faster. 

Centrifugal force relates to every day life when I ride roller-coasters at amusements parks during the summer..i'll be thinking about physics next time I ride one. 

Podcast:

Here is our podcast! Enjoy!