2think about the first part of a roller coaster ride: a machine slowly pulls the cart higher and higher on a hill on the track. as the cart gets higher, it gains potential energy. objects gain potential energy by being lifted farther from the ground. potential energy is stored energy. the higher an object is from the ground, the more potential energy it has.

3when the cart reaches the top of the first hill, not only are riders’ stomachs screaming for mercy, but also the cart is at its maximum potential energy. without warning, the energy-loaded cart begins to descend the first hill. as the cart careens down the hill, it has kinetic energy. kinetic energy is different from potential energy. kinetic energy is the energy of motion. all objects in motion have this energy. the kinetic energy propels that cart down the hill. eventually, the cart will fight the forces of gravity and travel up another hill. on this uphill journey, the cart again begins to gain potential energy. the cart switched from potential energy, to kinetic energy, and back again. therefore, a roller coaster ride is just the converting of kinetic energy and potential energy.

4after the first collection of potential energy, the cart does not use ropes, pulleys, or an engine. the cart, its wheels, and the laws of science are the only things that keep carts rolling firmly down the track. the air brakes on modern roller coasters bring the cart to a safe and smooth stop. if, however, a roller coaster had no brakes, it would ultimately stop on its own. the friction between the wheels and track and the friction between the cart and the air would eventually make a coaster stop. think about a super ball. although it gains potential energy every time it goes up, it eventually stops bouncing. in much the same way, the roller coaster cart would cease to move.

which best describes the details related to the main idea of this passage?
a) the details describe the experience of riding a roller coaster and how it involves science.
b) the details focus on how amusement park owners use science and work with designers of roller coasters.
c) the details describe the parts of a roller coaster, the experience of the ride, and how science is involved.
d) the details focus on how a roller coaster is made and how the safety equipment needed to ensure safe rides is installed.