Worksheet

Leather or Synthetic? Soccer Balls for a Rainy Season

Grade 7 physical science: trace leather, PU, PVC and rubber ball parts to natural resources, analyze a soak and air test, and weigh effects of synthetics.

Grade 7ScienceInteractive · Printable

Aligned toMS-PS1-3

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1 NGSS standard
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10 questions
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Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Matching, Circle the answer, Short answer

About this worksheet

What students practice

Students explain how PU, PVC and butyl rubber are made from natural resources by chemical reactions.
Students analyze soak and air-pressure data to compare natural and synthetic ball materials.
Students weigh the benefits and costs of synthetic sports materials for society and the environment.

How to use

Read paragraphs 1–4 together and list each ball part with the resource it comes from. Students can then analyze both tables on their own; the last question works as a written assessment.

Curriculum

NGSS standard covered

MS-PS1-3

Explain how synthetic materials, such as plastics and medicines, are made from natural resources and affect society.

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Name Date

Leather or Synthetic? Soccer Balls for a Rainy Season

Trace ball materials to natural resources and weigh their effects on society.

What a soccer ball is made of

Read the passage. Then answer the questions.

Heavy Balls on Rainy Saturdays

1The Lakeside youth soccer league plays every Saturday from September to November, rain or shine. Seventh graders Oskar Halloran and Adwoa Boateng volunteer in the league's equipment shed with Coach Imelda Barrientos. Last fall, many players complained that on rainy days some of the old match balls felt heavy and stung when they were kicked. Coach Barrientos asked Oskar and Adwoa to find out which kind of ball the league should buy next.

2A soccer ball has two main parts: an outer cover and an inner bladder that holds the air. About a hundred years ago, most balls had a leather cover, made from cowhide, stitched around a bladder of natural rubber. Natural rubber comes from latex, a milky sap collected from rubber trees. Today, most match balls have a cover of polyurethane (PU), a synthetic leather, or of polyvinyl chloride (PVC). Many bladders are now made of butyl rubber, a synthetic rubber.

3Synthetic materials are made when substances taken from natural resources react to form new substances. To make PU, small molecules made from crude oil or natural gas react and link into long chains. PVC is made from natural gas or crude oil and from ordinary salt, which supplies its chlorine atoms. Butyl rubber is made from small molecules that come from crude oil or natural gas.

4Synthetic balls have changed the game in many places. They often cost less than leather balls, so schools and leagues around the world can afford more of them, and they keep about the same weight in the rain. Synthetic materials also have costs. Crude oil and natural gas cannot be replaced once they are used up. Worn-out synthetic balls usually end up in landfills, where the plastics break down very slowly. Making and burning PVC must be done with care, because it can release harmful gases.

5For their test, Oskar and Adwoa took one ball of each kind from the shed. They pumped each ball to the same pressure and weighed it dry. They soaked each ball in a tub of water for 30 minutes, wiped it with the same towel and weighed it again. After the balls dried, the students pumped them to the same pressure once more, left them on a shelf for 7 days and measured how much of the pressure was left (Table 1).

Use paragraphs 2 and 3. Match each ball part to the natural resource it is made from.

Leather cover
Natural rubber bladder
PVC cover
Butyl rubber bladder

A. Salt plus crude oil or natural gas
B. Crude oil or natural gas alone
C. Latex from rubber trees
D. Cowhide

Adwoa says, "PVC should count as a natural material, because salt is dug out of the ground." Which reply fits paragraph 3 best?

A. PVC is synthetic, because it is pressed into a ball shape in a factory.
B. PVC is natural, because the salt is still salt inside the finished ball cover.
C. PVC is natural, because salt and natural gas are both found in nature.
D. PVC is synthetic, because substances from salt and natural gas react to form a new substance.

The soak and air test

Use paragraph 5 and Table 1 to answer the questions.

Table 1. One Ball of Each Kind (air pressure left after 7 days)
Ball	Cover	Bladder	Dry mass (g)	Mass after soak (g)	Air pressure left (%)
1	Leather	Natural rubber	430	505	70
2	PU	Butyl rubber	425	431	95
3	PVC	Butyl rubber	420	423	96
4	PU	Natural rubber	425	432	72

Use Table 1.

During the soak, Ball 1 gained g of water, and Ball 3 gained g of water.

Use Table 1. Round to the nearest whole percent.

The water Ball 1 gained was about % of its dry mass.

Which two balls best show that the leather cover, and not the bladder, made a ball soak up more water?

A. Balls 1 and 2, because they gained the most and the least water
B. Balls 1 and 4, because they have the same bladder but different covers
C. Balls 2 and 3, because they have the same bladder but different covers
D. Balls 2 and 4, because they have the same cover but different bladders

Which conclusion about holding air does Table 1 support best?

A. The PVC ball lost the most air because its cover was the lightest.
B. The PU covers kept in about as much air as the PVC cover, whatever the bladder.
C. The butyl rubber bladders kept more air in than the natural rubber ones.
D. The ball that soaked up the most water kept the most air.

Oskar and Adwoa tested only one ball of each kind. Which change would make their conclusions more trustworthy?

A. Test several balls of each kind and average the results
B. Pump each ball to a different pressure before the soak
C. Wipe each ball with a different towel after the soak
D. Soak the leather ball longer than the other balls

Weighing the choices

Use paragraph 4, Table 1 and Table 2 to answer the questions.

Table 2. Supplier Information for Each Kind of Ball
Ball	Price per ball	Lasts about
1 (leather, natural rubber)	$60	2 seasons
2 (PU, butyl rubber)	$30	3 seasons
3 (PVC, butyl rubber)	$12	1 season
4 (PU, natural rubber)	$28	3 seasons

The league needs 40 balls. It buys a full new set of 40 balls each time a set wears out. Plan for 6 seasons.

Buying Ball 3 for 6 seasons would cost $ . Buying Ball 2 for 6 seasons would cost $ .

Underline each statement that describes an effect of synthetic balls on society or the environment.

Leagues around the world can afford more balls.Ball 3 gained 3 g of water in the soak test.Worn-out balls add plastic to landfills, where it breaks down slowly.Ball 2 kept 95% of its air pressure for 7 days.Rainy-day matches can be played with balls that stay about the same weight.

10.

Which ball should the league buy for its rainy fall Saturdays? Write a claim. Use data from Table 1 and Table 2 as evidence. In your reasoning, name the natural resources your ball is made from and describe one benefit and one cost of that choice for society or the environment.