Background:

Basketball is a game played by two teams with a ball and the objective is to put the ball through one of two hoops placed at opposite sides of the court(Basketball Basics). Basketball was first invented in 1891 by James Naismith, and was played with peach baskets for hoops and a soccer ball. The NBA was founded in 1949 but the modern style of play wasn’t adopted until 1976 (Sports Know How).

        The basketball itself is a sphere with a circumference of 29.5 inches and consists of an inner rubber bladder that is covered with either leather, rubber, or a synthetic substance. The purpose of a basketball is to be bounced, or “dribbled”, down a court and thrown into a hoop, so the ball has to be able to bounce fairly easily and have grip to be able to be thrown accurately. If the ball isn’t pumped to the required psi then its performance won’t be up to standards, either bouncing too little, or too much.

Elasticity is a term used for the property of a solid object to return to its original shape and size after the forces that deformed it are no longer acting on it (Elert). Things like springs, rubber balls, and rubber bands all have elasticity because they all revert back to their original shape after forces deform them. This means that for a ball if it is bounced then the force isn’t gone after it’s impact with the ground, its elasticity allows it to bounce. As a ball is dropped its velocity is downward with respect to gravity. As it collides with the ground the ball is compressed due to the impact, and as it snaps back to its original shape it pushes against the ground (Normani). If the force of the ball pushing against the ground is greater than the ball’s weight, then it will bounce back up to a certain height, always lower than the original if dropped, depending on how much force the push back gave it (Normani). It will repeat this process as gravity pulls it back towards the ground until the weight of the ball is too much for it to bounce back up.

Statement of the problem: The purpose of this investigation is to determine the effect psi has on the bounce/rebound height of a basketball.

Hypothesis: We believe that the bounce height of the basketball will increase as the psi inside the ball increases.  This will most likely occur because the increase in psi will increase the amount of air molecules in the ball, which cause it to become more rigid, and thus allow it to “snap” back with more force after it hits the ground.  The controlled variables include, but are not limited to: drop height of 6 feet, basketball, temperature, and ground surface.

Working Setup/Data

Method:

In order to collect the data for our experiment we will first gather all the materials necessary.  We will then put up the ladder and climb up to a height of 6 feet.  Next we will drop the ball and measure the maximum height after the first bounce by using a slow motion camera.  Using the camera will allow us to see, with relative certainty, when the ball has stopped its upward ascent and will allow us to find it maximum height after one bounce.  We will repeat this process starting at a psi of 5 lbs per square inch and increasing the pressure each by 0.5 psi.  We will test the ball at 10 different pressures with three trials each.  After 3 trials of the first pressure, we will then inflate the basketball by 0.5 psi and use the pressure gauge to check.  We will do this every time before we test the next pressure.  Continue the process until all data has been collected.

Materials:

Basketball, psi gauge, ball pump, tape measure, ladder, camera.

Diagram:

Results

Data Table:

Summary of results: After collecting all the data, we noticed that as the psi inside the basketball increased, the bounce height of the ball increased at a near-constant rate. Furthermore, the results agreed with our hypothesis.

Graph:

Data: Excel .:. Text

Conclusion

        The results showed that the pressure did affect the bounce of the basketball when it was dropped from six feet. As the psi increased, the ball bounced higher each time giving a total difference of 11 inches from the first trial to the last trial. Our hypothesis predicted that the increase in psi would give a higher bounce and it was correct. For the range of the pressures that we tested we only had growth in bounce height. This meant that the ball was still being compressed each time and rebounding with greater force each time.

The increase in psi increased the bounce height because it allowed the ball to become more rigid as the psi increased. This caused the ball to snap back to its original shape with more force once it hit the ground because the added pressure resisted the ball’s change in shape more each time pressure was added. This trend would be expected to continue until a certain point where the pressure would be too great for the ball to bounce as high as the previous trial because it would be too rigid to compress as much.

        Main sources of error were probably in our data collection. We used an iPhone with a slow motion camera to record the bounce and a measuring tape on the wall and we just eyeballed where it bounced back up to from looking at the film. Our measurements could have been more precise. There was also slight error in the pressure gauge because it couldn’t have been perfectly precise for each trial. There was also a minute leak of air as the needle was removed from the ball after inflation, but there isn’t a great way to fix that unless we improved upon the manufacturer’s seal.  Another possible error in the data collection was that the drop height wasn’t always exactly constant.  While the general height that the ball was dropped at was six feet, it was impossible for us to drop the ball at the exact same height each time.

        To improve on our procedure we would use a higher drop height to emphasize change in the data and have a camera mounted sturdily with slow motion to give us more precise measurements. We would also test more pressure variations by doing more trials starting at zero and going beyond the ball’s maximum psi. We would have done this but we didn’t have an old ball to use. It would have been much better to go beyond the ball’s maximum psi to see if there was a point where the increase in bounce height stopped, and started to decrease. This would be expected because eventually it would become much too rigid to have the same bounce as before.

Related Websites