1 STEM News: Game On! BOUNCE: IT’S ABOUT ENERGY
How high will a basketball bounce when dropped from shoulder height? a. back to shoulder height b. less than shoulder height c. higher than shoulder height
If you answered “b” you are right. When a basketball is held UNDERSTANDING above the ground, it has a lot of potential energy and When a ball is dropped to the ENERGY IS A SLAM no kinetic energy. As it falls, it starts ground, it comes back up almost DUNK! losing its potential energy and gets to the point it was kinetic energy. dropped from, but not quite. When the ball hits the ground, it has lots of kinetic energy. The friction against the ground slows the ball down, but it also slightly heats the ball. This is thermal energy. The important thing The ball bounces back up but to a to remember is lower height than where it started. Drop a basketball and that energy The original potential energy was let it keep bouncing. The changes. transformed into thermal energy bounces get smaller and and kinetic energy. And that’s just smaller. The ball appears the way the ball bounces. to be losing energy, but it’s not. The energy is being changed. When Three kinds of energy: the ball hits the court, the court absorbs some of the energy. Some energy is changed into The energy of motion. Anything An object high above the Thermal energy is what is thermal energy. that is moving has kinetic ground has potential energy called energy that comes from energy, and the faster it is because of the work it took to the temperature of matter. By using your hand to moving, the more kinetic get it there and the work it will bounce, or add force to energy. do when it falls. a ball, you replace the energy that was “lost.” When a ball is dropped, its potential energy is changed into kinetic energy. An important rule is that energy can’t be created or destroyed. It can only change into different forms of energy. This is called the Law of Conservation of Energy. 2 STEM News: Game On!
THE BOUNCE FACTOR hy does a basketball bounce higher than a di erently designed balls. A lot of scienti c bowling ball? Because it is made of di erent research goes into developing the right bounce materials. A basketball is in ated with air and for the right ball. When a basketball hits the oor of made with a rubber covering that has a high bounce the court, it attens and the shape of factor. Bowling balls are Several other factors a ect the ball changes slightly. made out of hard the way a ball bounces: materials that don’t bounce. • the height from which the ball is dropped Why is bounce good for a • the ball’s level of basketball and in ation not so good for a bowling ball? • temperature Using a baseball to play basketball or a • the surface upon bowling ball to play which the ball is A properly in ated or lled ball is tennis doesn’t make sense. Di erent sports require bounced round and the molecules inside the ball quickly rearrange themselves to get back to its round shape. The energy involved in that action causes the ball to bounce. Different Surfaces = Different Bounce The surface on which a ball is attening. These softer surfaces bounced also changes shape act like a trampoline, allowing when a ball is dropped on it. the ball to bounce back higher and faster. Of course, really soft Springier surfaces, such as surfaces like cotton would Styrofoam and cork, change absorb all of the ball’s energy more as a ball hits them and and stop the ball from saves the molecules inside the bouncing back. ball from having to do as much Higher = More Bounce The higher the ball is above the ground, As a ball bounces, it warms. An in ated ball, the more its potential energy. As the like a basketball, bounces higher and faster MORE ball is dropped and gravity forces it when the temperature is warmer. This is BOUNCE downward, the ball accelerates and because the distance between the air gains speed. As the ball falls through molecules in the ball increases, helping the air, its potential or stored energy is the ball maintain its round shape when LESS converted into kinetic energy. it hits the ground. On cooler days, the BOUNCE The longer the fall, the more kinetic distance between the air molecules gets energy it gains and when it hits the smaller, causing the ball to be less in ated. ground, it bounces higher. So, it attens more when it hits the ground. 3 STEM News: Game On!
Swish! It’s Geometry Swish! The lovely sound of And, the ball safely sinks a player uses knowledge of a basketball slipping through to score. the parbolic arc to throw through the net in the the ball so that it arcs over hoop, so perfectly centered If the ball hits the rim of the and up high enough to that the ball doesn’t touch hoop, the chance of it enter the basket from the back stop or the rim. bouncing out increases. above. But to sink the basketball When this happens, a silent through the hoop, swish or A parabola is a curve, swish through the net is not, a player doesn’t throw shaped like an arch. It is the only sound you hear. the ball at the hoop. Rather also called a parabolic arc.
Scientists can calculate the ideal free-throw angle for players of di erent heights. It’s 13.75 feet from the free-throw line to the center of the basket, and a six-foot player launches the ball from about seven feet above the hardwood. That works out to a shooting angle of 51°.
Dunk Directions By increasing the height at The hoop is 18 inches in which the player launches diameter. A basketball is about the ball, it raises the entry 9.4 inches wide. angle of the ball’s parabolic arc, leaving more space If a ball is dunked straight and a higher At 90 degrees (a dunk shot) the ball will go chance of scoring. down into the hoop from straight down into the net with above (a 90 degree angle), about 4.5 inches of there is plenty of room for the extra room. ball to sink all the way through the net and score. At 55 degrees it has about 2.5 inches to spare. But when a player shoots the ball farther away from the At 45 degrees it’s down to 1.5 inches. hoop, the ball needs to be thrown up at an angle. At 30 degrees, it’s basically impossible to get the ball straight into the basket. Which basketball shot at right most likely to score? 4 STEM News: Game On!
SCIENTIST’S NOTEBOOK The Big Drop Imagine dropping a basketball from the top of these famous structures. 1. Thermal energy is energy that comes from the If the ball bounces 80% of the way back up temperature of matter. toward the top, how many feet/meters high would the ball travel for each? (We did the 2. A basketball player keeps a ball bouncing by using first one for you. Are we cool or what?) an elbow.
3. Basketballs will bounce di erently on di erent surfaces.
4. Anything moving has kinetic energy.
5. A 6-foot tall basketball player needs to shoot the ball from the free-throw line at a 75 degree angle for the best chance at making a free throw sink. 1.065 feet 1.065 (325 meters)
80% 604 feet 555 feet (184 meters) (184 (169 meters) (169 305 feet (93 meters)
STATUE WASHINGTON SPACE TRANSAMERICA EMPIRE STATE BUILDING OF MONUMENT NEEDLE PYRAMID NEW YORK Parabolic Ramp LIBERTY WASHINGTON, D.C. SEATTLE SAN FRANCISCO NEW YORK Explore potential and kinetic energy at the Parbolic Ramp station in the Chevron STEM Zone. Discover how to use energy to play a tune!