Buoyancy and Floating Lesson Plan

1. Pray. Read & discuss Matthew 14:22-33

2. Ask, "What makes things float?" Let a few children share their ideas. Divide children into groups of 3-4. Give each group a bowl of water and some objects. Give each child 1 of each item except the oranges. Only give 1 orange to each group. Ask the children to make a hypothesis by dividing the objects into what 2 groups, items that will float in water and items that will sink in water. After the groups have divided their items, have them each use some words to describe each of their piles. (For example, they might say "heavy" items will sink while "light" ones will float.) After the children have shared their descriptions, hold up a penny and an apple. Ask, "Which item will float?" Demonstrate that the apple floats in water and the penny sinks. Ask, "Which one weighs more?" If the apple weighs more than the penny, then why does it float? We'll explore that concept today. Allow children to now test out their 2 piles and see if they were correct about which items float and which sink.
YOU WILL NEED: 1 apple and per group of 3-4: 1 oranges/clementine, 1 container for water (like plastic shoe boxes), towels, & various items for children to test out such as a paper clip, toothpick, penny, bottle cap, marble, plastic bead, sponge piece, pencil, piece of aluminum foil, piece of paper, small balls, piece of Styrofoam, plastic spoon, wooden spoon, twig, etc.

3. After the children have tested the buoyancy of all their items, find out if all the groups came up with consistent results. ("Did the marble sink for everyone? How about the plastic beads? The aluminum foil?") If there are differences in their findings, ask the children to speculate why this could be. How could they explore this further? Did the difference have to do with different procedures? Ask, "Is there a way that you could change some of the sinkers into floaters or make the floaters into sinkers?" If no one has ideas, ask, "What would happen if you changed the shape of the aluminum foil? What happens if you peel the orange?" Try it! An unpeeled orange floats because its skin has pockets of air. Ducks and geese float for a similar reason. Their feathers contain tiny tubes filled with air. Sometimes young swimmers use air-filled water wings to stay afloat. When you removed this layer of air pockets (the peel) from the orange, it sinks a bit, just like what would happen if you removed water wings from some young swimmers. Assist children who need assistance in peeling the orange. After they see how an unpeeled orange sinks, let them divide it up and eat it. (Note: According to a book, the unpeeled orange was supposed to sink. It didn't. However, it didn't float as high as the unpeeled orange, so it would be best to compare a peeled and unpeeled orange in the water at the same time.)
YOU WILL NEED: napkins and hand sanitizer

4. Refer back to the words the children originally used to describe items that float or sink. Ask the children to look for commonalities among the items that float and those that sink. Which descriptive words would they change? Are there words they would add? Introduce vocabulary: objects that float can be described by a new word, "buoyant." Have everyone say the word, "buoyant." Ask, "What does it mean for an object to be buoyant?"

5. Read a book on buoyancy, Let's Try It Out in Water by Seymour Simon. (Note: This wasn't a great book, but we couldn't find another one that was better.) The Magic School Bus Ups and Downs by Joanna Cole is more appealing picture-wise, but it is VERY basic.

6. Let children pass around 4 identical boxes that have been filled with different materials. After everyone has held all the boxes ask them to compare them. Let students handle the boxes, but do not let them open the boxes. It would be a good idea to tape them shut, anyway, to prevent leaks. Then ask the children to compare the features of the four boxes. They should note that the boxes look identical. Tell them that another way of saying that the boxes are all the same size is to say their volumes are identical. Have the children say, "volume." They should also note that the boxes had different weights. Tell them that another way of saying that is to say they have different masses. Have the children say, "Mass." Once these two observations have been made, you can let the children know there is one word that includes both of those observations. That word is density. Have them say the word, "density." Density tells us how much material is packed into a given amount of space. It tells us how the masses of two different objects would compare if they both had the exact same volume. The dry cereal (or popped popcorn) is not very dense. The material in the box does not weigh very much, because there is a lot of air occupying the spaces between the cereal flakes (or between the popped corn kernels, which themselves contain a lot of air, too). The sand and rice grains are more dense; they can pack together more tightly in the box. Sand grains can pack very tightly together, and so the box containing them is the densest of all.
YOU WILL NEED: 4 identical containers (like macaroni & cheese boxes) each one filled with a different substance (like popcorn, rice, sand, and cereal) and taped closed

7. Ask the children how it could density can be quantified. Point out that we use meters or feet for describing length, degrees for describing temperature, and miles per hour for describing speed. What units should we use for describing density, if it is the amount of material that fits into a given volume? Remind them of the 2 words you had them say before. Mass (or weight) and volume are the two quantities needed. Density is defined as the amount of mass per volume of a substance. Per always means divide. They are already familiar with speed: to find the speed, they divide the miles traveled by the hours it took to travel them. This division results in the speed expressed as miles per hour. Have the children use rulers to measure the sides of the boxes. On a large sheet of paper write the 3 measurements and multiply them together to get the volume of the box. Weigh 2 boxes on a scale to determine their weight/mass. Write that on the paper. Now write the density of the boxes (including the units, oz./in3) on the board. Scientists really use grams and centimeters, so the measurement for density is really g/cm3. The heavier box should, of course, have a higher density.
YOU WILL NEED: 4 rulers, scale, writing utensil, & paper

8. Ask, "How do you think density relates to buoyancy, or the ability of an item to float?" Let children share their ideas. Pass around a golf ball and a ping-pong ball. They have similar volumes but one is much heavier, therefore, more dense. Which item do they think will float? Sink? Drop them both in a bowl of water and see if they were right.
YOU WILL NEED: 4 golf balls, 4 ping pong balls, & 4 containers of water

9. It's not always obvious which item is more dense. Pass out a can of Coke and a can of Diet Coke to each group. Ask the children if they both have the same volume. (Yes.) Do they have the same mass? The same density? Let's find out. Ask them to form a hypothesis: will both sink, both float, or one sink and which one? Have them place both cans in a container of water. (You can have the children in the group who didn't get to drip the balls in the water in 4c drop the cans in the water.) What happened? Based on what you just saw, which can of soda has more mass? (non-diet) How did you know that? (It sank.) The denser can must have more because you know they have the same volume. The regular Coke has more "stuff" in the same sized can, though. Can anyone guess what the difference might be. (It is the corn syrup in the regular Coke that makes it more dense than the diet Coke which contains artificial sweetener.) (Note: You need to use a large container of water for this demonstration as the smaller, shoe-box size containers of water weren't able to demonstrate this as much. The Diet Coke cans we used did not sink, but they did float lower than the cans of regular Coke when we used a large container of water like a medium size plastic storage bin.)
YOU WILL NEED: 4 cans of Coke, 4 cans of Diet Coke, and 4 large containers of water

10. Ask the children, "How does a boat or ship float carrying hundreds of pounds worth of cargo while that same cargo would sink to the bottom of the ocean if dumped overboard?" Let them share their ideas. Ask them who went swimming this summer. When you are in a pool and you stretch out your body, you will float. But if you wrap your arms around your legs and curl up into a ball, you will sink. It all has to do with how much water is pushing against you and a little scientific principle called buoyancy. When you stretch out flat more water pushes against you since your body is laid out flatter and has more surface area. Have the children say, "surface area." When you curl up into a ball, your body is more compact and less water is pushing against you. You have less surface area. Have the children show you how they can have their bodies take up the most surface area (by spreading out) and then the least surface area (by curling up tightly).

11. Give each group a container of water, and give each child a piece of modeling clay. Have the children roll the clay into a ball and place it in the water. What happens? Now have them take the same piece of clay and roll into a cylinder shape and place it in the water. What happens? Have them take the same piece of clay and fashion it into a flat-bottomed boat shape and then place it in the water. What happens? Ask, "Why did the first 2 shapes sink and the boat (ship) shape float?" Let children share their ideas. Explain that if the total area of the object that makes contact with the water is large enough, the object floats. The object must make room for its own volume by pushing aside, or displacing, an equivalent (or equal) volume of liquid. The object is exert¬ing a downward force on the water and the water is therefore exerting an upward force on the object. Of course the floating object's weight comes into play also. The solid body floats when it has displaced just enough water to equal its own original weight. This principle is called buoyancy. Have the children say, "buoyancy." The lump of clay pushed down on a small area of water, so it sunk. Why do items that are hollowed out seem to float best? The ship-shaped clay pushes down on a bigger area of water. The water can push up against more of the clay and it up so that the ship-shaped clay can float.
YOU WILL NEED: clay (do NOT use play-doh) & 4 containers of water (like plastic shoe boxes)

12. Let's consider the cargo in the ships or barges. Hand out pennies to everyone. Tell them to make a hypothesis: Will they sink or float? Have them drop the pennies in the water. Ask, "Is there a way you could use your clayboat to help the pennies float?" Let the children try. Ask, "What happens if you put all the pennies on only one side of your boat?" Try it. It will start to sink! A ship's captain has to be careful to place his/her cargo evenly on the ship. They usually start in the middle and work their way outward. What happens when you add all the pennies into one clay ship? Try it. You're increasing the mass without increasing the volume. Your ship is going to sink!
YOU WILL NEED: pennies

13. Ask children what they learned about buoyancy, density, and surface area/displacement. Tell them that we are going to apply what they learned to barge-building. We will have a contest to see who can build a boat hull that will hold the most mass while staying afloat. Children want to achieve the highest loading capacity. Give each child a 12" x 8" piece of aluminum foil. They can test their ship as many times as they would like before the final "contest" but they may not get a new piece of foil. If their boat tears, they will have to repair it. Moms should help the youngest children. Divide the children into 3 groups by approximate age (oldest, middle, & youngest). From each age group select the barge that can hold the most pennies.
YOU WILL NEED: pennies, aluminum foil, water, towels

14. Have the 3 "winners" show off their barge designs. Ask, "What can you say about your hull design? What is the equivalent 'boat' to your design? (Canoe, barge, speedboat, etc.) How did the placement of pennies affect the number the boat holds?" You can let them know that best designs are flat barges with small sides. The placement of pennies also makes a difference in the number held. The record for one sheet of 8" x 12" foil is around 280 pennies.

15. Ask, "Who can name a boat design that is mentioned in the Bible? Read Genesis 6:15-16. Ask the children, "When you were designing your aluminum foil ships, were you trying to design a fast-sailing ship? What was your main goal?" No, your goal was to have them hold the most cargo without sinking. That was God's goal when giving Noah the design for the ark. The dimensions were at least 135 meters long (300 cubits), 22.5 meters wide (50 cubits), and 13.5 meters high (30 cubits). That's 450 feet long, 75 feet wide, and 45 feet high! We'll draw a small scale model of the ark. Give each child a piece of paper, a crayon/writing utensil, and a ruler. Have them measure 30"x5"x3." If desired, have children used tape and scissors to make a 3D model of the ark. This is a tiny scale model of the ark. Ask, "Does it look like the ark you usually see in children's books? What shape was it really?" (No. A rectangular box.)
YOU WILL NEED: Bible, paper, writing utensils, tape, scissors, & rulers

16. (If you are not limited by time) Now we're going to see how big it was in real life. Take everyone outside. Walk 450 feet (about 450 steps). Have everyone go together and count out loud together. Place a stick marker there. Then walk 75 feet. That's how wide it was. It was almost that tall. God protected Noah and his family and the animals by designing the perfectly-shaped ship for keeping them afloat amidst the rains.

17. Review what we learned today.

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