friction

288

These are ripple marks in beach sand, made by the wind. Similar ripples can be seen in deserts, and even in large playground sandboxes. What causes the ripples to be so evenly spaced?

325

I took this photo at the beach. Looking at the tire tracks made me think about why car tires have treads, instead of being smooth, like racing tires. Why?

944

Ball on paper plate
If I roll the ball around the paper plate in the direction of the blue arrow, when it gets to the place where I cut out part of the plate, which path will it take? A, B or C? Why?

957

coiled snow structure
I photographed this snow structure on the drive home from the Utah Science Teachers Association conference. It is about six inches across, and there were many more of different sizes. How did it form?

961

lighter
When I was growing up, lighters made a spark by rubbing a metal wheel across a flint (which was not really made out of flint.) Lighters like this one ignite the flame in a different way. How is the gas ignited?

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