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Design Challenge: A Cool Pad for a Bike Helmet

Grade 7 physical science: use cup tests and time readings for three helmet cool pads to judge a design that absorbs thermal energy as a salt dissolves.

Grade 7ScienceInteractive · Printable

Aligned toMS-PS1-6

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What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
12 questions
Classroom-ready

Details

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 use test data to explain how a dissolving salt absorbs thermal energy from its surroundings.
Students compare prototypes against criteria and explain how a sleeve and crystal size change the energy transfer.
Students plan a fair next test to improve a device.

How to use

Read the criteria in paragraph 2 together and have students restate each one before they open Table 2; the last question works well as a short written argument or a pair discussion.

Curriculum

NGSS standard covered

MS-PS1-6

Design and test a device that releases or absorbs thermal energy through a chemical process, such as a hand warmer.

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Name Date

Design Challenge: A Cool Pad for a Bike Helmet

Test how much salt to use and compare three prototypes against the criteria.

Test 1: How much salt?

Read the passage and study Table 1. Then answer the questions.

Keeping Cool Under a Helmet

1Every July, the bike safety club at Pinehollow Middle School runs a bike rodeo in the school parking lot. Younger riders practice signaling, braking and steering around cones while club members coach them. On hot afternoons the blacktop can feel like an oven, and a helmet traps warm air around a rider's head. Riders keep their helmets on for the whole course, so club members Dario Benedetti and Simone Achterberg decided to design a flat cool pad that slides into the padding at the front of a helmet and turns cold only when it is squeezed.

2The club's adviser, Ms. Harriet Nakashima, explained that some chemical processes absorb thermal energy from their surroundings. Ammonium chloride is a white salt that does this as it dissolves in water. The club agreed on four criteria. First, the skin side of the pad must be at or below 20 °C at the 5-minute reading. Second, it must never read below 10 °C, because a very cold pack held on skin can hurt it. Third, it must stay at or below 20 °C at every reading from 5 minutes through 25 minutes. Fourth, the whole pad must have a mass of 160 g or less, so it does not tug the helmet forward.

3Ms. Nakashima measured out every amount of ammonium chloride, and everyone wore goggles and gloves. In Test 1, she stirred fine ammonium chloride powder into 100 mL of 24 °C water in a foam cup with a lid. Only the mass of the powder changed from cup to cup. The club recorded the lowest temperature of the water and whether any solid was left at the bottom after five minutes of stirring (Table 1).

4For Test 2, the club built three pads. Each one held 100 mL of 24 °C water in a sealed outer bag and 30 g of ammonium chloride in a thin inner pouch that breaks when the pad is squeezed. Pad A used fine powder in a plain plastic bag. Pad B used the same powder, but its bag was sewn into a thin cotton sleeve. Pad C had the same cotton sleeve but held coarse crystals about the size of rice grains instead of fine powder.

5To stand in for a rider's forehead, an adult filled a bottle with 35 °C water and wrapped it in a towel. Each pad lay on the bottle with a temperature probe taped to its skin side, and the club read the probe at the times in Table 2. For the mass criterion, Simone noted that 100 mL of water has a mass of about 100 g and that the bag, the inner pouch and the sleeve together have a mass of 12 g.