What are good mechanics experiments for 10 year olds? I'm trying to explain elementary mechanics - without the benefits of calculus or even algebra - and struggling. I'd like to find reasonable ways to demonstrate Newton's laws, minimally, and possibly continuing though basic projectile motion, although that may be too much to hope for.
 A: When you're driving, make them notice that if you're going at a constant speed, no matter how fast, they don't "feel" it. Yet, when accelerating from 0-40 they'll be pushed in their seats.
A: I remember enjoying the Webelos Scientist Activity Badge (part of the Boy Scouts program applicable to 10-year-olds).  (Here's a list of ideas.)  Don't need to get too fancy, and a lot of these make nice little projects, i.e. 'build a hot-air balloon' is a great problem-solving exercise (think about what shapes you can cut out from tissue-paper and glue together to make a sphere; hold over a toaster to fill it with hot air).  
Water rockets, model airplanes/gliders (even paper), potato cannon are also fun activities.
"How do airplanes fly" is a good question to think about, and refuting popular but incorrect ideas is a great critical thinking exercise.
At this age, it's probably more important to make science fun than to be totally pedantic.
There are lots of good conceptual points to ponder that could provide great topics for discussion:
How do tides work?  Why are there high tides simultaneously on opposite sides of the earth? (Hint: the earth doesn't "shield" gravity!)
How do rockets stay in orbit? 
Why does a mirror reverse left and right but not up and down?
What does it take to balance a see-saw?
Make a Mobius strip.
A: I am always fond of the experiment of "shooting" a rubber ball and dropping the same ball, and seeing that both of them will hit the ground at the same time, showing that the vertical and horizontal components of velocity are independent.
A: Galileo's Leaning Tower of Pisa experiment because it is sufficiently counter intuitive. 
A: Just some quick ideas.. the question is fairly intriguing: i'm gonna think about it again.
First law of Newton: i think that those dry ice containers that mimics the motion without friction can be found quite cheaply and can be very useful:


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*If set in motion it will keep going

*If connected to a dynamometer from one side and an eletric mini4WD in the other side can demonstrate (with no math at all.. just common sense) that an object stay still not only if no forces are acting upon it but also if the sum of the force actin on an object is zero  
Second Law: using the same electic mini 4WD as before, measure witha  dynamometer the force of the of the motor (u already did that in the previous experiment ;) ) and then vary the mass of the car. It will be quite evident (always thank to the common sense) that the heaviest car will accelerate less than the other..
Third law: take two object of similar but not equal mass and compress a spring between them: when you will release (yeah at the same time would be better:P ) them both of them will move in opposite direction.. that can be quite trickier to explain but the experimental evidence shuold be quite visible!
A: Measuring the acceleration of gravity with a pendulum seems to be a good candidate. You don't have to explain the maths. It's the first physics experiment I did, but I was older. On the other hand, it could work with a good teacher.
A: Tell a story.   Start say with the Aristotelian notion of why an arrow flies, you recall, wind circulating from the tip to the tail or something.   Then try to come up with experiments as to why that might be false, e.g. slow movements, movements in space, etc.
Look at crystals.  Grow some.   Weird, isn't it?   How could that be?    Atomic theory.
A: I whole heartedly suggest Lego. It's just amazing how many things about physics can be learnt from playing with the Lego Technic and Mindstorms series. When you're a child the most amazing thing in the world is making things and just watch them work. It's like magic, you know. So, you sit there furiously trying things, playing games in your mind and you start noticing things. You notice, while making a robotic arm, the farther away something heavy is from a joint the harder it is for the machine to lift stuff. Why?
What's happening over there? Then you realize that how heavy something is depends on how far it is from you on a rod. Weird. So, then you play some more and figure out how to use this to your advantage. After a while, you start learning tings, noticing things and start using them in your creations. It's just something natural and before you know it. You're in love.
I still love physics to this day thanks to that one Lego set. It really is magic.
A: Pythagorus's discovery on the length of strings, tension weights, sounds made.   Not too dynamic, however.
