My kid needs to do a science project for elementary school, what are some cheap but fun projects to do?
There are many cheap and fun science projects that elementary school kids can do! Here are a few ideas:

1. Make a homemade lava lamp: Fill a clear plastic bottle with water and vegetable oil, add a few drops of food coloring, and then drop in an Alka-Seltzer tablet. The reaction will cause bubbles to rise and fall like a lava lamp.
2. Build a bridge out of spaghetti: Using only uncooked spaghetti and white glue, challenge your child to build a bridge that can support the weight of a small toy or object.
3. Make a simple circuit: Using a battery, a lightbulb, and some wire, have your child create a simple circuit to light up the bulb.
4. Grow crystals: Mix water, borax, and food coloring to create a solution that will grow crystals when left undisturbed for a few days.
5. Make a homemade volcano: Using baking soda, vinegar, and red food coloring, create a chemical reaction that mimics a volcanic eruption.
6. Build a birdhouse: Using wood scraps and a few simple tools, have your child build a birdhouse to attract birds to your yard.
7. Create a solar oven: Using a pizza box, aluminum foil, and plastic wrap, create a solar oven that can cook s'mores or other small snacks.
8. Explore magnets: Using magnets and a variety of objects, have your child experiment with magnetism to see what objects are attracted to magnets and which ones are not.

These are just a few ideas to get you started! There are many more cheap and fun science projects that your child can do with household items and a little creativity.
Can you elaborate on point 7? Seems interesting!
Here's a solar oven project from NASA's science activities for children. A solar oven is a box that traps some of the Sun’s energy to make the air inside the box hotter than the air outside the box. In other words, the solar oven is like a super greenhouse. However, for this to work, you will need to have a sunny day when the temperature is at least 85 °F/29 °C.

## Materials
  1. Cardboard box with attached lid. Lid should have flaps so that the box can be closed tightly. Box should be at least 3 inches deep and big enough to set a pie tin inside.
  2. Aluminum foil
  3. Clear plastic wrap
  4. Glue stick
  5. Tape (transparent tape, duct tape, masking tape, or whatever you have)
  6. Stick (about 1 foot long) to prop open reflector flap. (Use a skewer, knitting needle, ruler, or whatever you have.)
  7. Ruler or straight-edge
  8. Box cutter or Xacto knife (with adult help, please!)

## How to make the solar oven
  - Using the straight edge as a guide, cut a three-sided flap out of the top of the box, leaving at least a 1-inch border around the three sides.
    - Please have an adult help or supervise while handling the the box cutter or Xacto knife.
  - Cover the bottom (inside) of the flap with aluminum foil, spreading a coat of glue from the glue stick onto the cardboard first and making the foil as smooth as possible.
    - The smoother you can make your foil, the better your solar oven will work.
  - Tape two layers of plastic wrap across the opening you cut in the lid—one layer on the top and one layer on the bottom side of the lid.
  - Test the stick you will use to prop the lid up. You may have to use tape or figure another way to make the stick stay put.

## Put the oven to work
  - Set the oven in the direct Sun on a sunny day when the outdoor temperature is at least 85 degrees Fahrenheit (29 degrees Celsius).
  - Prop the flap open to reflect the light into the box. You will probably have to tape the prop in place. Preheat the oven for at least 30 minutes.
 
## S'more Ingredients
  - Graham crackers
  - Large marshmallows
  - Plain chocolate bars (thin)
  - Aluminum pie pan
  - Napkins

## Cooking Instructions
It's important to note that making S'mores in a solar oven requires changing the cooking process slightly.
  - Break graham crackers in half to make squares. 
  - Place four squares in the pie pan, then place a marshmallow on each.
  - Place the pan in the preheated solar oven.
  - Close the oven lid (the part with the plastic wrap on it) tightly, and prop up the flap to reflect the sunlight into the box.

Depending on how hot the day is, and how directly the sunlight shines on the oven, the marshmallows will take 30 to 60 minutes to get squishy when you poke them.

  - Open the oven lid and place a piece of chocolate on top of each marshmallow.
  - Place another graham cracker square on top of the chocolate and press down gently to squash the marshmallow.
  - Close the lid of the solar oven and let the Sun heat it up for a few minutes more to melt the chocolate a bit.
   - Enjoy your S'mores!