QUESTION #199

# I am 11 yrs old and soon to be going to Magic Mountain to ride a roller coaster for the first time. My Dad says that I really don't need a safety harness when the roller coaster goes upside-down because centrifugal force will hold me in. Is this true?

Asked by: Jesse Underhill

### Answer

Your Dad is a very smart man! He is correct when he says that for the time that you are upside-down you do not need your harness to stay in your seat. Centrifugal 'force' will hold you in your seat. However, for the rest of your ride you do most certainly need your harness so do not, under any circumstances, ever take it off!

Now, let's talk about what is going on during your roller coaster ride. Let's start with the loops. As you go into the loop the car begins to turn upwards. But, because you have mass you have inertia. Do you know what inertia is? Have you ever run after someone going really really fast and just as you are about to catch them they turn and you keep going straight? Even if you tried to turn you would still be going straight for a while. This is inertia. Inertia is the tendency of an object to keep doing what it is doing. So, if an object is going in a straight line it tends to want to keep going in a straight line. This is what happens to you on the roller coaster. As the car goes up into the loop your body wants to keep going in a straight line. This is the 'force' you feel as you go into a turn, any turn. The word force is in quotes because there is not really a force pushing you into the car. You feel this push because of your inertia. So, at the moment you are upside down your body still wants to continue motion towards the track.

It is very important, especially on a roller coaster, to understand that while you are in this loop your inertia gives you the feeling of being pushed outwards from the circle. Why? Because for the rest of the ride the designers take advantage of your inertia to make the ride more exciting. By making the car take a sharp turn you feel a 'force' pushing you towards the outside of that curve; most people think this is fun. Then, when you come down a long and steep hill the ride suddenly curves upwards and guess what you feel? Right! Your body's inertia is still causing you to feel like you are being pushed downwards even though the car has started going up. Some people love this too! Then there are those places where you top a hill at breakneck speed and suddenly plunge straight down but your body, because of inertia, is still going up! Yikes! I'm having a heart attack just writing this! I hope you have lots of fun at Magic Mountain! Keep that harness on!
Answered by: Tom Young, M.S., Science Teacher, Whitehouse High School, Texas