# Shooting hoops – laws of motion in basketball

Shooting hoops – laws of motion in basketball – includes related experiment on forces and female basketball players

Lynda Jones

The Orlando Magic’s Shaquille O’Neal speeds down center court. But he’s blocked by the Houston Rockets’ Hakeem Olajuwon. Shaq fakes, turns, and spins toward the basket. In a flash he soars toward the hoop. Slam dunk! He scores.

Hakeem gets the rebound and heads for his team’s hoop. Still meters away from the basket, he jumps over the heads of defensive players and sinks the ball.

As Hakeem comes back down to earth, you have to wonder–how do these star players rack up all those points?

I decide to find out for myself. So I track down Peter Brancazio, a physicist at Brooklyn College in New York, who also happens to be an expert on sports.

USING THE LAWS

Practice, practice, practice, he says. Plus, he adds, basketball players–whether they know it or not–are experts at using the laws of physics.

Really?

Sure, says Brancazio, they use these laws every day to help them sink shots. For example, when Shaq (or any player) launches a ball toward the basket, he needs to apply a force to the ball. Without force, a push or pull, the ball wouldn’t move at all, Brancazio says.

That’s because an object at rest will stay at rest unless acted upon by an unbalanced force–a push toward the basket, Brancazio explains. Another name for this “first law of motion,” described by physicist Isaac Newton in 1665, is the law of inertia, Brancazio says.

OK, I think. That makes sense. When you push something like a ball, it moves.

But then Brancazio slips in the other half of Newton’s first law: An object in motion will stay in motion (in a straight line, at a constant speed) unless acted on by an unbalanced force.

Does that mean that once Shaq launches the ball it should sail on forever–unless the “force” of another player gets in the way?

Not quite, says Brancazio. Though another player could certainly stop the ball with a force, he explains, there are already other forces at play. For basketball players, the most important force is gravity, Earth’s “downward” pull on all objects around it. On the court, players might launch the ball upward, but gravity is what pulls the ball downward through the hoop, Brancazio says.

SHOT-CLOCK ANXIETY

Of course, the closer you are to the basket, the easier it is to slamdunk the ball. That’s because “the farther away you are, the more force you have to apply to get the ball to the basket before gravity pulls it down,” Brancazio says.

So when Hakeem gets the ball on a rebound, he wants to get as close to his own team’s hoop as possible before taking a shot. But as he charges toward the basket, he’s blocked. He takes a chancy shot from nearly 4 meters (12 feet) away.

The trick when shooting from a distance, experienced ballplayers know, is to give the ball an extra push. That extra push, says Brancazio, accelerates the ball–gets it moving faster to cover the distance to the basket. This shot is a clear demonstration of Newton’s second law of motion: Force = mass x acceleration, Brancazio explains. Or, the more force you apply to an object, the faster the object will accelerate. With the extra push, whoosh! Hakeem sinks the shot.

UP, UP, AND AWAY

But getting a clear shot can be a challenge, especially if you’re being blocked by someone who’s 2.4 meters (7 feet, 1 inch) tall, like Shaq. Here’s where jumping can help you get over the heads and waving arms of defensive players. For example, when Hakeem wants to place his shot over Shaq’s head, he sends himself skyward. Here, says Brancazio, Hakeem is using Newton’s third law of motion: For every action, there is an equal and opposite reaction.

In other words, Brancazio explains, Hakeem pushes with the muscles of his legs, exerting an “action” force on the floor. The floor, believe it or not, pushes back–with just as much force. This reaction force is what propels Hakeem’s body up into the air and toward the basket, Brancazio says.

The bigger the force Hakeem uses to push off, the bigger the push the floor will give him–and the higher he’ll go, says Brancazio. So having strong leg muscles can really send you flying.

HOOP DREAMS

The point, says Brancazio, is that you don’t have to be a pro basketball player to have Newton on your team. Whenever you jump or launch a ball toward the basket, you’re using the laws of physics too. So the next time you’re speeding down center court, take advantage of Newton’s laws of motion to set, place your shots, and score.

RELATED ARTICLE: GIRL POWER

Professional basketball players aren’t the only ones who use physics to play a mean game of basketball. The University of Connecticut Huskies, the 1995 women’s college champions, have mastered Newton’s “hoop rules” too. The team used Newton’s laws to rack up 70 points in their victory game last April. List three ways Husky Jennifer Rizzotti (above) is using the laws of motion in this picture. Then get your hands on the power of Newton’s laws by trying the hands-on activity at right.

RELATED ARTICLE: HANDS-ON

SCIENCE

Forces at PLAY

Try this “moving” experiment to see how forces keep a basketball in play.

WHAT YOU NEED:

* measuring tape or meter stick

* pen

* basketball (or other bouncing ball)

* partner

* paper

* video camera and VCR (optional)

WHAT TO DO:

1. Stick a long strip of masking tape vertically on a wall, reaching from above your head to the floor.

2. Use a pen and measuring tape or meter stick to mark measurements on the tape, starting at the floor.

3. Grab a basketball in your hands and stand next to the wall “ruler.” Have a classmate “observer” stand next to you.

4. Drop the ball to the ground and let it bounce so your observer can spot how high it bounces alongside the ruler. (If you or your school own a video camera, have your partner film your experiment. Then replay the video in slow motion to get a more accurate measurement of bounce height.) Record bounce height.

5. Repeat Steps 3 and 4, only this time give the ball a light downward push instead of just dropping it. Observe, measure, and record bounce height.

6. Now repeat Steps 3 and 4 giving the ball a hard downward push. Observe, measure, and record bounce height.

CONCLUSIONS:

Compare your results. When did the ball bounce the highest? Can you explain why?

DON’T STOP NOW!

* Try shooting basketballs at different distances from the basket. How could the results of your experiment help you figure out how much force to use for each shot?

* On your way home from school, make a list of which laws of motion you see in action (e.g., on the school bus, while walking, skateboarding, etc.).