Physics and calculus are the two high-school subjects that impress admissions personnel the most. Calculus is the first college-level math course and physics is a student's first hard-science course. By "hard," I don't mean "difficult." Chemistry, which is usually taken before physics, is plenty hard enough for most high school students. By "hard science" I mean rigorous experimental science.
Biology is still mostly a descriptive science. You observe creation in varying levels of detail and learn the terminology used to describe it all. If you get into mathematics in a biology class, it is the imprecise mathematics of statistics. When you measure things in biology class, it is only to determine some average value - average height, average size of a cell, average lifespan, etc.- and to determine how much variance there is from that value. If you conduct a biology experiment, you have to use statistics to determine if your results are significant.
Chemistry is a semi-hard science (a firm science?). It has to deal with the real natural world also, and though elements and compounds can be precisely measured and can be shown to behave consistently once you know the rules, the world of chemicals still pitches you a curveball every now and then. For example, water expands when it freezes unlike almost every other substance. There is a perfectly scientific explanation for that, of course, but chemistry doesn't predict the phenomenon, it just explains it after the fact.
Physics, once you observe a pattern, and devise a formula, can use the formulas to predict the behavior of things before they are observed. Using physical laws and mathematics, Einstein predicted that the path of light that passes close to the strong gravity of a star will be bent. Scientists tested his prediction during a solar eclipse and were able to measure that his predictions were correct. If you know the speed and direction of a bullet coming out of a gun, you can predict where and when it will hit the ground.
One of my mathematics professors put it this way: Biologists want to be chemists, chemists want to be physicists, and physicists want to be mathematicians.
Why Take Physics?
Most states don't require a student to take physics. Two lab sciences are enough, and physical science and biology - or biology and chemistry - will suffice. Still, there are a couple of good reasons for taking physics in high school.
The most common reason for taking physics is that you plan to go to engineering school. MIT, for example, recommends a year of physics for its applicants. Rensselaer Polytechnic Institute requires three years of science: usually biology, chemistry, and physics. University of Missouri engineering departments require three units of science, at least one of which must be a laboratory science, such as earth science, biology, chemistry... or physics.
A second reason to take physics is to avoid having to take biology. If you need two lab sciences to graduate or to meet the entrance requirements of your desired college and you don't like biology, physics is a good substitute. You might also want to substitute physics if you are a non-believer in evolution and the college of your choice will not accept any biology course that is not evolution-based.
A third reason to study physics is because it is "neat," both figuratively and literally. Physics demonstrates that the real world is a well-designed place. Certain constants stay constant, like the gravitational constant and absolute zero. Things move and attract each other according to simple mathematical equations.
Chemistry experiments can be dangerous and messy, and the results can be spoiled by spills or by impurities in your chemicals. Any hands-on biology experiment involves cutting open some dead animal, mashing up plant or animal tissue, or handling potentially dangerous bacteria. Specimens may be uncooperative so that when you put them under a microscope they are nowhere to be found. Experiments in physics usually result in data that illustrates the principle, and use equipment that can be put cleanly away after the experiment.
Which Physics Course?
High school physics can be taught two different ways - the AP physics way and the nonAP physics way. AP Physics C corresponds to college physics for engineers, tends to derive formulas, and uses mathematics up through basic calculus. AP Physics B is still Advanced Placement and is similar to college physics for health professionals. For Physics B, you need to be agile in second-year algebra and trigonometry, but you don't need calculus. You may receive college credit and/or fulfill your basic physics or science requirement in college if you get a sufficiently high score on the AP Physics exam. Check with your intended college(s) for their AP policies.
Non-AP physics merely earns a high-school science credit and can prepare you for the SAT II Physics test. The only reason for non-AP physics is that you haven't done calculus or you're not up to learning calculus concurrently.
If possible, do AP (either B or C). Colleges are much more impressed with AP courses.
You will need to arrange to take the AP exam at a local school in May. It is only offered once per year.
If you intend to pursue one of the health professions - medical doctor, optometrist, chiropractor, or dentist - you will need a year of college physics as a prerequisite for professional school. If you intend for your AP test to stand in place of introductory college physics, you should plan to take a year of more advanced physics at college. Also, some colleges only give pass/fail grades, either just in freshman year or all the time. Be sure to insist on a letter grade for all your professional school prerequisite courses, because those schools count a pass as a D.
How Should You Learn Physics?
There are lots of ways for a homeschooler to learn physics. The first method is the traditional homeschool way - buy a physics home-study course, complete with textbook and any associated workbooks, test books, answer keys, and lab materials. Then take the course self-study under the guidance of Mom or Dad.
Courses are available for homeschoolers from Alpha Omega Publishers, A Beka Book, BJU Press, Keystone National High School, Saxon Publishers, and many others. Some of these have labs; for others, you will have to buy a kit separately. You can also get textbooks from secular publishers. A word of caution: Try to get a teacher's manual with an answer key and solutions to the problems. The alternative is that the home teacher has to work out all the problems himself and compare answers with the student, and not many homeschool teachers have the time to do this.
Most publishers who are used to dealing with homeschoolers will sell you a teacher's manual. Getting a teacher's manual for a public school high-school text may be more difficult. The last we heard, Ebay and Amazon will not sell teacher's manuals. HSLDA has a members-only forum for buying and selling textbooks, including teacher's editions.
Online courses are available to teach AP physics. University of Nebraska-Lincoln Independent Study High School (UNL-ISHS), for example, has Physics 1 and Physics 2 courses. University of Missouri-Columbia also has online physics courses. To find these and others, use the search arguments "online high school" and "physics" on your favorite search engine.
A third option is software home study courses. One example of this is Digital Interactive Video Education.
A fourth alternative is dual enrollment. A student attends a local college and receives both high-school and college credit for the courses taken. If you intend to take dual enrollment physics, you may have to plan ahead. For example, our local community college requires college algebra as a prerequisite for physics, so you have to make sure you take college algebra or equivalent before the semester you want to start physics.
Since the better colleges tend to want your high-school science courses to be lab-based, I advise you to make sure your Physics course has a serious lab component. Some of the alternatives I've mentioned have optional lab kits - e.g., UNL-ISHS. Major textbook publishers often offer lab supplies or you can purchase lab experiments and supplies separately, to use with the Physics course of your choice.
Physics lab kits are available from www.wardshomeschool.com and from www.labpaq.com/product-overview/physics-overview-page and others. Try keywords "physics lab kits" in your browser.