- Inertia (Newton's First Law)
- Equilibrium and Net Force
- Speed and Velocity
- Acceleration and Constant Acceleration
- Graphing Data and Using Linear Equations
INERTIA
Inertia can also be referred to as "Newton's First Law". This law states that
- An object in motion will stay at motion and an object at rest will stay at rest unless acted upon by an outside force
To remember this, Mrs. Lawrence told us that all objects are "lazy". Objects don't want to change what they're doing unless a force acts upon them to do it for them. A force is a push or pull on an object, measured in Newtons (N).
The diagram above is an example of an object in motion staying in motion. The ball, along with the cart, are both moving at the same speed. Once the ball is ejected from the cart, it continues in the same path as the cart because there are no forces causing it to slow down. therefore, it lands in the same spot along with the cart in motion.
Another example is dishes placed on a tablecloth on a table's surface. If someone were to pull the cloth from underneath the dishes, they would stay in the same place on the table rather than crashing to the ground. This is because they were at rest on the table, and although the table cloth has a force causing it to move, the force is not applied to the dishes, so they remain on the table.
One important thing to remember about inertia is that it IS NOT A FORCE. Inertia is simply a property of motion. If a question asked:
- You throw a ball upward, what causes the ball to continue to move upward?
The answer IS NOT inertia. The answer is, there is NO force causing it to move forward. All objects simply have the property to stay in the motion they are given.
Also, inertia is related to the mass of the object. Simply put, inertia increases as mass increases. A tennis ball traveling at 20 mph will be easier to move/stop than a 300 lb. wrecking ball.
Here is a video created by me and two of my classmates explaining the property of inertia:
Also, inertia is related to the mass of the object. Simply put, inertia increases as mass increases. A tennis ball traveling at 20 mph will be easier to move/stop than a 300 lb. wrecking ball.
Here is a video created by me and two of my classmates explaining the property of inertia:
EQUILIBRIUM AND NET FORCE
A force is the push or pull exerted on an object, measured in Newtons (N).
The net force of an object is the result of 2 or more forces acting upon an object (also measured in N).
This example shows 2 separate forces of 5 N being exerted on one side of a box. To calculate the net force, you add the forces because they are in the same direction 5 + 5 = 10. Therefore, the net force on the box equals 10.
However, if 2 forces are directed on an object from opposite directions, it's possible that they can equal out to give an object a net force of 0 N. This is know as the state of equilibrium.
The example above shows equilibrium. Because there is a force of 5 N being exerted on the object from opposite sides, 5 - 5 = 0 , the object's net force has been equaled out and is now in equilibrium, at rest.
An object can be in equilibrium in 2 ways
- at rest (as showed above)
- in motion, at a constant velocity, which is explained in the next section
Speed, as most commonly know, is how fast an object is moving. Velocity is similar, however there is one important difference. Velocity is "direction aware". Velocity is the speed of something in a given direction. If an object's direction is changing, so is the velocity. In order for an object to maintain a constant velocity, it must also maintain the same direction. However, an object can maintain a constant speed while changing direction. Therefore, an object changing direction is always changing velocity, even if it's keeping a constant speed.
In order to find an object's velocity, one must know it's distance and time. They can then calculate the velocity with the following equation:
You can also calculate the distance an object moved if given the velocity and time, or how kong it took given the velocity and distance.
Velocity and speed are both measured by the unit meters/second.
ACCELERATION
Acceleration is the rate at which an object is speeding up. this can be calculated by the following equation:
This equation reads, "acceleration equals the change in velocity over a time interval".
The acceleration of an object can be constant, increasing, or decreasing depending on the slope of the plane it's traveling on. These slopes each give the ball a different acceleration:
Notice how the acceleration of the last graph is decreasing. Remember, although the acceleration is decreasing, the object's velocity is still increasing. Even though the acceleration is going down, it is still accelerating at some rate, so the object is still going faster per second.
The example above shows a ball rolling down a slanted plane. As you can see, at each second interval, the ball increases it's velocity by 7m/s. Since this is happening per second, you must write acceleration as m/s². This is the unit you will always use to describe acceleration. One constant you should remember is that an object at free fall will always have an acceleration of 10 m/s². Also, an object moving at a constant velocity across a plane will have no acceleration 0 m/s². This brings us back to the state of equilibrium!
There is a different equation for finding the distance traveled by an object when given constant acceleration:
GRAPHING DATA AND USING LINEAR EQUATIONS
You can graph the data from an acceleration experiment by using time as the x coordinates and distance as the y coordinates, like we did in the "constant Velocity versus Constant Acceleration Lab". Once you graph your data, you can use Excel to determine the equation of the line your data formed. The equation of a line is:
The equation used for distance and acceleration is :
In an experiment, the "b" value of the equation is usually so close to 0 that it can be omitted. Therefore, one can deduct that:
The y coordinate is the distance, the (1/2a) is the slope, and the x coordinate is the time. Knowing this is important because you can take the slope from your equation (calculated from Excel) and set it equal to (1/2 a), allowing you to solve for a, giving you your acceleration!
REFLECTION
What I have found difficult...
- In this unit, I found it hard to understand how to translate an Excel graph's line into the equation of constant acceleration. I wasn't sure how Excel graphs translated into the data we were retrieving from our experiments
I overcame these difficulties when, on the board, Mrs. Lawrence wrote one equation under the other and showed how the variables line up and how you can then solve for acceleration knowing the slope of the line. That's when it all clicked why we were plotting our data onto excel and creating this line.
At first, I feel like I didn't have a clear understanding of the formulas for acceleration, velociy, etc. I confused them and had trouble solving problems using equations. However, I made a list of these formulas and clarified them and now solving with them is simple. At the beginning of the unit, I was skeptical of blog posts and why we do them. However, I understand now that it's like making our own study guides as we go along. Reading through my blog posts from the unit, I was able to remember each class, what we learned, and how well I learned it. I was able to decide what I need to study more and what I have concretely understood. I think I've already improved since the first week of class. As far as my group's Inertia video, I think I gave as much effort as I possibly could, and even got excited about the subject. And with this unit reflection, I feel confident in my explanations, and ready to explain concepts to anyone else who needs an explanation. Looking back at my class notes helped me a great amount while writing my reflection, so I think my in-class listening skills have also benefitted my understanding of the unit.
My goal for he next unit is to never miss watching an assigned video. The videos assigned help me understand the textbook's context on a deeper level, especially because I take notes and then answer questions with these notes. This system if fool-proof and if I don't miss any video assignments next unit, I should have a thorough understanding of all the concepts.
CONNECTIONS
When I was driving, I began traveling down a slight slope. I noticed that the car was still accelerating, however, I was not pressing the gas pedal. Therefore, my acceleration was not increasing, however my speed was still increasing. I realized that although my acceleration may have been decreasing (because I took my foot off the gas), the car was still in a state of acceleration, therefore the speed was still increasing.
