Sat, Dec 13, 2008 - Page 13 News List

WEEKEND SCIENCE 週末科學版: Having a ball: experimenting with air pressure 彈球測氣壓

Welcome to Weekend Science! Every Saturday we’re going to guide you through some cool experiments that you can do at home. It’s a good idea for you to keep a record of what you do in a Science Journal. That way you can record what you learn, compare results and maybe use them to design new experiments! Remember to always ask a grown-up’s permission before trying out an experiment.


Portland Trail Blazers’ Rudy Fernandez, of Spain, bounces the ball off his knee during the NBA basketball team’s media day at the Rose Garden in Portland, Oregon, US on Sept. 29, 2008.


In many ball sports, there is a rule that specifies the air pressure of the ball. Pressure is usually measured in psi (pounds per square inch). According to the NBA, a regulation basketball should be “inflated to 7.5 to 5.8 pounds pressure.” But why is it necessary to make such a rule? Why can’t umpires and referees just decide how much air to put in the ball? The answer is to do with the bounce. By regulating the air pressure, the players can be sure that the ball will bounce in a similar way as it did in the last game, and the game before that.(John phillips, staff writer)

In today’s experiment you will learn more about the correlation between air pressure and bounciness.

What you will need: a basketball, an air pressure gauge, a pump, stepladders, chalk, a video camera, a tripod and a meter stick.

許多球類運動都會明訂球壓標準。壓力常用的測量單位為「psi」(每平方英吋所承受的磅數)。根據全美籃球協會(NBA)的規定,每顆標準籃球的「球壓應該要介於7.5到5.8 psi」。但為什麼一定要有這種規定呢?為什麼裁判和評審不能自行決定球要充多少氣呢?答案和彈力有關。藉由規範球壓,選手們就可以確定球的彈力會和前場比賽,還有上上場比賽時差不多。(翻譯:袁星塵)





Step 1: Find a wall that you can mark with chalk. The side of a building will work well.

Step 2: Using the meter stick, chalk and step ladders, mark 10cm intervals on the wall from one meter up to three meters.

Step 3: Using the tripod, position your video camera so that it can capture all the markings on the wall. Set the camera to record.

Step 4: Record the pressure of the ball and drop it from the top of the stepladders.

Step 5: Use the pump to increase the pressure by 0.5psi. Drop the ball from exactly the same position. Repeat at least five times, recording the pressure before each drop.


1. air pressure n.

氣壓(qi4 ya1)

2. correlation n.

關聯 (guan1 lian2)

3. gauge n.

測量儀器 (ce4 liang2 yi2 qi4)

4. tripod n.

三腳架 (san1 jiao3 jia4)

5. surface n.

表面 (biao3 mian4)

6. energy n.

能量 (neng2 liang4)








Record the results

Step 1: Your video camera should have captured the height of each bounce. Freeze the shot when the ball is at its highest and record it next to the corresponding air pressure.

Step 2: Put the results in a graph. You should notice a correlation between the air pressure and the height of the bounce.




Why it happened

The air molecules in the under-inflated ball are loosely packed. When the ball hits the ground, its surface stretches, and the energy is dissipated. In the heavily inflated ball, the air molecules are densely packed. When the ball hits the ground, the energy from the fall is stored and returned, projecting the ball upwards.



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