71 Roller Coasters-Mid

Roller Coasters FOCUS Question How do forces make a roller coaster car move along its track?

The Thrill of the Ride Ka-thunk! The restraints press down across your body, holding you down in your seat. Ka-CHINK-chink-chink. The small car lurches forward and you start to climb up, up, up, up to dizzying heights. For a moment, at the top of the world, you feel you can almost touch space. Then the world falls out from under you, and you plummet toward Earth. Your skin tingles and you scream and laugh as the ride picks up speed, thundering down the track. Your roller coaster ride is two to three minutes of mind-bending, gut- sucking forces and nonstop changes in acceleration. Roller coasters put Newton's laws of motion into action! Let's explore the physics that make roller coasters fun.

Riding with Newton At the beginning of the ride, you climbed into a coaster car, eager for it to start. Did you know that even before the cars moved, the laws of motion were already at work? Newton's law of inertia says that an object at rest will remain at rest until a force moves it. It also says that an object in motion will stay in motion until a force stops it. The measure of an object's motion is called momentum. On most roller coasters, a motor makes a chain pull the car up that first hill. The motor and chain provide the force to overcome the car's inertia.

The Lift Hill When the car pulls out of the station, it is immediately pulled up a huge hill. Why is the hill so high? That first hill lifts the car to its highest point of the whole ride, which is why that hill is called the "lift hill." Way up there, the car has the most potential energy, or stored energy. Gravity is always pulling the car down toward the ground, and the lift hill gives the car a long way to pick up speed as it rolls down. Believe it or not, most roller coasters only use motors to get the car up the lift hill. After that, it rolls—or coasts— the rest of the way due to gravity and inertia.

Picking Up Speed Once the car tips over the hill, it speeds down the track. The potential energy the car had at the top changes to kinetic energy, or the energy of motion. It quickly accelerates or gets faster and faster. At the bottom of the hill, most of the car's potential energy. has changed to kinetic energy You quickly start climbing another hill. It's not as tall as the first one, but it's still pretty high. As the car climbs, gravity pulls down on it, reducing its speed. The car's momentum carries it up to the top of the hill. The car's kinetic energy changes back into potential energy as it climbs the second hill.

Loopy Down the hill and up ahead, the track seems to turn upside down. So does your stomach! How will the car ever get through that loop? The car is moving very fast when it enters the loop; it still has a lot of momentum. The car's kinetic energy changes back to potential energy as it rolls up the loop. But what happens next? Gravity pulls on the car, and potential energy switches to kinetic energy once more. Down the loop you go! Do You Know? Roller coaster loops are often shaped like an upside-down raindrop. With a steeper slope at the bottom. the car enters and exits the loop faster than it would in a circle.