Danielle's Physics Blog

Mousetrap car

dlaroyphysics — Mon, 15 Mar 2010 05:54:41 +0000

On your blog, comment on how angular momentum impacts the design of your mousetrap car. WHERE in your design does angular momentum exist, and do you want to maximize or minimize the angular momentum in these locations? Finally, distinguish between the concepts of rotational inertia and angular momentum.

Angular momentum exists in the axles and therefore the wheels of the mousetrap car. It is important to consider the angular momentum in the car’s design because I want to maximize the angular momentum, so that the car continues to roll after the mousetrap has snapped. As such, it is important to think about how I will attach the string so that it doesn’t interfere with the rotational inertia (the tendency that the car will have to keep rolling after the torque is applied).

Rotational inertia is an object’s resistance to any chance in its state of rotation. Angular momentum is the product of an object’s rotational inertia and rotational velocity about an axis.

Earth as a Closed System?

dlaroyphysics — Thu, 11 Feb 2010 06:33:05 +0000

Earth, unlike the universe, is not a closed system because energy is constantly entering through the atmosphere and being trapped in by the greenhouse gases. While this may not initially seem reasonable because Earth is often referred to as a “system”, it is not a closed system which is the pivitol part of the Law of Conservation of Energy. Earth’s energy is constantly changing due to solar energy that is entering every moment, and because of this, we can see that Earth still abides by this law.

Momentum and Kinetic Energy

dlaroyphysics — Wed, 03 Feb 2010 06:43:56 +0000

Compare and contrast the concepts of momentum and kinetic energy, being clear to note how they differ from each other on a purely conceptual level.

Similar: Both kinetic energy and momentum are properties of objects in motion.

Differences: Momentum is a vector, which implies that it indicates direction as either a positive or negative.

Kinetic energy on the other hand, is a scalar which means it is never negative (only indicates magnitude). Because of these properties, momentum can be cancelled out in the collision of two equal but opposite travelling objects. However, kinetic energy will never cancel out in a collision, it will only increase, because the energy amounts are always positive.

Both Similar and Different: Kinetic energy is equal to (1/2mv) squared while momentum equals (mv)

Elastic versus Inelastic Collisions

dlaroyphysics — Mon, 01 Feb 2010 06:19:20 +0000

Elastic Collisions: The kinetic energy in the collision is conserved as the objects hit eachother and bounce off.

Inelastic Collisions: The kinetic energy in the collision is not conserved because the kinetic energy is converted or changed into another form/type of energy. When these collisions occur, the objects hit eachother and do not bounce off.

Missed Post!

dlaroyphysics — Mon, 01 Feb 2010 06:15:16 +0000

*This post was saved to my drafts instead of being posted immediately! Sorry Ken*

As the spring oscillates up and down, the kinetic and potential energy is always exchanging such that the amount of energy in the system remains constant but is split in differing amounts as it moves. When the spring is at the highest and lowest points, the spring has only potential energy (gravitational and elastic respectively). However, as the spring moves between the two points, there is some potential and some kinetic energy. Specifically, as the spring extends from the top to the midpoint, the potential energy decreases as the kinetic energy increases. Then, as the spring uncoils past the midpoint, the kinetic energy decreases as the energy becomes potential again.

Global Warming and Energy

dlaroyphysics — Tue, 26 Jan 2010 05:47:29 +0000

Global warming does not contradict the law of conservation of energy because energy is not being created in the system. Instead, energy is entering the system via the sunlight as it always has, but the difference now is that human emissions of carbon dioxide are changing the make-up of the atomosphere which the heat energy used to be able to escape from. While it may seem like humans are “creating” carbon dioxide, it is merely that we are converting mass, such as natural gases from the earth into energy and carbon dioxide. Because of these two pieces, the energy is clearly, in no part of the global warming process, being created within the system, but rather merely added by the sun as it always was.

Light Interactions with Matter

dlaroyphysics — Fri, 15 Jan 2010 08:54:29 +0000

When light interacts with matter, we tend to see colors as a result of the reflection of certain rays and absorption of others. Matter has atoms with certain vibration frequencies which, when they match the vibration frequencies of the light waves, allows the electrons to become excited by the light and “absorb” it. When these electrons are excited by waves that match their natural vibration levels, they excite the atoms around them causing heat from the absorption. When the light waves do not match the vibrational frequencies perfectly, the matter reflects, meaning that rather than vibrating at the high freqency as it would if it matched, the electrons vibrate quickly for a short time and the energy is put back again as a light wave.

How the Earth was Formed

dlaroyphysics — Mon, 11 Jan 2010 17:27:02 +0000

According to many scientists, the Earth was formed by a series of high speed collisions of smaller space matter which continually melded together (after collision). This created an extremely hot body of rock and as the collisions slowed down, the earth began to cool, which formed a small crust on its surface with a liquid molten material that formed the inner core. As it continued to cool, water vapor began to condense which allowed water to begin accumulating. Scientists believe volcanic activity and gasses which escaped from the inner layers of the earth formed the atmosphere of the earth and allowed for the eventual life on earth.

Homework due 11/20/2009 Air Bags

dlaroyphysics — Fri, 20 Nov 2009 04:58:00 +0000

Because Newton’s first law of motion expresses that an object in motion will remain in motion at a constant speed in a straight line until acted upon by an outside force, when a car crashes, inertia will keep everything inside the car in motion at the speed that the car was travelling when a car crashes. While the momentum of the car stops immediately, the momentum of everything in the car (people included), carries the contents of the car forward even after the impact of the crash. Because of the close proximity of the driver and passenger to the dashboard/steering wheel and the great impulse (change in momentum) after the impact of the car crash, the job of the airbag is to prevent injury in a short amount of time. This means the airbag must counter the momentum of the people in the car to slow them before they are hurt by the impact. This is why the airbag inflates so quickly. It must absorb the momentum and slow the person down rather than allowing the person to hit the solid dashboard and risk likely injury.

Conclusion of Skateboard Experiment

dlaroyphysics — Tue, 03 Nov 2009 06:54:57 +0000

Result:

0.54 m/s = accelleration of the skateboard
Does not appear valid simply by reasoning/common sense

i. Our accelleration shouldn’t exceed the kinematics equation result

ii. Kinematics equation result: .47

iii. Only a .7 m/s differnece but the fact that this is a + difference is an issue because there is nothing but human error that would increase the acceleration past that of the hypothetical world of kinematics which has no gravity or friction.

1. Errors:

i. Human error of stopwatches stopping at same time

ii. Road error: ie. the road was not fully smooth, there were holes, and there was friction whereas the kinematics equation assumes a frictionless environment

Example of human error from results: the average velocity should not decrease at any point in the skateboard’s travel but the speed decreased by almost 2 meters per second between 10-12 meters.
Slope of hill may not be constant all the way down.

The result acquired in this experiment was 0.5413 meters/second, which is about 0.7 m/s greater then the aceleration of the skateboard this is derived in the kinematics equation X_f= X_i+ V_i t + (1/2)at²While these figures are fairly close (less than a 20% difference) and initially appear valid, the results indicate a prevalent margin of error on the part of those who performed the test and because of this, they are invalid. The kinematics equation indicates that the acceleration should only be .4747 m/s. It would be reasonable if the acceleration figure derived from the experiment was less than this acceleration, but it is unreasonable to have an experiment which yielded a greater acceleration than the equation did (as this experiment yielded). The kinematics equation does not consider friction that exists in the real world, nor does it account for the road’s imperfections (because it was not perfectly smooth), which would both result in a slowing of acceleration that should have occurred in the experiment. Because the results did not match the slowing of the acceleration that would be expected and instead reflected the opposite, it is clear that the human error in timing affected the results of the experiment, and thus the results are not valid.

The human error that occurred must have had a large impact on the data collected and the acceleration that was determined for the skateboard, because this is the only reason the experiment’s acceleration would be greater than that from the kinematics equation. To fix this, a device which started the watches at the same instant and was able to accurately record the times at each mark would be required (such as a radar detector at each marking). Additionally, it would be easier to analyze the results if measurements had been taken more frequently, perhaps every meter instead of every 2 meters, so that the chance of outliers would decrease and the line of best fit for the velocity/time graph would better fit the points gathered. Because there is a possibility that the hill was not perfectly constant all the way down, and there was significant human error, the experiment would be improved by resolving these issues in a better-controlled, mechanically monitored environment.