Cincy Science: The physics of Kings Island roller coasters pits gravity against centripetal force

MASON, Ohio - This year Kings Island unveiled its latest thrill ride, The Banshee. Billed as the world’s longest inverted coaster, this adrenaline rush sends riders through seven inversions at a top speed of 68 miles per hour. 

During the month of May, Kings Island becomes the ultimate outdoor classroom by offering its Education Days , when students can discover elements of math and science demonstrated by the various attractions in the park.

According to Ursuline Academy physics teacher Daniel Nieman, the experience is a great resource for educators to make principles of science accessible to students.

“It really puts what you learn in the classroom into a real life setting,” he said “You could talk all day about centripetal force, but when you go out and experience it, it actually make sense.”

Q&A with Daniel Nieman

1. So what physics principles are behind roller coasters like The Beast or The Racer?

The way all roller coasters operate is that they have to do some kind of work in order to give you enough potential energy to make it through the entire ride.

If you notice the highest hill on any rollercoaster is the first hill. Because of the law of conservation of energy – you can never go higher than that first hill. Basically it’s starting with gravitational potential energy that’s pulling you down the hill and at the bottom of the hill, that’s been changed into another form of energy, kinetic energy which is energy of motion. So when you reach the bottom you have almost all kinetic and when you start up the next hill, that kinetic begins to turn back into some potential – so it changes back and forth.

Ideally speaking, you should be able to go up just as high in the next hill, but most second hills are significantly shorter like the one on The Beast, and the reason is, you lose a lot of energy on those rides.

What happens is a lot of the energy is lost as heat because of friction and turned into sound energy especially on wooden coasters because they’re more rickety. As a result, that’s why each continuing hill gets lower and lower and you go slower and slower.

2. So roller coasters like The Banshee or The Vortex work on the same principles?

Basically, it’s the same principle as The Beast, but the truth is you don’t have as much energy loss on a metal coaster. The superstructure makes the ride smoother so you lose less energy. The other Thing the Vortex does, is it takes you through a loop and helixes and the idea behind that is the curves increase acceleration.

When you’re riding through a loop, you’re experiencing what’s called centripetal acceleration or centripetal force. Centripetal force is the force that holds the ride in the loop.

This is counter to inertia; inertia is a principle that Isaac Newton came up with that basically says objects tend to maintain their state of motion. Because of inertia, the cars would want to fly off into the air in a straight line from where it left the track. What happens is the track pushes in on the train and keeps it moving in a circle. That’s what supplies the centripetal force.

Now here’s the interesting thing. Centripetal force, the force that’s holding you in the curve is stronger than the force of gravity, so you could go without those restraints systems and go through the loop and you would not fall out.

Basically, what’s happening is the ride is pushing against you and because of equal and opposite forces, you are pushing back on the ride. So the force holding you in the circle, inertia, is actually stronger than the force of gravity – so you would not fall out. But you have to wear restraints, because you’d fall out at other points in the ride.

3. So all the roller coasters utilize hills as a way to create potential energy?

Actually, The Flight of Fear roller coaster works the opposite. It begins with kinetic energy. A large motor is used to accelerate riders from 0 to 54 mph in 4 seconds. Most coasters, you get your original energy by being drug up a hill and the acceleration of gravity is basically what runs the ride.

Flight of Fear works differently because you gain the speed from being shot up the hill. Basically it’s the same technology they use for airplanes on aircraft carriers. Normally you can’t build up enough speed to take off, so they have devices to push you forward so you have enough speed to become airborne when you leave the deck.

At Cedar Point in Sandusky, they have a ride called Top Thrill Dragster and instead of going 54 mph, you’re going over 100 mph and it makes you go up 420 feet instead of 74 feet.It goes from 0 to 120 mph in 3.8 seconds. It’s an incredible amount acceleration.

4. What about heart pounding rides, like Drop Tower?

Basically Drop Tower works on the idea of free fall. They raise you to a height of 315 feet above the ground and you fall 264 feet before the breaking takes place. Gravity pulls you down

at a rate of 32 feet per second squared and what that means is your speed increases 32 feet per second every second that you fall. As you go you continue to gain speed until a certain point.”

5. So what’s the maximum speed you reach?

“Here’s the thing you will never really reach your true maximum speed because of something called terminal velocity. If you were falling into nothingness, your speed would continue to increase 32 feet per second for every second that you fall.

When you’re falling into air it creates resistance and the air begins to push back on you. It continually pushes back, so when the force of falling pushing down and the force of air resistance pushing up become the same, you stop accelerating and you fall at a constant speed and that speed is called terminal velocity. Of course you never reach terminal velocity Drop Tower because the ride isn’t high enough.”

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