real science for today's homeschooler

Learning about Buoyancy in the Pool

Learning about Buoyancy in the Pool

Buoyancy seems like a simple concept, but to fully understand it on a scientific level can be a challenge for students. Introduce the concept to your younger elementary kids in a fun way while playing in the pool this summer!

Buoyancy is based on Archimedes’ Principle that states, “Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.” Very confusing language for kids! Here’s how to explain Archimedes in their language . . .

When you get in the pool, your body shoves some water out of the way to make room for you. Let’s say you could collect all the water your body moved out of the way and weigh it. Now, pretend that you lie down on the ground and have someone put all that water on top of you. You would feel the water pushing down on your body, right? That push you feel is a force. So, when you get in the swimming pool, the water you move out of the way starts pushing back. But instead of it pushing down on you, it pushes up trying to push you back out of the water. That force of the water trying to push you back out of the pool is called buoyancy!

Relate Archimedes’ Principle to what your child “feels” while in the pool. You feel lighter in water than you do out of the water because the water is actually pushing up on you . . . holding you up a bit!

If your child is able to understand the basics of Archimedes’ Principle, go a step further with the concept. If the weight of the water displaced is more than the weight of the object, the object will float. If the weight of the water displaced is less than the weight of the object, the object will sink. Ask them to explain why they sink in the water (when they don’t swim), but float when they lay on a float.

Finally, if your child swims well enough to “dive” for objects underwater, introduce a challenge. It’s them against the water! When they try to go underwater to get a object at the bottom of the pool, the water is trying to push them back up. The challenge? Who is stronger, you or the water? 🙂

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Understanding and Measuring Friction

Understanding and Measuring Friction

For elementary children, the topic of “opposing forces” can be hard to understand. Friction is an opposing force that children can “feel.” Here’s a lab on measuring and comparing friction that’s appropriate for older elementary children. You will need one piece of “science equipment” to get the most out of the lab . . . a spring scale. A spring scale with small increments will be easier for elementary children to use.

Here’s what to do:

1. Find an object that can be easily hooked onto the spring scale, that is fairly heavy (but will still read when hung from the spring scale), and preferably with a large, flat surface. A heavy block of wood with a cup hook works very well.

2. Have your child hook the object onto the spring scale and drag it across the smoothest possible surface you can find. While dragging the object slowly, have your child read and record the amount of force they are using to move the object. (Newtons is a measure of force, so the part of the scale marked as “N” is actually a measure of force.)

3. Next, have your child hunt for 5 different surface with as many different textures as possible. The surfaces must be large enough to drag the object across, just as was done in step 2.

4. Ask the child to predict what will happen when they drag the object across the different textured surfaces. They will most likely come to the conclusion that some surfaces will be harder to pull across than others. Ask them to come up with an explanation for WHY this is true.

5. Introduce the topic of “friction” by explaining that friction is a force that acts in the opposite direction from the force you apply to move an object. When they drag their object one way, the surface tries to pull it the opposite way!

6. Now, have your child predict which of their selected surfaces will pull more than others. Have them rang the surfaces in order from least friction to more friction.

7. Finally, it’s time to test their predictions. Have your child drag the object in the same way across each of the different surfaces. As they are slowly dragging the object, they should read and record the force they must use to pull the object.

8. Subtract the force needed to pull the object on the smooth surface from the force needed to pull it on each of the textured surfaces. This is a measure of how much more force the textured surface was putting on the object. The larger the number, the more friction force was applied by the surface.

To put it all together, remind your child that a force is just a push or a pull. So, when they put a force on the object in one direction, the surface will put a force on the object in the opposite direction. The more force applied by the surface, the harder they have to pull to get the object to move.

As an extension, relate this topic to the practical chore of moving a heavy object. Have them brainstorm ways that can be used to make sliding a heavy object easier.

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