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!
