Water Balloon in the Jar

Water Balloon in the Jar

Water Balloon in the Jar
Expansion and Contraction

Students try (usually unsuccessfully) to push a water balloon into a jar. Using concepts of expansion and contraction, the teacher demonstrates how to easily get the balloon into the jar, and then poses the question, "What makes the water balloon go into the jar?" Use inquiry techniques to work on the question.

Advanced Preparation

Assemble all materials

Duplicate observation frames for students if desired

Obtain a glass jar for the demonstration. The opening should be about 5 cm, a larger opening works even better because a larger water balloon can be used, making a more dramatic demonstration.

Fill several of the large balloons with water. They should be larger than the opening of the jar, but should have plenty of elasticity left when filled.

Cut pieces of newsprint about 15 cm square (6" square).

If your classroom does not have a sink, arrange for a bucket to empty water into.

Try the demonstration for yourself!

Bring some bath towels for clean-up and to dry off students who may get wet.

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Materials

(for each student)

5 large balloons

1 glass jar, empty (top opening about 5 cm)

newsprint paper

matches

towels

plastic straws or other tube

water

sink or bucket

Optional:

liquid soap or other lubricant

Safety Notes

When students are attempting to push the water balloon into the jar, assign a student to hold the jar so that it is not accidentally pushed off of the table.

Heating the air within the jar should only be accomplished with a small piece of burning paper. Under no circumstances should the jar be held over a flame or placed on a hot plate. If heated in this manner, the jar will expand and contract unevenly and could shatter into glass shards!

Students will often suggest heating the jar as a data generating experiment. In this case the teacher should provide the data without heating the jar with the flame. Explain that the suggested activity is not safe, but would in theory provide similar results to dropping a burning paper into the jar.

Leading the Activity

Show the materials and ask for a few student volunteers to try to get the balloon into the jar. Have one student be assigned to hold the jar (as students push the water balloon in, the jar may move around on the table and could accidently fall and break).

If the students are unsuccessful, ask them to consider why the balloon will not go easily into the bottle, even though it is flexible enough to change its shape (the jar is already full of air, and the air is in the way).

If students are successful, ask them to discuss what made them successful (they may have pushed the balloon away from the edge of the opening allowing the air in the jar to escape).

Discuss ways of getting the balloon into the jar (a small hole near the bottom of the jar, for example, would allow the air to escape).

Perform the demonstration, encouraging students to make careful observations in sequence. Observation frames can be cut out and used to sequence observations. As the demonstration is repeated, students can rearrange and/or add observations missed the first time.

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Procedure

Accordion-fold a piece of newsprint (about 15 cm square) so it will fit into the jar.

Light one end of the folded newspaper and as soon as it is well-lit, drop it into the jar.

Immediately cover the opening of the jar with the water balloon, holding it by the knotted end. The balloon should "wiggle" or "bounce" as the heated air expands and escapes. The balloon acts as a one-way valve to let expanding air out, but as the air inside contracts, no air is allowed back in to take the place of the air which left. A partial vacuum is created which pulls the balloon into the jar. The lip of the jar may be lubricated with liquid soap, petroleum jelly, etc. if desired.

The balloon may be removed by grasping the knotted end and inserting a straw or other tube into the jar as you pull the balloon out. The tube allows air to enter the jar and fill the empty space which is created as the balloon is pulled out.

Use observation frames to sequence the observations of the activity.

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Water Balloon in the Jar
		Expansion and Contraction Students try (usually unsuccessfully) to push a water balloon into a jar. Using concepts of expansion and contraction, the teacher demonstrates how to easily get the balloon into the jar, and then poses the question, "What makes the water balloon go into the jar?" Use inquiry techniques to work on the question.

Advanced Preparation Assemble all materials Duplicate observation frames for students if desired Obtain a glass jar for the demonstration. The opening should be about 5 cm, a larger opening works even better because a larger water balloon can be used, making a more dramatic demonstration. Fill several of the large balloons with water. They should be larger than the opening of the jar, but should have plenty of elasticity left when filled. Cut pieces of newsprint about 15 cm square (6" square). If your classroom does not have a sink, arrange for a bucket to empty water into. Try the demonstration for yourself! Bring some bath towels for clean-up and to dry off students who may get wet. Back to top		Materials (for each student) 5 large balloons 1 glass jar, empty (top opening about 5 cm) newsprint paper matches towels plastic straws or other tube water sink or bucket Optional: liquid soap or other lubricant
Safety Notes When students are attempting to push the water balloon into the jar, assign a student to hold the jar so that it is not accidentally pushed off of the table. Heating the air within the jar should only be accomplished with a small piece of burning paper. Under no circumstances should the jar be held over a flame or placed on a hot plate. If heated in this manner, the jar will expand and contract unevenly and could shatter into glass shards! Students will often suggest heating the jar as a data generating experiment. In this case the teacher should provide the data without heating the jar with the flame. Explain that the suggested activity is not safe, but would in theory provide similar results to dropping a burning paper into the jar. Leading the Activity Show the materials and ask for a few student volunteers to try to get the balloon into the jar. Have one student be assigned to hold the jar (as students push the water balloon in, the jar may move around on the table and could accidently fall and break). If the students are unsuccessful, ask them to consider why the balloon will not go easily into the bottle, even though it is flexible enough to change its shape (the jar is already full of air, and the air is in the way). If students are successful, ask them to discuss what made them successful (they may have pushed the balloon away from the edge of the opening allowing the air in the jar to escape). Discuss ways of getting the balloon into the jar (a small hole near the bottom of the jar, for example, would allow the air to escape). Perform the demonstration, encouraging students to make careful observations in sequence. Observation frames can be cut out and used to sequence observations. As the demonstration is repeated, students can rearrange and/or add observations missed the first time. Back to top Procedure Accordion-fold a piece of newsprint (about 15 cm square) so it will fit into the jar. Light one end of the folded newspaper and as soon as it is well-lit, drop it into the jar. Immediately cover the opening of the jar with the water balloon, holding it by the knotted end. The balloon should "wiggle" or "bounce" as the heated air expands and escapes. The balloon acts as a one-way valve to let expanding air out, but as the air inside contracts, no air is allowed back in to take the place of the air which left. A partial vacuum is created which pulls the balloon into the jar. The lip of the jar may be lubricated with liquid soap, petroleum jelly, etc. if desired. The balloon may be removed by grasping the knotted end and inserting a straw or other tube into the jar as you pull the balloon out. The tube allows air to enter the jar and fill the empty space which is created as the balloon is pulled out. Use observation frames to sequence the observations of the activity. Back to top