Unit 2 reflection

We started this unit learning about Newton's 2nd Law! Newton's second Law states that acceleration is directly proportional to the Net Force and inversely proportional to mass. The statement is simplified in the equation:


a = Fnet/m

After learning a little bit about Newton's second law we learned the differences between mass and weight. Mass is a measure of inertia and is represented in Kilograms. Mass never changes from one place to another! Weight is a measure of force always represented in Newtons! Weight does change from one place to another because w = mg and the gravitational force is different in different places. If you are curious to find out how much you weight on the moon or other planets check out the link bellow!
http://www.exploratorium.edu/ronh/weight/

After making it clear the differences between mass and weight we started to talk about objects in free fall. An object in free fall is falling only under the influence of gravity. We found out that the acceleration of an object in free fall is always gravity. That is explain by the fact that Newton's second law says a = Fnet/m. Knowing that the Fnet is the weight of the object and that w = mg rewriting the equation we now have a = mg/m. The masses will cancel out leaving a = g! Now that we established that acceleration of free falling objects is gravity we can take the 'how far' and 'how fast' equations and substitute a for g!

How fast: v = gt
How far: d = 1/2 gt2

Let's say that you want to know how tall a building is and you don't have any type of measuring instrument. What now? It's easy!  Go to the top of the building drop a ball from the top of it and record how long it took to reach the ground. Do this a few times plug in the average time for t in the how far equation and 9.8 for g! Do the math... and now you know how tall the building is!

Now we moved on to talk about projectiles. Projectiles are objects that move through air or space under the influence of gravity. We learned that when an object is not only dropped straight down it has a vertical velocity and a horizontal velocity. The two are independent of each other! Horizontal velocity will remain constant and vertical velocity will accelerate 10 m/s each second due to gravity. One of the hardest things for me to understand this unit was when to use the vertical velocity and when to use the horizontal velocity when answering questions. I learned that when you want to know how long an object stayed in the air distance from the ground is the only thing that matters! The "object  falling from a plane"  problems also gave me some trouble but after going over some quizzes I understand them a lot better. We learned how to find out the actual velocity of a projectile by using triangles and the two velocities.


Now that we know how objects behave falling only due to gravity we can talk about objects falling with air resistance! A term that is really important to understand is terminal velocity. Terminal velocity happens when the F air = F weight, the acceleration at terminal velocity is 0 and the velocity is constant! It is also important to know that there are two ways to increase air resistance:
*Increasing surface area
*Increasing the velocity

Have you ever wondered why a crumpled piece of paper falls faster than a flat one? The reason that happens is because when objects are falling with air resistance they want to reach terminal velocity that is they want their weight to equal the Fair. The papers have the same weight so they need the same Fair. The difference between the two is that one of them has a lot more surface area than the other. Because surface area increases air resistance the flat paper can move slower and still reach terminal velocity. The crumpled paper needs to increase velocity in order to increase air resistance to reach terminal velocity. The same concept of surface area applies to skydiving! If you open your arms and therefore increase your surface area you will slow down because the air resistance will  be greater! When you open a parachute the concept is the same again, the parachute will increase your surface area considerably so you will slow down considerably!

The content of this unit can be observed everywhere! Now you know why some things fall faster than others, why you can slow down and speed up while skydiving and even how a parachute works!

Unit 1 Reflection

Inertia!

On the first unit of my physics class we learned a lot about Newton's first law. Newton's first law
states that inertia is the name of the property that's states that an object in motion wants to stay in motion and an object in rest wants to stay at rest unless a net force acts upon it. It's important to remember that inertia is not the reason why objects want to keep doing what they are already doing, the reason for that is unknown and inertia is only the name of this property.  

The video above is an example of inertia. When the tablecloth is pulled from under the dishes, they don't fall on the floor because they were at rest and for this reason they wanted to stay at rest, because there was no outside force acting on them they stayed where they were.



While talking about inertia we approach other new terms such as equilibrium and net force. Net force is when more than one force acts on an object. When the net forces are balanced and for this reason they add up to 0 Newton (measure of force) the object is said to be in equilibrium. When a body is in equilibrium it can be moving at constant speed or it can be at rest.       

Speed, Velocity and Acceleration:
After talking about inertia, we moved on to talk about speed, velocity and acceleration. We learned that speed is a measure of the magnitude of distance covered in a time period. Velocity is distance in a determined time and also takes in consideration the direction of the movement, therefore even if a car maintain the same speed in a curvy road, the velocity will not be constant. Acceleration is the rate of change in velocity over a period of time. The equations that represent those terms are:


s = d/t

v = Dd/t

a =  Dv/t

Constant acceleration:

How fast v = at

How far: d = 1/2 at²

This equations bring me to what was the hardest part of this unit. Even though the equations are straight forward, learning which one to use in each specific situation was not easy. On some of my quizzes. After some time my problem solving skills got a lot stronger because I started to understand how to use the formulas correctly. I understood the concepts of inertia and equilibrium pretty easily probably because of the hovercraft lab we did on one of our first classes. The lab helped me understand that objects in motion really do stay in motion unless there is a force acting upon it.

Conection to Real life:

This unit is extremely connected to our everyday life. Who never forgot something on top of a car and took of? Have you ever stopped to observed that the object is at the same place it was before but on the ground? This concept is explained by Newton's first law! The object was at rest and therefore wanted to stay at rest, there was no outside force to stop it from doing so therefore the object continued in the same place but on the floor. This is just one example of many situations that can be explained by inertia!