Posts Tagged ‘physics’

More Backyard Science- Tablecloth Trick

July 30, 2009

This is a fun experiment to try outside, on the grass, where your kids can spill as much water as they want to.   All you need is a table, a sturdy glass that won’t break if it falls on the grass, a slippery tablecloth and water.


We used easel paper as our tablecloth, but your kids could try a plastic tablecloth or even a cloth one that doesn’t have a heavy seam on the edge.  The more slippery the tablecloth, the better it will work. You’ll also need a fairy heavy glass that is not too tippy.  I used a bar glass and it worked pretty well.  I’d also recommend bringing out a pitcher of water for refilling the glass and a towel.

Have your child put the paper or tablecloth near the edge of the table (see photo above.)  Place the glass of water on the tablecloth.  I wouldn’t recommend filling it to the top.


This part is important!  Your child must pull the tablecloth straight down, along the edge of the table, very fast.  If they pull it out, toward them, or pull it too slowly, it won’t work.  If they do it correctly (and it may take a few attempts), the water will slosh a little, but the cup will remain on the table, full of water.  We spilled a lot, but had a great time.  All of the older kids involved were able to do it successfully by themselves, but I had to help my three year old a little.

The law of inertia says that objects don’t want to change how fast they’re moving (or not moving, in the case of our glass.)  They heavier something is, the more inertia it has.  In our experiment, the heavy glass of water is standing still and doesn’t want to speed up.  Since the tablecloth is moving under the glass very quickly, the heavy glass slips on it and doesn’t move very far.   It seems like magic, but it’s just physics.

Have fun!

Throwing Eggs-Backyard Physics

June 21, 2009


Next to the kitchen table, my back yard (or front yard) is my favorite science laboratory.  It has the added bonus of being easy to clean up.  For this fun, messy experiment, a hose and a few paper towels did the trick. 

My dad, who is a physicist, told me about this great demonstration that teaches kids a little bit about motion and force while letting them do something that they are rarely, if ever, allowed to do- throw eggs!  All you need is a sheet, some clothespins or string, raw eggs, and some paper.  You could use newspaper or easel paper.  It is just to make cleaning up easier.  I also used a portable table turned on its side as a wall, but you could just use a wall and have your child hose it off when you are finished.

Hang the sheet up from a tree, if you have one.  If you don’t have a tree, you could hang it from anything else, or have two tall children or adults hold it.  Then have two children hold the bottom of the sheet up, or tie it to chairs  so it makes a J shape when you view it from the side.  The idea is to keep the eggs from hitting the ground and breaking. 


Have your child throw a raw egg at the sheet as hard as they can.  It won’t break because the sheet slows the egg down.  The law of motion says that the faster you change speed, the greater the force.  When you change the speed of the egg slowly, like the sheet does, it lessens the force of the egg stopping and the egg remains intact.

Now, put some paper on a wall (or table like we did.)  Have your child throw the egg at the wall.  They will see what happens when something stops fast.  Once again, the law of motion rules.  When you change the speed of the egg quickly, it stops with a lot of force.  SPLAT.  My kids loved this part.  I had to stop them from using all my eggs. 


Tell them that this is one reason they put airbags in cars.  If a car is moving and hits something, causing it to stop very quickly, the airbag act like the sheet, slowing the person in the car down and greatly reducing the amount of force they might hit the dashboard with. 

Have your child record their results in their science notebook, if they want to.  They can write or draw what they did, write the word force and record how many eggs they threw and which ones broke. 

Finally, make sure they wash their hands when they’re done playing and cleaning up.  Remind them that raw eggs can have a bacteria called Salmonella living in them and on them. 

Have fun!