Speed, Distance, and Time: Experimenting With Acceleration And Velocity

Constant velocity occurs when an object is moving at the same speed and in the same direction; constant acceleration occurs when an object is changing speed at a constant rate. If an object is traveling at an increasing acceleration, its velocity will increase as well. Likewise, if that object is traveling at a decreasing acceleration, its velocity will also be decreasing. An object, however, cannot have both constant acceleration and constant velocity at the same time.

Along with two other members of a group, I conducted a lab experiment about constant acceleration and velocity. In this lab, we rolled a marble across a tabletop and marked the distance it traveled every 0.5 seconds using chalk. We consistently measured this amount of time using a metronome.  We used a flat surface to measure constant velocity, whereas we created a ramp to measure constant acceleration.  The purpose of this lab was to demonstrate the difference between constant velocity and constant acceleration as well as to support our lessons on these traits with data we found ourselves. Our intent was to collect data that we could present as concrete information on a graph.

The markings of the marble’s progressive movements at a constant velocity were equidistant from each other, as expected for an object, which, by definition, is theoretically covering the same amount of distance in a set time interval. Conversely, the markings we made to measure the progress of the marble moving with a constant acceleration grew increasingly further apart from each other as the marble’s journey continued. This is due to the fact that and object moving with a constant acceleration will continue to gain speed at a set rate until its acceleration changes due to the slope of the surface upon which the object moves or until it is acted upon by an outside force. We measured the distance from the starting line of the marble’s trek to each line (each of which were marked 0.5 seconds after the last) and used this information to create x and y points so we could graph our data.

The formula used for constant velocity is V=d/t (velocity is equal to distance over time) and the formula for constant acceleration is d=(1/2)at^2 (distance equals one half of acceleration times time squared).

The graphed line of constant velocity was a straight line whereas constant acceleration formed a slight curve along the graph (we graphed it as a straight line for viewing purposes although the points graphed did not exactly match up with the trend line). The graphs were used to support our data by visually demonstrating the relationship between distance and time in the equations for constant velocity and acceleration. In the velocity graph, distance was shown as values on the y-axis while time was shown along the x-axis. As time increased, distance followed suit, demonstrating a consistently straight line on the graph; this displayed the marble’s constant velocity. In the graph of the marble’s acceleration, distance was again on the y-axis, but the x-axis showed values of time squared as opposed to time. Again, each of these values increased contiguously to show that constant acceleration depended on distance covered in increasingly fast time increments. These graphs supported out demonstrations of the concepts as well as our data collected.

This lab was informative in several ways. I realized in the process of marking of the marble’s movement that more often than not an experiment will need to be repeated for accurate results; in the future I will be prepared for a lab to require time. Things do not always work perfectly on the first try. In future labs I will repeat the careful notation of equations and units as it helped me immensely in my calculations during this experiment. And lastly, I learned from this lab that the experiments we conduct are not simply arbitrary activities- they do in fact relate to our studies of physics and I should work harder in the future to apply my knowledge to the lab as I am conducting the experiment.

Velocity and Acceleration

Acceleration: Calculating the acceleration of a Porshe


The video I posted above is an explanation of acceleration kindly provided by Khan Academy. Acceleration is the change in velocity over a given time interval; or you could say that acceleration is  how fast an object is changing speed. Acceleration is measured in units of meters per second squared (m/s^2). This video really goes through the steps of how to calculate the acceleration of an object and I think it is a great resource to clear up any confusion about acceleration. It is especially helpful to be able to see the instructor writing out his work on the problem with his explanation matched up in the background; this makes it easy to follow along.



After that explanation of acceleration you may be wondering, what is velocity anyway? Velocity is both the speed and the direction of an object. Velocity is measured in units of meters per second (m/s). Constant velocity can only be achieved if an object is moving at the same speed as well as moving in the same direction; for example, a runner sprinting at the same speed in a straight line would be moving at a constant velocity. The second video I have included is less serious; it is an animated little jingle about the difference between speed and velocity. While velocity measures both an object's speed and direction, speed only measures how fast something is going. I think this video showed a lot of cute examples of objects moving with constant or changing speed and velocity and presented it in a fun manner.

So, just a quick recap:

• velocity (not to be confused with speed) is an object's speed and direction 
• acceleration is the change in an object's velocity over time

Hovercraft Lab Excitement!!

Today, in class, we conducted a lab using a hovercraft to display Newton's 1st law and demonstrate inertia. In this lab we got to physically ride a hovercraft around the gym- it was so cool!

Riding the hovercraft was very different than I had expected. I had to balance out my weight and scrunch myself into the middle of the seating pad at the same time. This required some interesting leg positioning as well as awkward leaning forward to stabilize the craft. That was another thing that surprised me; I had expected the hovercraft to be stable when I was sitting on it but in actuality, it was very prone to leaning and tilting. Looking back, this is very reasonable and I probably should have expected this. It felt like I had been shrunk and was riding around on an air-hockey puck. I say this because the hovercraft encountered no surface friction (as it was not in contact with the ground like other vehicles). It rode smoothly and did not slow down at all as I glided across the gym floor. That was a little weird to experience and the best thing I can think to compare it to is the way in which an air-hockey puck glides smoothly across the air-hockey table. The puck glides smoothly because, like the hovercraft, it has air blasting it up from the table's surface to decrease the amount of friction that would otherwise slow the puck down. Riding the hovercraft was different than skiing or riding a scooter. Surface friction from the ground causes both of those things to slow down and you must exert your own force on them in order to continue your motion. Once the hover craft is in motion, no outside force is acting upon it so it remains in motion at a constant velocity until stopped - just as Newton's First Law describes. Skiing or scootering, you would encounter an outside force that would interfere with the object's tendency to remain in motion.

This lab taught us that inertia is directly related to mass. The heavier riders were harder to stop than the lighter riders on the hovercraft. This is because the more mass, the more inertia there is for a particular item. I learned that net force is the total force that act upon an object. When these forces are balanced out (opposite forces are equal), the net force equals zero; thus there would be no net force. Equilibrium occurs when these opposite forces are balanced out. For example, when the hover craft was gliding, it was not being acted upon by any outside forces yet it was moving forward at a constant velocity due to it's tendency to stay in motion. At this point it was not accelerating or decelerating and it was in an uninterrupted state of motion. This would be equilibrium. This is also the point at which one could expect to be moving at a constant velocity, according to the data gathered in this lab.
Also based on this lab, acceleration seems to depend on the force acted upon the object in rest to put it in motion. The stronger the force, the greater the rate of acceleration should be.

This was a fun inertia activity and it definitely helped me to understand how an object can move even when force is not acting upon it constantly.

Let's Talk About Inertia

In the video I posted above, some students have recorded several examples of inertia and I think they explain very clearly what Newton's first law is all about. Inertia is the property of an object to resist changes in motion. Newton's first law of motion states that an object in motion tends to stay in motion (while an object at rest stays at rest) until an outside force acts upon it. In the examples shown, inertia prevents objects from moving or discontinuing their motion. I think that the numerous different examples were very helpful in the explanation of the concept as it shows inertia working in different situations.

Physics Begins

Before I decided to take physics this year, I was very apprehensive as it is often presented as a daunting course. Now that we are starting off, I am actually pretty excited about the material. This year in physics I'd like to learn more about sports and the science behind them; I play soccer and I know physics is definitely involved. I also expect to learn about the relationship between certain forces acting in nature- momentum, velocity, acceleration- as well as different scientists who have developed theories throughout history.

Physics is an important course of study as it is a large part of our daily lives. Everything we do is possible due to certain laws of physics which I am certain to learn about in this class. Knowledge of physics gives us a deeper understanding of how other things work as well. For example, if I were to go skydiving, I would understand what is happening and why more so than I would without a basic knowledge of physics. Physics also ties into other topics of study, as it helps develop logical thinking skills.

A few questions I have about physics are:

1. How do we know certain theories are true?
2. Do the physics we are studying now apply to other places in the universe? Are the laws the same on Earth as on Mars?
3. What is the difference between acceleration and velocity?

I have a goal to get an A in physics this year. I also wish to have high effort, which is a personal goal I hold myself to in all of my classes. I think that if I work hard and put in measurable effort, there is no reason I should not receive the results I am striving for. I am aiming to actually understand the material as well. After biology, I could list off information and explain different processes to people as I observed them because I really understood what was going on. Chemistry was not the same story but I am hoping I will be able to grasp physics as well as I did biology.