Worksheet

From Oil to Foam: Choosing Liners for Free Bike Helmets

Grade 7 physical science: trace helmet foams to crude oil, analyze a two-hit drop test and weigh the benefits and costs of synthetic foam for a city helmet program.

Grade 7ScienceInteractive · Printable

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

About this worksheet

What students practice

Students explain how synthetic foams such as EPS are made from crude oil or natural gas by chemical reactions.
Students analyze drop-test data to compare synthetic and natural padding materials.
Students weigh the benefits and costs of a synthetic material for society using data.

How to use

Read the passage together and ask students to point to the step where a new substance forms. Students can then work through the drop test and the budget question in pairs.

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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From Oil to Foam: Choosing Liners for Free Bike Helmets

Trace helmet foams to natural resources, analyze a drop test and weigh the effects on society.

What a helmet is made of

Read the passage. Then answer the questions.

Helmets for Ride Safe Day

1Every May, the bike-safety club at Juniper Hollow Middle School helps the city run Ride Safe Day, when children get free helmets and a short riding lesson. While unpacking boxes of helmets, club members Nayeli Cruz and Lior Ben-David noticed that every helmet had the same three main parts. They asked their science teacher, Mr. Hamid Sadeghi, what each part is made of and where it comes from.

2The thick inner liner is expanded polystyrene, or EPS, a foam made of tiny beads. Making it starts with crude oil or natural gas, natural resources pumped from underground. At a chemical plant, small molecules taken from these resources react and link into long chains, forming a new substance: polystyrene. The polystyrene is made into small, hard beads. Steam puffs the beads up to many times their size, and then they are packed into a helmet-shaped mold and steamed again so that they stick together. In a crash, the foam crushes and spreads out the force of the hit. Crushed EPS does not spring back, and even small knocks can leave dents.

3The thin, hard outer shell is polycarbonate, a plastic made from crude oil by other chemical reactions. The straps are nylon, which also starts as crude oil or natural gas. Some newer helmets use a different foam called expanded polypropylene, or EPP. It is made from natural gas or crude oil in a similar way, but its beads bend and spring back after a hit.

4Before foam liners became common in the 1970s and 1980s, many bike racers wore helmets made of padded leather strips, which gave little protection in a hard fall. Today, studies have found that wearing a helmet greatly lowers the chance of a serious head injury in a crash. Foam helmets are light and cheap enough that cities can give them away. But the oil and gas used to make them cannot be replaced, few recycling centers accept old foam, and a liner thrown away can last for hundreds of years in a landfill.

5Nayeli and Lior wondered whether a natural material could protect as well as the synthetic foams. Mr. Sadeghi cut square pads, all the same size and 3 cm thick, from four materials. For each pad, he dropped a 1 kg steel weight from a height of 25 cm onto the pad, which sat on a force sensor. He then dropped it a second time onto the same spot. The sensor recorded the peak (highest) force of each hit. A lower peak force means the pad spread the hit out better. He tested three pads of each material and averaged the results.

Lior says, “EPS is a natural material, because crude oil is found in nature.” Which reply fits paragraph 2 best?

A. EPS is natural, because its beads are shaped and stuck together in a mold.
B. Crude oil is a synthetic material, because machines pump it up from deep underground.
C. Crude oil is a natural resource, but its molecules react to form a new substance.
D. EPS is natural, because the steam that puffs up the beads is plain water.

Use paragraphs 2 and 3. Sort each step in making a helmet.

Small molecules from natural gas link into long polystyrene chains.Steam puffs hard polystyrene beads up to many times their size.Puffed beads are packed into a mold and stuck together into a liner.Molecules from crude oil react to form polycarbonate for the shell.Nylon thread is woven into flat straps.

A new substance forms	Same substance, new size or shape

Use paragraph 4. Which effect of foam helmets on society is best supported by the passage?

A. Helmets became cheap enough for cities to give away, and riders who wear them have fewer serious head injuries.
B. Old foam liners break down within a few years in landfills, so they create little lasting waste for cities.
C. Foam helmets made bike crashes happen less often, because riders became more careful once they wore them.
D. Leather helmets were banned in the 1970s, and racers had to switch to foam helmets made from crude oil.

The two-hit drop test

Use paragraph 5, the bar graph and Table 1. The club's rule: a pad passes a hit if the peak force is less than 800 N.

Table 1. The Pads (average of 3 pads each)
Pad material	Made from	Pad mass (g)	Peak force, 2nd hit (N)
EPS foam	Crude oil or natural gas	20	950
EPP foam	Crude oil or natural gas	24	500
Cork	Bark of cork oak trees	66	650
Cotton batting	Cotton plants	8	1100

The peak force on the EPS pad was N higher on the second hit than on the first hit.

Why did the EPS pad do so much worse on the second hit than on the first?

A. The first hit warmed the foam, and warm foam spreads a hit out less.
B. The first hit crushed the foam, and it did not spring back for the second hit.
C. The first hit changed the polystyrene back into crude oil, which is a liquid.
D. The steel weight fell faster on the second drop, so it hit the already-tested pad harder.

Use the club's rule. Sort each pad by its results.

EPS foamCorkCotton battingEPP foam

Passed both hits	Passed the first hit only	Passed neither hit

Round to the nearest tenth. The cork pad has about times the mass of the EPS pad.

Which statement is best supported by the bar graph and Table 1?

A. Cotton batting gave the lowest peak force, because it was the lightest pad.
B. The heavier a pad was, the lower its peak force was on the first hit.
C. The pads made from plants gave the lowest peak forces on the first hit.
D. The two foams made from oil or gas beat both plant pads on the first hit.

Why did Mr. Sadeghi use the same 1 kg weight, the same 25 cm drop and pads of the same size for every test?

A. So that the pad material was the one thing that changed
B. So that each material would pass at least one of the hits
C. So that the cork pad would weigh the same as the EPS pad
D. So that the second hit would be weaker than the first hit

Weighing the effects

Use the passage, both data displays and Table 2.

Table 2. Helmet Choices for Ride Safe Day
Liner	Price per helmet	After small knocks	City drop-off takes it?
EPS foam	$12	Dents stay	No
EPP foam	$24	Springs back	Yes

10.

The city has $3,600 to spend on helmets. It can buy EPS helmets or EPP helmets.

11.

Sort each statement about EPS helmets.

Cities can afford to give helmets to many children.Old liners take up landfill space for a very long time.A 3 cm EPS pad had a mass of about 20 g.Riders who wear them are less likely to get a serious head injury.Making the foam uses up oil or gas that cannot be replaced.

Benefit to society	Cost to society or the environment	A test result, not an effect on society

12.

Nayeli wants the city to buy 300 EPS helmets. Lior wants 150 EPP helmets. Which should the city buy with its $3,600? Write a claim. Use data from Table 1 and Table 2 as evidence, explain what natural resource your choice is made from and how it becomes a synthetic material, and name one cost of your choice to society or the environment.