Problem: Article: The vehicle identification number (VIN) is a small number usually found on the lower lefthand side of a car's front wind shield. Before purchasing a used car, you want to make sure you examine the VIN. If it looks like it has been tampered with, the car may have been stolen. Checking the VIN is a good way to weed out scams. Once you've settled on a dealership and obtained the VIN for the vehicle, make sure you assess a car's condition. You should obtain a history report for the car to make sure it was in good condition prior to purchase.  Ask the dealer for the car's vehicle identification number (VIN). For a small fee, you can run a car's VIN through a website, such as vehiclehistory.com or CARFAX, for a report on a car's history. You do not want to purchase a car that has had multiple maintenance issues in the past. You should also request the dealer provide you with a vehicle history report. A solid dealer will not hesitate to provide the report. Look the report over for any major red flags. You do not want to buy a car with a history of breaking down, or one that's gone through multiple owners. You should always take a driving test before purchasing a used car. You want to make sure the car drives smoothly and that you like the feel of the vehicle. You do not want to purchase a car you are uncomfortable driving.  Make sure you take a long driving test. A few minutes is not long enough to assess whether a car is a good fit for you. Pay attention to seat comfort. Do you feel comfortable in this car? Does the seat work for you? Also, think about how the car drives. Do you feel comfortable handling the steering wheel? Remember, you'll be driving this car for awhile. You want to make sure you're comfortable in it. You should also check to make sure the car works. Check things like the CD jack, the interior lights, the stereo, and other aspects of the car's interior. If you're interested in the car after driving it, you should have it inspected. You can take the car to your regular mechanic and have him or her look it over to make sure it's in good condition. Unfortunately, not every dealership will allow a pre-purchase inspection. However, if you're insistent on wanting the inspection conducted, a dealer may allow it if he or she believes it'll increase the chances of a sale. If everything checks out, you'll want to make an offer on the car. Before doing so, do so more research. Once again, use sites like Kelly's Blue Book and AutoTempest to figure out the average market price for the car you're considering. You can use these pricing guides during negotiation. You'll be able to tell when the dealer is requesting an unreasonably high price for the car.
Summary: Check the Vehicle Identification Number (VIN). Get a history report on the car. Take a driving test. Have the car inspected if possible. Research the average market price for the car.

Problem: Article: Add a second nut to the hook and bring the pendulum back to where you marked on the paper the first time. When you release the pendulum, start a stopwatch and count the number of oscillations for 1 minute. Repeat the process 5 times, then calculate your average.  Notice the difference in the number of oscillations and the average between 1 nut on the hook and 2 nuts on the hook. Add another nut and repeat the experiment to see if even more mass will affect the pendulum’s oscillations. Go back to just 1 nut on the hook, bring the string back about 10 inches (25 cm), and make a mark on the paper taped behind it so you can repeat the experiment from the same distance. Release the pendulum and count the number of oscillations for 1 minute. Repeat the process 5 times and calculate an average.  You may be surprised to learn that the distance (also called amplitude) does not affect the swing rate, or number of oscillations. Try the experiment again from 5 inches (13 cm) and find the average number of oscillations to see how much of a difference the distance makes. Slide the look off of the pencil and cut off 10 inches (25 cm) of string, tie another loop, and put it back on the pencil. Then bring the pendulum back about 10 inches (25 cm) and mark on the paper where you release it from. Repeat the experiment 5 times and find the average number of oscillations to see how the length of the string affects the pendulum.  Cut off another 10 inches (25 cm) of string to see the difference it makes on the average number of oscillations. The length from which a pendulum is suspended helps determine the speed and regularity of the swings, which is why pendulums have been used to keep time.
Summary:
Add a nut to the hook to see what difference the mass makes. Change the distance to see how it affects the oscillations. Cut off 10 inches (25 cm) of the string to see the effects.