Objects can easily slide past each other when the force of friction between them is low. Which of the following examples has the least amount of friction?

1. A soldier marching in sand

2. A skater practicing on ice

3. A truck driving on a road

4. A dog walking in the grass and pulling on his leash

1. A soldier marching on sand, I would say that this has some amount of friction being that when you step in sand you tend to sink, and that sliding would produce at least some friction.

2. A skater on ice. I would say that this would have the least amount of friction being that you slide easily on ice.

3. A truck driving on a road. Again, there would be some friction between the tires and the road being that tires are made to increase the friction with the ground so that they do not slide as much if they were going over a wet road.

3. A dog waling on grass and pulling a leash. This one is odd, but could still see some form of friction here being that the leash is pulled over the ground.

So ... I think 2 is your best bet here.