Projectile Motion Reflection

What is a projectile? What is the general path of motion? Why?

A projectile is a moving object with gravity being the only force acting on it. If there was any other force acting on the object then it wouldn't be considered a projectile. To further understand this, we shot basketballs and tracked their movement using the video physics app. We started tracking the ball at the moment it left our hands and ended it when it touched the ground. Our basketball moved at constant speed in the x direction while accelerating in the y direction. Even though it accelerates in the y direction, the x is constant so we know that the slope is also a constant. At the balls highest point on the graph it is actually not moving. It reached its peak and now it starts to move downward. 

Our free body diagram shows that the only force acting on the projectile is Fg. It doesn't matter whether a projectile is moving downwards, upwards, upwards and rightwards, or downwards and leftwards the free body diagram would look the same. 

These are my graphs:

Forces in 2D and Circular Motion

1. What does it mean to analyze forces in 2D?

2D stands for two dimensions of space. We can analyze these dimensions separately or individually from one another. This means that it has an x and y coordinate, as opposed to a 4D universe which we live in that has 3 dimensions of space and 1 dimension of time(x,y,z,t). Analyzing a force in 2D means that we need to find a height and length. A force in 1D would only have height, and a force in 3D would need to have height, length, and some kind of curve.

2. How do forces cause objects to move in a circle?

Forces cause objects to move in a circle due to their center pointing(centripetal) net force. When an object is moving in a circle, it is accelerating. Not because its speed is changing, but because its direction of motion is changing. In order to accelerate, it must be experiencing an unbalanced force(net force).


3. What does it mean to be in orbit? How do satellites orbit planets? How do planets orbit the sun?


To be in orbit means that an object follows a path revolving around another object. The gravitational force is the centripetal force, and the pull keeps the object in orbit from floating away(because there is no friction in space). When satellites orbit they are really falling to the earth. Because of gravity they actually end up moving sideways around the earth. Planets orbit around the sun in a circular motion, similar to that of the satellites around the earth.

Newtons Three Laws of Motion

Law #1: If an object is at rest or in motion at a constant speed, it will stay that way unless it experiences a net force.

Law#2: Force equals mass times acceleration, F=ma. Mass and acceleration are indirectly proportional.

Law#3: When two objects interact they exert equal but opposite forces on one another. They feel a force that is...

• The same type(typically normal, friction, or gravitational)
• The same amount(no matter how big or small, the force felt is the same)
• Opposite

Hover Disk Lab

Big Question-What gives rise to a change in motion?

The purpose of this lab was to learn which forces are pulling on certain objects, in this case two people, the ground and a hover disk, by knowing Newtons 1st and 3rd laws. We experimented with a hover disk and learned that it blows air out from the bottom to eliminate friction, allowing it to glide on smooth surfaces. Theoretically if you pushed the disk, and if the surface was infinitely smooth(and if there is no air resistance), it would glide in a straight line forever. For a while we played around with the disk and passed it along to one another, simulating the diagrams in our worksheet. We used interaction diagrams and free body diagrams to chart the forces acting on each individual object. 

In this diagram the disk is on but at rest and has not been pushed yet. The earth has a normal and gravitational force with each object, yet none of the objects are interacting with each other at this time. Its strange to think that the earth and person 1 are feeling the same force from each other but it is true!

We also drew a free body diagram as a second way to show the force between each object

involved.The arrows are vectors that represent the forces acting on the disk. 

This is another diagram we drew, but this time the hover disk is on and being caught by person 2. This is different from the first diagram because the disk and person 2 are now interacting. They have a normal force acting upon them.

Fan Cart Lab

Big Question- What is the relationship between force, mass, and acceleration?

From this lab we learned that F=ma. This means that if the mass increases then the acceleration decreases(and vice versa), to equal the force. In other words, the net force on an object is equal to the mass of the object multiplied by its acceleration. This is proven by the data we collected. Although trial 4 does not fit the pattern, we concluded that this was due to human error. 

As you can see trial 4 is the outlier, so we calculated the percent error to find out our mistakes. 

Real World Connection

I found this video about Newton's Laws of Motion applied to everyday life. I liked how it had multiple examples to show just how common these theories are in the real world, not just in the classroom. In the video it showed a game of pool. The ball would remain still and at rest unless an outside force pushes it.  Once hit, the balls move in the direction that they are expected to depending on the angles that they are hit at. It was interesting for me to see that something as simple as pool can relate to physics.

http://videos.howstuffworks.com/discovery/29421-assignment-discovery-newtons-laws-of-motion-video.htm

Impulse Lab

Big Question: What is the relationship between impulse, force, and time during a collision?

In this lab we learned about impulse, which is a change in momentum for objects in a collision. It is important to know that J stands for impulse(not jules) and that objects in a collision experience equal and opposite impulse because momentum is conserved.The formula for impulse is J= Pafter-Pbefore. 

The computer that we used to calculate velocity gave us a force time graph. From this data we were able to understand that the relationship between impulse, force, and time is J=F x t. The relationship is inversely proportional so if the force goes up the time will go down and ect. but the J value remains the same. 

Real world connection: Airbags are a good connection to what we are learning in class. It slows down the time it takes to make an impact, so the more time it takes the less force you will feel ( because force and time are inversely proportional). 

Collisions Lab

Purpose: The purpose of this lab was to learn about two different types of collisions: elastic and inelastic. In an elastic collision two objects will collide and bounce off of each other. They will have equal but opposite force. In an inelastic collision two objects will collide and then stick together instead of going different directions.  

Equation for momentum: p=mv

Big Question: Which is better conserved, momentum or energy?

We can conclude that total momentum is better conserved by looking at our data. The numbers are closer together than the stats for kinetic energy. This is because kinetic energy can be transferred into heat and sound, but momentum remains the same. 

Real World Connection: A car crash is an example of an inelastic collision. When the cars connect both feel the same amount of force but the car with the greater mass will push the smaller car farther away. 

Rubber Band Cart Launcher

Big Question:
"How are energy and velocity related?"
If the amount of energy increases, then the velocity will also increase. 

Purpose: 
The purpose of performing this lab was to be able to identify the relationship between energy and velocity using the cart and rubber bands. 

Lab: 
In this lab we stretched the rubber band back starting with 1 cm and going up to 5 cm. We put the cart through two trials of each measurement and used the photo gate to measure the carts velocity( in m/s). We then took our velocity recordings for each separate measurement and we averaged them, and then squared the average. From there we were able to graph and find a best fit line. 

Key Information:
E=1/2 mass velocity squared
E=0.2v^2
The formula for kinetic energy is K= 1/2mv^2
We learned that energy is always transferred form one place to another. 
The energy is stored in the rubber band. Without the energy coming from the rubber band the cart would not be pushed forward.  

Real World Connection:
A real world connection to the concepts we learned in class is a slingshot. The more you pull it back the  the object will fly out with more velocity.This video shows a human sling shot that shoots the kids in the air and into the water:  http://www.youtube.com/watch?v=ShFAeNdiEiA

Rubber Band Lab

Big Questions:

"How can we store energy to do work for us later?"

“How does the force it takes to stretch a rubber band depend on the 

AMOUNT by which you stretch it?” 

Purpose: The purpose of this lab was to find the relationship between distance and force by stretching a rubber band. We also learned about spring(elastic) and potential energy, represented as Us. 

Lab: In the first round of this lab we only looped the rubber band around once and measured the amount of force exerted for every centimeter we pulled the band. Then in round two we double looped the rubber band and recorded our findings in a table and chart. In each round we pulled the band from 1 cm all the way to 5 cm. We found that the relationship between force and distance in this lab is directly proportional. 

K Value/ Spring Constant: For this lab the slope of x(stretch distance) vs Fs( force in spring) is the spring force. Next we tried to figure out the potential energy of our rubber band. Our graph was in the shape of a triangle so the formula for the area of a triangle to convert it into Us= (1/2)kv. 

Real life Connection:

 A sling shot. The farther you pull back a sling shot the farther the object will go. If you don't pull hard enough, the sling shot won't produce enough energy and the object won't go far. Here is a link on the science behind slingshots-http://www.sciencebuddies.org/blog/2011/08/slingshot-science-the-physics-in-angry-birds.php