Special points of emphasis
|Kinematics gives you the tools you need to describe motion. You don't address the causes of motion in Kinematics. The causes of motion are the domain of Newton's Laws and Momentum & Impulse. Kinematics uses mathematics to describe motion using the concepts of space and time.|
For the MCAT, Kinematics is an important topic, both in itself and as a primary underpinning of Physics. Kinematics is one of the main areas from which the MCAT writers draw 'plug and chug' problems for the exam. Although there are only a few quantitative problems on a typical MCAT, one or two of them are frequently kinematics problems. In addition to practicing quantitative problems, you should encourage yourself in kinematics to imagine the model mechanical system, simple bodies moving in free space. Practice visualizing motion while conceptualizing displacement, velocity, and acceleration. Concentrate on building a mental space for mechanics as an imaginative skill, a capability that will help you throughout physics.
The Chemical Bond
Functional Groups in Organic Chemistry
The Eukaryotic Cell
Bacteria and Archaea
|Scientific understanding becomes more concrete when you can relate the scale of phenomena from the different sciences, for example, to be able to relate the distance of chemical bonds to the scale of a virus.|
Divide a meter by 1000 and you have the millimeter. Perform the operation again, dividing the millimeter by 1000 and you have a micrometer, µm (10-6 m). Divide this distance by another 1000 and you have the nanometer (10-9 m), and then by another 10 and you have reached the exceedingly small scale of the angstrom, (10-10 m) The spacial dimensions of atoms and the molecules they comprise are measured in angstroms, (10-10 m) to the degree such phenomena may be measured. Atomic radii and the covalent bonds between atoms are typically 1 to 2 angstroms.
Smaller biological molecules such as mono or disaccharides or amino acids are several to ten angstroms long, ranging upwards of a nanometer in length (10-9).
Ten times larger still are the more massive biological molecules such as the protein hemoglobin approaching 100Å. Viruses range from several hundred angstroms in size (polio at 28nm or 280Å) to several thousand angstroms (smallpox at about 2000Å), which is also the scale of smaller organelles such as ribosomes (so viruses and small organelles range from hundreds to several thousand chemical bonds in diameter. Try to picture it!) If a virus were laid out on your desk, scaled up to the size of your desk, you would just be able to make out the individual atoms like grains of sand.
Bacteria range in size from 1000Å (100nm or 0.1µm) to more than 50,000Å (5000 nm or 5µm), which is also the scale of mitochondria. The scale of bacteria and mitochondria are among the smallest objects which can be viewed by the light microscope (the visible light range is approximately 10-7m or 0.1µm). Small eukaryotic cells, such as red blood cells or human liver cells, are approximately 10µm in diameter.
Larger cells such as an amoeba are 100µm in diameter (0.1 mm). At 1 mm in diameter, fish eggs can be seen by the naked eye. Now we have reached the spacial scale encompassing the phenomena of 'every day life'. We can continue panning back to see the room, measured in meters, the town, measured in kilometers, and the solar system, measured in millions of kilometers. In the vacuum of space, the distance travelled in one second by light is 3 x 108 m, or three hundred million meters (three hundred thousand kilometers).
|Before you start to work with the Interdisciplinary Discussions for a Main Sequence topic, such as Kinematics, you need to be sure that you have already achieved the Learning Goals for this topic. For Kinematics, in other words, you should already have achieved the following goals:|
1) Be able to define displacement, velocity, and acceleration in clear, conversational language.
2) Be able to reproduce the four equations of kinematics from memory and achieve facility in solving straightforward quantitative problems.
3) Be capable of explaining the difference between vector and scalar quantities and perform basic vector operations.
4) Understand how to describe how an object may accelerate yet still have a constant speed.
5) Be capable of fluently applying the concepts of uniform circular motion and projectile motion for problem solving.
For this Discussion, let us take some time to think about how Kinematics fits in with another portion of basic Mechanics, Dynamics (i.e. Newton's Laws and Momentum & Impulse). Kinematics is the art of describing motion. Later, when you progress from Kinematics to Dynamics (i.e. Newton''s Laws and Momentum & Impulse), the concept of force will enter the discussion.
This is a primary conceptual movement in basic mechanics. In Kinematics, you discuss how an object is accelerating. In Dynamics (Newton's Laws & Momentum & Impulse), you discuss why an object is accelerating.
As you progress through this course, carrying out numerous cycles through the material, every time you see the outline of the subtopics of mechanics, you want to keep that in mind as a conceptual organizing principle. Kinematics is about describing motion. Dynamics is about describing interactions.
In Dynamics, you will learn that if an object is accelerating, a force must be acting upon it. The kinematics of an object (its state of acceleration) results from its dynamics (the interactions of the object and other objects in its surroundings). Newton's First and Second Laws are directly concerned with the relationship between motion and force. Every acceleration is caused by a force.
This is a favorite idea for MCAT questions arising from fundamental mechanics. If a particle is accelerating, a force must be acting on it. As soon as you encounter the concept of acceleration, ask yourself 'What is the force?'