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# Hands-On Science

physics

## Design a Submarine

Become an engineer and design a submarine that moves in the water like a real submarine.

## Materials

• Small container with a lid (pill container, film canister, plastic bottle, etc.)
• Variety of small, heavy objects (coins, marbles, screws, washers, etc.)
• Variety of small, light objects (paper clips, fabric pieces, cork, beads, etc.)
• Rubber bands or string
• Large container or tub
• Water
• Paper
• Pen

## Directions

1. Fill the container with water and set all the small objects and rubber bands or string nearby. The small container is your submarine.
2. Figure out how to make it float on top of the water, using any of the objects. Write down what you did and the materials you used. How many different ways can you find to make it float?
3. Now figure out how to make your submarine sink to the bottom of the container, using any of the objects. Write down what you did and the materials you used. How many different ways can you find to make it sink?
4. Figure out how to make your submarine hover in the middle of the water, using any of the objects. That means no part of it can be touching the top of the water, and no part of it can be touching the bottom of the container. Write down what you did and the materials you used. How many different ways can you find to make it hover?

## What's happening?

Density is defined as weight per volume. The formula is Density = Mass/Volume. In the submarine, the volume stays constant. The density changes by adding or taking away the different objects.

When two or more forces act on an object, the result is the cumulative effect of those forces. The buoyant force is the net upward force (or uplift) exerted by a fluid on a submerged object. Gravity counters this force by pulling down on an object while the buoyant pushes the object up. If an object’s density is more than that of the liquid, it will sink (force of gravity is greater than the buoyant force). If an object’s density is less than that of the liquid, then it will float (force of gravity is less than the buoyant force). If an object’s density is the same as that of the liquid, it will hover (force of gravity is equal to the buoyant force).