Linear accelerators are large and complex scientific devices that accelerate sub-atomic particles. It is very much possible for you to design a handy magnetic linear accelerator (aka Gauss Rifle), not for small particles, rather for small metallic balls.
For this experiment, you will need a 1-foot wooden ruler with small grooves on the top, four small but strong magnet blocks, nine steel balls (5/8 inches in diameter), scotch-tape and an NT cutter or knife.
Now, on the top of the ruler, place a magnet block at the 2.5-inch mark. Use tape to adjust it so that the magnet doesn't move at all. Cut off the excess tapes from the sides using the cutter, but don't cut yourself in the process. Repeat this to adjust the remaining magnets at the 5-inch, 7.5-inch and 10-inch marks.
Next, place two steel balls on the right side of each magnet, so that they are side-by-side. The balls will stick to the magnets. Choose a target -- a plastic cup or bottle will suffice -- and place it a little apart off the right side of the ruler.
Put on safety goggles for the next part. Place the last remaining steel ball on the far left side of the ruler, but hold on to it with a finger. When you are ready to fire the gun, release the ball. You will see that the intermediary balls will move very fast, and the last ball on the far right will shoot itself off the ruler and hit the target!
Congratulations! You have successfully made a super cool gauss rifle that you can play with. However, practice caution while firing, else others may get hurt. You and your friends can now play a game of who can shoot the ball over a larger distance, which can be done by altering the length that the ball has to travel initially when you release it.
Let's number the balls, with the #1 being the ball in your hand, #2 being that attached to the first magnet, and so on as we go right. When you release ball #1, it hits the first magnet with a particular force, and transfers its energy to ball #2 through the magnet. But ball #2 is firmly attached to the magnet due to its attraction, so the energy will pass to ball #3, which will separate itself from ball #2 and roll towards the second magnet. As it goes, its speed increases due to the magnet attracting it, and the grooves facilitate the movement. When this ball hits the second magnet, all its energy will be transferred through the magnet to the balls on the right. This process goes on till ball #9 gets all the energy. Since it is on the far end and there is no other hindrance, the ball shoots off the ruler at high speed and hits the target. To accelerate the balls even more, you may try a larger ruler with more balls and magnets. Have fun with the toy!